Safe way to move from zlib to zlib-ng with compat?

[ScottESanDiego]

Installing `sys-libs/zlib-ng` with the `compat` USE flag of course is blocked by the already installed `sys-libs/zlib`. Unmerging `zlib` feels like a really bad idea, but I'm stuck as to how I'd migrate over to using `zlib-ng`.

What am I missing? How can I move a running system to `zlib-ng`?

[sam_]

Indeed, you should never have to unmerge anything. Always use depclean and if it refuses, it's for a good reason.

It should be enough to do a world upgrade with: emerge -a -uvDU @world sys-libs/zlib-ng. If that doesn't work, can you show the output in full please? virtual/zlib accepts either sys-libs/zlib or sys-libs/zlib-ng, so it should allow swapping with that hint from Portage that you want zlib-ng.

[ScottESanDiego]

Yeah, that's what I thought too. Unfortunately:

Code: Select all

intrepid ~ # emerge -a -uvDU @world sys-libs/zlib-ng

These are the packages that would be merged, in order:

Calculating dependencies... done!
Dependency resolution took 4.88 s (backtrack: 0/20).

[ebuild  N     ] sys-libs/zlib-ng-2.3.2::gentoo  USE="compat -static-libs -test" CPU_FLAGS_X86="avx2 avx512_vnni avx512f pclmul sse2 sse4_1 sse4_2 ssse3 vpclmulqdq" 2,390 KiB
[blocks B      ] sys-libs/zlib-ng[compat] ("sys-libs/zlib-ng[compat]" is soft blocking sys-libs/zlib-1.3.1-r1)
[blocks B      ] sys-libs/zlib ("sys-libs/zlib" is soft blocking sys-libs/zlib-ng-2.3.2)

Total: 1 package (1 new), Size of downloads: 2,390 KiB
Conflict: 2 blocks (2 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-libs/zlib-ng-2.3.2:0/0::gentoo, ebuild scheduled for merge) pulled in by
    sys-libs/zlib-ng

  (sys-libs/zlib-1.3.1-r1:0/1::gentoo, installed) pulled in by
    >=sys-libs/zlib-1.2.3:0/1= required by (net-misc/openssh-10.2_p1:0/0::gentoo, installed) USE="pam ssl -audit (-debug) -kerberos -ldns -libedit -livecd -security-key (-selinux) -static -test -verify-sig"
    >=sys-libs/zlib-1.3.1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?,static-libs?] (>=sys-libs/zlib-1.3.1[abi_x86_64(-)]) required by (virtual/zlib-1.3.1-r1:0/1::gentoo, installed) USE="-static-libs"
    >=sys-libs/zlib-1.2.8-r1:0/1=[abi_x86_64(-)] required by (dev-libs/libxml2-2.15.1:2/16::gentoo, installed) USE="readline -doc -icu -python -static-libs -test" PYTHON_TARGETS="python3_13 -python3_11 -python3_12 -python3_14"


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages

and

Code: Select all

intrepid ~ # emerge --depclean

 * Always study the list of packages to be cleaned for any obvious
 * mistakes. Packages that are part of the world set will always
 * be kept.  They can be manually added to this set with
 * `emerge --noreplace <atom>`.  Packages that are listed in
 * package.provided (see portage(5)) will be removed by
 * depclean, even if they are part of the world set.
 *
 * As a safety measure, depclean will not remove any packages
 * unless *all* required dependencies have been resolved.  As a
 * consequence of this, it often becomes necessary to run
 * `emerge --update --newuse --deep @world` prior to depclean.

Calculating dependencies... done!
>>> No packages selected for removal by depclean
>>> To see reverse dependencies, use --verbose
Packages installed:   656
Packages in world:    99
Packages in system:   50
Required packages:    656
Number removed:       0
intrepid ~ #
intrepid ~ # emerge --ask virtual/zlib

These are the packages that would be merged, in order:

Calculating dependencies... done!
Dependency resolution took 0.36 s (backtrack: 0/20).

[ebuild   R    ] virtual/zlib-1.3.1-r1

Would you like to merge these packages? [Yes/No] no

Quitting.

intrepid ~ #

[Hu]

Currently, that version of net-misc/openssh should be compatible. However, if you installed it before net-*/*: update for virtual/zlib, then yours might not be. Does emerge --oneshot net-misc/openssh remove it from the output? A similar situation applies to dev-libs/libxml2.

[sam_]

Similarly, does emerge --changed-deps -a -uvDU @world sys-libs/zlib-ng work?

[CaptainBlood]

sys-libs/zlib-ng as a sys-libs/zlib replacement seems reasonable from a performance perspective.

However things doesn't seem straight forward here:

Code: Select all

emerge -p -a -uvDU @world sys-libs/zlib-ng --exclude zig
Dependency resolution took 68.68 s (backtrack: 0/20).

[ebuild   R    ] sys-libs/zlib-ng-2.3.2::gentoo  USE="compat* -static-libs -test" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="avx2 -avx512_vnni -avx512f pclmul sse2 sse4_1 sse4_2 ssse3 -vpclmulqdq" 0 KiB
[blocks B      ] sys-libs/zlib-ng[compat] ("sys-libs/zlib-ng[compat]" is soft blocking sys-libs/zlib-1.3.1-r1)
[blocks B      ] sys-libs/zlib ("sys-libs/zlib" is soft blocking sys-libs/zlib-ng-2.3.2)

Total: 1 package (1 reinstall), Size of downloads: 0 KiB
Conflict: 2 blocks (2 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-libs/zlib-1.3.1-r1:0/1::gentoo, installed) pulled in by
    >=sys-libs/zlib-1.2.8-r1:0/1=[abi_x86_64(-)] required by (dev-libs/libxml2-compat-2.13.9:2/2::gentoo, installed) USE="-icu -lzma -readline -test" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (media-gfx/pngcrush-1.8.13:0/0::gentoo, installed) USE="" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (media-libs/libharu-2.4.5:0/2.4::gentoo, installed) USE="" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (media-libs/leptonica-1.85.0:0/6::gentoo, installed) USE="-gif jpeg -jpeg2k -png -static-libs -test tiff -utils -webp zlib" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (sci-libs/hdf5-1.14.6-r2:0/310-cmake::gentoo, installed) USE="cxx -debug fortran hl mpi -szip -test threads unsupported zlib" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (net-misc/aria2-1.37.0:0/0::gentoo, installed) USE="-adns -bittorrent (-gnutls) -jemalloc -libuv -libxml2 metalink -nettle -nls -scripts -sqlite -ssh ssl -tcmalloc -test xmlrpc" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.81.0-r101:1.81.0/1.81.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (sys-devel/mold-9999:0/0::local, installed) USE="-debug -test" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-19.1.7:19/19.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) doc -exegesis -libedit -libffi -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) SPIRV (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-15.0.7-r7:15/15::gentoo, installed) USE="binutils-plugin -debug -doc -exegesis -libedit -libffi -ncurses -test verify-sig -xar -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) (-ARC) (ARM) (AVR) (BPF) (-CSKY) (-DirectX) (Hexagon) (Lanai) (-LoongArch) (-M68k) (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) (-SPIRV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore)"
    sys-libs/zlib:0/1= required by (media-gfx/potrace-1.16-r1:0/0::gentoo, installed) USE="-metric" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (gui-apps/wlogout-1.2.2-r1-1:0/0::guru, installed) USE="" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-libs/libmirage-3.2.10:0/11::gentoo, installed) USE="-doc -introspection" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.82.0-r103:1.82.0/1.82.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (app-accessibility/julius-4.6:0/0::local, installed) USE="alsa -oss -portaudio -pulseaudio sndfile" ABI_X86="(64)" L10N="-ja"
    sys-libs/zlib:0/1= required by (gnome-extra/evolution-data-server-3.56.2-r1:0/64-11-21-4-3-27-2-27-4-0::gentoo, installed) USE="-berkdb -gnome-online-accounts -gtk -gtk-doc -introspection -kerberos -ldap -oauth-gtk3 -oauth-gtk4 -sound -test -vala -weather" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.90.0-r1:1.90.0/1.90.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa" RUST_SYSROOTS="-bpf wasm"
    sys-libs/zlib:0/1= required by (media-libs/openjpeg-2.5.3-r1:2/7::gentoo, installed) USE="-doc -test" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib[static-libs(+)] required by (media-gfx/splashutils-1.5.4.4-r101:0/0::local, installed) USE="fbcondecor -gpm -hardened -klibc png (-split-usr) -truetype" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.89.0:1.89.0/1.89.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    >=sys-libs/zlib-1.3.1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?,minizip] (>=sys-libs/zlib-1.3.1[abi_x86_64(-),minizip]) required by (virtual/minizip-1.3.1:0/1::gentoo, installed) USE="-static-libs" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (games-fps/xonotic-0.8.6-1:0/0::gentoo, installed) USE="X alsa ode -sdl" ABI_X86="(64)"
    sys-libs/zlib:= required by (app-text/stardict-4.0.0_pre20170304-r2:0/0::mv, installed) USE="-advertisement -cal -canberra -debug -dictdotcn -espeak -examples -flite -fortune -gnome -gucharmap -htmlparse -info -man -perl -powerwordparse -pronounce -qqwry -spell -tools -updateinfo -wikiparse -wordnet -xdxfparse -youdaodict" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (dev-db/sqlite-3.50.4:3/3::gentoo, installed) USE="-debug -doc -icu -readline secure-delete -static-libs -tcl -test -tools" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (dev-libs/boost-1.88.0-r1:0/1.88.0::gentoo, installed) USE="-bzip2 context -debug -doc icu -lzma mpi nls -numpy python stacktrace -test -test-full -tools zlib -zstd" ABI_X86="-32 (64) (-x32)" PYTHON_TARGETS="-python3_11 python3_12 -python3_13"
    sys-libs/zlib:0/1= required by (net-misc/dhcp-4.4.3_p1-r6:0/0::gentoo, installed) USE="-client -ipv6 -ldap (-selinux) server -ssl -vim-syntax" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.84.1-r2:1.84.1/1.84.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.83.0-r3:1.83.0/1.83.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (app-text/stardict-4.0.0_pre20170304-r2:0/0::mv, installed) USE="-advertisement -cal -canberra -debug -dictdotcn -espeak -examples -flite -fortune -gnome -gucharmap -htmlparse -info -man -perl -powerwordparse -pronounce -qqwry -spell -tools -updateinfo -wikiparse -wordnet -xdxfparse -youdaodict" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-20.1.8:20/20.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) -doc -exegesis -libedit -libffi -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) (SPIRV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1= required by (media-gfx/openvdb-11.0.0-r1:0/11.0::gentoo, installed) USE="-abi10-compat abi11-compat -abi12-compat -abi9-compat -alembic ax blosc (-cuda) -doc -examples -jpeg -nanovdb -numpy -openexr -png -python -static-libs -test -utils zlib" ABI_X86="(64)" CPU_FLAGS_X86="avx sse4_2" LLVM_SLOT="15" PYTHON_SINGLE_TARGET="-python3_11 -python3_12"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.79.0-r101:1.79.0/1.79.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.86.0-r2:1.86.0/1.86.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (dev-python/pillow-11.3.0:0/0::gentoo, installed) USE="-avif -debug -examples -imagequant jpeg jpeg2k lcms -test tiff -tk truetype webp -xcb zlib" ABI_X86="(64)" PYTHON_TARGETS="(-pypy3_11) -python3_11 python3_12 -python3_13 -python3_14"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.91.0:1.91.0/1.91.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(21)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa" RUST_SYSROOTS="-bpf wasm"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.80.1-r101:1.80.1/1.80.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (sys-devel/bpf-toolchain-15.2.0_p1:0/0::gentoo, installed) USE="bin-symlinks custom-cflags strip" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (llvm-core/lld-18.1.8-1:18/18.1::gentoo, installed) USE="-debug -test verify-sig zstd" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.85.1-r1:1.85.1/1.85.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (sys-apps/vbetool-1.2.2:0/0::gentoo, installed) USE="(-selinux)" ABI_X86="(64)"
    >=sys-libs/zlib-1.3.1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?,static-libs?] (>=sys-libs/zlib-1.3.1[abi_x86_64(-),static-libs]) required by (virtual/zlib-1.3.1-r1:0/1::gentoo, installed) USE="static-libs" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-18.1.8-r6:18/18.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) -doc -exegesis -libedit -libffi -ncurses -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) -SPIRV (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1= required by (llvm-core/lld-19.1.7-1:19/19.1::gentoo, installed) USE="-debug -test verify-sig zstd" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.88.0:1.88.0/1.88.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (app-text/podofo-0.10.3-r1:0/2::gentoo, installed) USE="-fontconfig -idn -jpeg -png -test -tiff -tools" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (sci-mathematics/glpk-5.0-r3:0/40::gentoo, installed) USE="-doc -examples gmp -mysql -odbc" ABI_X86="(64)"
    >=sys-libs/zlib-1.1.3:0/1= required by (dev-lang/python-2.7.18_p16-r2:2.7/2.7::gentoo, installed) USE="(-berkdb) -bluetooth -build -examples -gdbm -ncurses -readline -sqlite -ssl -tk -valgrind verify-sig -wininst -xml" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.87.0-r1:1.87.0/1.87.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (media-gfx/ipe-7.2.26:0/0::mv, installed) USE="" ABI_X86="(64)" LUA_SINGLE_TARGET="-lua5-3 lua5-4"
    sys-libs/zlib:0/1= required by (net-p2p/transmission-4.0.6-r6:0/0::gentoo, installed) USE="-appindicator -cli -debug gtk -mbedtls -nls -qt6 -systemd -test" ABI_X86="(64)"
    >=sys-libs/zlib-1.2.13:0/1=[abi_x86_64(-)] required by (dev-db/mysql-connector-c-8.0.36-1:0/21::gentoo, installed) USE="-ldap -static-libs" ABI_X86="-32 (64) (-x32)"

  (sys-libs/zlib-ng-2.3.2:0/0::gentoo, ebuild scheduled for merge) pulled in by
    sys-libs/zlib-ng
    sys-libs/zlib-ng[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (sys-libs/zlib-ng[abi_x86_64(-)]) required by (sys-libs/minizip-ng-4.0.10-r1:0/4::gentoo, installed) USE="-compat -lzma -openssl -test -zstd" ABI_X86="-32 (64) (-x32)"

Thks 4 ur attention, interest & support.

[sam_]

I refer you to my above question if you're also having issues.

[CaptainBlood]

Code: Select all

emerge -c -p

Packages installed:   3592
Packages in world:    882
Packages in system:   50
Required packages:    3592
Number to remove:     0

As sam lately suggests,

Code: Select all

emerge --changed-deps -p -a -uvDU @world sys-libs/zlib-ng --exclude zig

works fine with a huge rebuild cost.

Code: Select all

emerge --changed-deps -p -a -uvDU @world sys-libs/zlib-ng --exclude zig 2>/dev/null|grep ebuild|wc -l
744

That is over a quarter of installed packages.

I can't show the detailed list, many long lasting builds.

dpaste rejects creation with

Code: Select all

Sorry!

    __all__
        Possible TOS violation (financial crime)

EDIT: dpaste fixed.

.... should take many days here.

Thks 4 ur attention, interest & support.

[sam_]

Thanks. zlib is indeed a popular dependency (which is why we didn't revbump every single package depending on it).

[CaptainBlood]

Code: Select all

equery d virtual/zlib|grep -E "$.*"
app-admin/sudo-1.9.17_p2
app-admin/testdisk-7.2
app-arch/gcab-1.6
app-arch/libarchive-3.8.3
app-arch/libdeflate-1.24
app-arch/zstd-1.5.7-r1
app-crypt/gnupg-2.5.16
app-editors/emacs-30.2-r1
app-editors/emacs-31.0.9999
app-emulation/qemu-10.0.5
app-emulation/spice-0.16.0
app-forensics/aide-0.18.8
app-misc/broot-1.51.0
app-office/libreoffice-25.2.7.2-r1
app-office/texstudio-4.9.0
app-portage/portage-utils-0.97
app-text/dictd-1.13.3
app-text/dvipng-1.18
app-text/dvisvgm-3.4
app-text/evince-48.1
app-text/ghostscript-gpl-10.06.0
app-text/libabw-0.1.3-r1
app-text/libebook-0.1.3-r4
app-text/libetonyek-0.1.13
app-text/libmspub-0.1.4
app-text/libmwaw-0.3.22
app-text/libstaroffice-0.0.7
app-text/mandoc-1.14.6-r1
app-text/mupdf-1.25.6
app-text/podofo-0.10.3-r1
app-text/poppler-25.12.0
app-text/qpdf-12.2.0
app-text/sdcv-0.5.5
app-text/teckit-2.5.12
app-text/texlive-core-2024-r1
app-text/ttf2pk2-2.0_p20240311
dev-build/cmake-4.1.4
dev-build/meson-1.9.1
dev-db/mariadb-11.8.3-r2
dev-db/mysql-connector-c-8.0.36
dev-db/postgresql-14.20
dev-db/postgresql-15.15
dev-db/postgresql-16.11
dev-db/postgresql-17.7
dev-db/postgresql-18.1
dev-db/sqlite-3.50.4
dev-debug/gdb-16.3
dev-games/openscenegraph-3.6.5-r118
dev-games/simgear-2024.1.1
dev-java/openjdk-11.0.29_p7
dev-java/openjdk-17.0.17_p10
dev-java/openjdk-21.0.9_p10
dev-java/openjdk-25.0.1_p8-r1
dev-java/openjdk-8.472_p08
dev-java/openjdk-bin-11.0.29_p7
dev-java/openjdk-bin-17.0.17_p10
dev-java/openjdk-bin-21.0.9_p10
dev-java/openjdk-bin-25.0.1_p8
dev-java/openjdk-bin-8.472_p08
dev-lang/c3c-0.7.5
dev-lang/perl-5.42.0-r1
dev-lang/php-8.3.29
dev-lang/python-2.7.18_p16-r2
dev-lang/python-3.11.14
dev-lang/python-3.12.12
dev-lang/python-3.13.9
dev-lang/python-3.14.0_p1
dev-lang/ruby-3.3.8
dev-lang/rust-1.79.0-r101
dev-lang/rust-1.80.1-r101
dev-lang/rust-1.81.0-r101
dev-lang/rust-1.82.0-r103
dev-lang/rust-1.83.0-r3
dev-lang/rust-1.84.1-r2
dev-lang/rust-1.85.1-r1
dev-lang/rust-1.86.0-r2
dev-lang/rust-1.87.0-r1
dev-lang/rust-1.88.0
dev-lang/rust-1.89.0
dev-lang/rust-1.90.0-r1
dev-lang/rust-1.91.0
dev-lang/rust-1.92.0_p1-r1
dev-lang/rust-9999
dev-lang/spidermonkey-115.24.0
dev-lang/spidermonkey-128.13.0
dev-lang/swig-4.2.1
dev-lang/tcl-8.6.16
dev-libs/boost-1.88.0-r1
dev-libs/c-blosc-1.21.6-r1
dev-libs/capnproto-1.0.2
dev-libs/elfutils-0.193-r1
dev-libs/glib-2.84.4
dev-libs/imath-3.1.12-r1
dev-libs/libgit2-1.9.2
dev-libs/libmirage-3.2.10
dev-libs/liborcus-0.19.2-r1
dev-libs/libpcre-8.45-r4
dev-libs/libpcre2-10.47
dev-libs/librevenge-0.0.5
dev-libs/libxml2-2.15.1
dev-libs/libxml2-compat-2.13.9
dev-libs/libzip-1.11.4-r2
dev-libs/nss-3.119
dev-libs/openssl-3.5.4
dev-libs/openssl-compat-1.1.1u
dev-libs/protobuf-31.1
dev-libs/zziplib-0.13.80
dev-lisp/clisp-2.49.92-r3
dev-ml/camlzip-1.13
dev-python/pillow-11.3.0
dev-qt/qtbase-6.10.1
dev-qt/qtcore-5.15.18
dev-qt/qtgui-5.15.18
dev-qt/qtnetwork-5.15.18
dev-qt/qtquick3d-6.10.1
dev-qt/qtsvg-5.15.18
dev-qt/qtsvg-6.10.1
dev-qt/qtwebengine-6.10.1
dev-ruby/nokogiri-1.18.10
dev-util/android-tools-35.0.2
dev-util/cargo-c-0.10.16
dev-util/intel-ocl-sdk-18.1.0.015-r1
dev-util/mesa_clc-25.2.7
dev-util/pahole-1.30
dev-util/pycharm-community-2025.1.3
dev-util/rizin-0.8.1
dev-util/trace-cmd-3.3.2
dev-vcs/git-2.52.0
games-action/supertuxkart-1.4-r1
games-fps/alienarena-7.66-r1
games-fps/xonotic-0.8.6
games-simulation/flightgear-2024.1.1
games-strategy/0ad-0.27.1
gnome-extra/evolution-data-server-3.56.2-r1
gui-apps/wlogout-1.2.2-r1
gui-libs/neatvnc-0.9.2
kde-apps/ark-25.08.3
kde-frameworks/karchive-6.20.0
kde-plasma/libksysguard-6.5.4
kde-plasma/plasma-workspace-6.5.4
llvm-core/lld-18.1.8
llvm-core/lld-19.1.7
llvm-core/lld-20.1.8
llvm-core/lld-21.1.8
llvm-core/llvm-15.0.7-r7
llvm-core/llvm-18.1.8-r6
llvm-core/llvm-19.1.7
llvm-core/llvm-20.1.8
llvm-core/llvm-21.1.8
lxqt-base/lxqt-config-2.3.0
media-gfx/alembic-1.8.8
media-gfx/blender-4.5.5
media-gfx/blender-5.0.0
media-gfx/exiv2-0.28.7
media-gfx/fbgrab-1.5
media-gfx/freecad-1.0.2-r2
media-gfx/gimp-3.0.6
media-gfx/graphicsmagick-1.3.46
media-gfx/graphviz-12.2.1-r1
media-gfx/imagemagick-7.1.2.5
media-gfx/netgen-6.2.2505
media-gfx/openvdb-11.0.0-r1
media-gfx/optipng-0.7.8
media-gfx/pngcheck-3.0.3
media-gfx/pngcrush-1.8.13
media-gfx/potrace-1.16-r1
media-gfx/povray-3.7.0.0-r6
media-gfx/scantailor-advanced-1.0.19
media-gfx/xsane-0.999-r6
media-libs/coin-4.0.6
media-libs/freetype-2.14.1-r1
media-libs/gd-2.3.3-r4
media-libs/gegl-0.4.64-r1
media-libs/gst-plugins-base-1.24.11-r1
media-libs/gst-plugins-good-1.24.11
media-libs/imlib2-1.12.5
media-libs/leptonica-1.85.0
media-libs/lib3mf-2.4.1-r1
media-libs/libcdr-0.1.8
media-libs/libfreehand-0.1.2-r2
media-libs/libharu-2.4.5
media-libs/libheif-1.20.2
media-libs/libid3tag-0.16.3
media-libs/libmng-2.0.3-r1
media-libs/libpng-1.6.51
media-libs/libspng-0.7.4
media-libs/libzmf-0.0.2-r1
media-libs/mesa-25.2.7
media-libs/netpbm-11.2.19
media-libs/opencollada-1.6.68-r2
media-libs/opencv-4.11.0-r1
media-libs/openimageio-3.0.11.0
media-libs/openjpeg-2.5.3-r1
media-libs/osl-1.14.7.0
media-libs/raptor-2.0.16-r1
media-libs/sdl-image-1.2.12_p20220527-r1
media-libs/sdl2-image-2.8.5-r1
media-libs/simage-1.8.3-r1
media-libs/taglib-2.1.1
media-libs/tiff-4.7.0-r1
media-sound/audacity-3.7.5-r1
media-sound/milkytracker-1.05.01
media-sound/mpd-0.24.5
media-sound/sox-14.4.2_p20210509-r3
media-sound/spotify-1.2.77
media-sound/yoshimi-2.3.4.1
media-tv/kodi-21.3
media-video/ffmpeg-7.1.3
media-video/ffmpeg-compat-6.1.3
media-video/mkvtoolnix-95.0
media-video/mplayer-1.5_p20241125-r2
media-video/mpv-0.41.0
media-video/smplayer-25.6.0_p20250903-r1
net-analyzer/net-snmp-5.9.4-r3
net-analyzer/nmap-7.95
net-analyzer/wireshark-4.6.0-r1
net-dns/bind-9.18.42
net-fs/samba-4.22.5-r1
net-libs/gloox-1.0.24-r1
net-libs/gnutls-3.8.11
net-libs/libsoup-3.6.5-r1
net-libs/libssh-0.11.3
net-libs/libssh2-1.11.1
net-libs/libtorrent-0.15.7
net-libs/libwebsockets-4.4.1-r1
net-libs/neon-0.34.0
net-libs/nghttp2-1.65.0-r2
net-libs/nodejs-22.13.1
net-libs/webkit-gtk-2.48.5-r411
net-misc/aria2-1.37.0
net-misc/curl-8.17.0-r1
net-misc/dhcp-4.4.3_p1-r6
net-misc/freerdp-3.14.1
net-misc/gerbera-2.5.0
net-misc/mosh-1.4.0-r1
net-misc/openssh-10.2_p1
net-misc/rsync-3.4.1-r1
net-misc/wget-1.25.0-r1
net-news/newsboat-2.41
net-p2p/transmission-4.0.6-r6
net-print/cups-2.4.14-r1
net-print/libppd-2.1.1
net-proxy/privoxy-3.0.34-r1
net-vpn/tor-0.4.8.21
sci-libs/cfitsio-4.6.3
sci-libs/coinor-utils-2.11.9
sci-libs/gmsh-4.14.1
sci-libs/hdf5-1.14.6-r2
sci-libs/netcdf-4.9.3-r2
sci-libs/vtk-9.4.2-r2
sci-mathematics/cgal-6.0.1
sci-mathematics/gap-4.14.0-r1
sci-mathematics/glpk-5.0-r3
sci-mathematics/nauty-2.8.8-r1
sci-mathematics/rstudio-desktop-bin-2024.12.0_p467-r1
sci-mathematics/sagemath-10.8
sys-apps/eza-0.23.3
sys-apps/file-5.46-r3
sys-apps/kbd-2.9.0-r1
sys-apps/kmod-34.2
sys-apps/man-db-2.13.1
sys-apps/pciutils-3.14.0
sys-apps/util-linux-2.41.2
sys-apps/vbetool-1.2.2
sys-cluster/openmpi-4.1.6-r1
sys-devel/binutils-2.45.1
sys-devel/bpf-toolchain-15.2.0_p1
sys-devel/gcc-12.5.0
sys-devel/gcc-13.4.1_p20251016
sys-devel/gcc-14.3.1_p20251017
sys-devel/gcc-15.2.1_p20251122
sys-fs/ext4magic-0.3.2-r2
sys-kernel/kpatch-0.9.8
sys-libs/binutils-libs-2.45.1
sys-libs/cracklib-2.10.3
sys-libs/libunwind-1.8.2-r1
sys-libs/slang-2.3.3-r1
sys-process/atop-2.12.1
www-apps/invidious-2025.09.13.0-r2
www-client/dillo-9999
www-client/lynx-2.9.2
www-client/w3m-0.5.3_p20240916
www-servers/apache-2.4.65
www-servers/gatling-0.16-r6
x11-apps/igt-gpu-tools-2.3
x11-apps/mkfontscale-1.2.3
x11-libs/cairo-1.18.4-r1
x11-libs/fltk-1.3.8
x11-libs/gl2ps-1.4.2-r1
x11-libs/libXfont2-2.0.7
x11-libs/libfontenc-1.1.8
x11-libs/libpciaccess-0.18.1
x11-libs/wxGTK-3.2.8.1-r2
x11-terms/kitty-0.44.0

Albeit "equery -d" output should be taken with a pinch of salt, some packages shown here also are in the above dpaste.

Thks 4 ur attention, interest & support.

[sam_]

I suspect that goes off the current effective dependencies, not what the ebuild now says (see what I said above).

[Perfect Gentleman]

I just unmerged sys-libs/zlib and merged sys-libs/{zlib-ng,minizip-ng}[compat]. That's all.

[Zucca]

I just unmerged sys-libs/zlib

There's huge risk of having a broken system if you don't let Portage replace the zlib implementation.

The danger lies at the point after the unmerge, and before the new implementation is in the system.

[Perfect Gentleman]

I just unmerged sys-libs/zlib

There's huge risk of having a broken system if you don't let Portage replace the zlib implementation.
The danger lies at the point after the unmerge, and before the new implementation is in the system.

Did it on 3 systems, all of them work fine.

[Zucca]

Did it on 3 systems, all of them work fine.

The topic title is "Safe way to move from zlib to zlib-ng with compat?". Doing unmerge isn't safe in this context, no matter how you put it. It may work on your setups, but OP specifically asked for a safe way to do the switch.

Code: Select all

       --unmerge, -C
              WARNING:  This  action can remove important packages! Re‐
              moves all matching packages following a counter  governed
              by  CLEAN_DELAY.   This does no checking of dependencies,
              so it may remove packages necessary for the proper opera‐
              tion of your system.   Its  arguments  can  be  atoms  or
              ebuilds. For a dependency aware version of --unmerge, use
              --depclean or --prune.  For a version with CLEAN_DELAY=0,
              use --rage-clean.

[CaptainBlood]

Wouldn't binary packaging of sys-libs/zlib be safe enough prior to removal?
Or would there be a problem if it's restoration is required?

Thks 4 ur attention, interest & support.

[Zucca]

Wouldn't binary packaging of sys-libs/zlib be safe enough prior to removal?
Or would there be a problem if it's restoration is required?

Thks 4 ur attention, interest & support.

It might help to package zlib first, yes. Or let's say, "would greatly help" if your system were to break because of this. But at least you'd have to make sure, BINPKG_COMPRESS isn't set to something that needs zlib (gzip at least).

[CaptainBlood]

Good point,
Let's find it out.

Thks 4 ur attention, interest & support.

[CaptainBlood]

Code: Select all

tar -tf /var/cache/binpkgs/sys-libs/zlib/zlib-1.3.1-r1-1.gpkg.tar 
zlib-1.3.1-r1/gpkg-1
zlib-1.3.1-r1/metadata.tar.xz
zlib-1.3.1-r1/image.tar.xz
zlib-1.3.1-r1/Manifest

any advice how to temporary switch to gzip?

EDIT:
/etc/portage/make.conf snippet;

Code: Select all

#zstd default
BINPKG_COMPRESS="xz"
#old xpak default
BINPKG_FORMAT="gpkg"

seems to be the place temporary change as:

Code: Select all

#zstd default
BINPKG_COMPRESS="xz"
BINPKG_COMPRESS="bzip2"
#old xpak default
BINPKG_FORMAT="gpkg"

brings:

Code: Select all

tar -tf /var/cache/binpkgs/sys-libs/zlib/zlib-1.3.1-r1-2.gpkg.tar 
zlib-1.3.1-r1/gpkg-1
zlib-1.3.1-r1/metadata.tar.bz2
zlib-1.3.1-r1/image.tar.bz2
zlib-1.3.1-r1/Manifest

Thks 4 ur attention, interest & support.

[CaptainBlood]

As a result here is now:

Code: Select all

emerge -p -uvDU @world --exclude zig

 * IMPORTANT: 2 config files in '/etc/portage' need updating.
 * See the CONFIGURATION FILES and CONFIGURATION FILES UPDATE TOOLS
 * sections of the emerge man page to learn how to update config files.

These are the packages that would be merged, in reverse order:

Calculating dependencies  !!!
... done!
Dependency resolution took 125.61 s (backtrack: 0/20).

[nomerge       ] x11-wm/xpra-6.2.5-r1::gentoo  USE="X -avif -brotli client -clipboard -crypt -csc (-cuda) -cups -dbus -debug (-doc) -examples -gstreamer -gtk3 -html -ibus -jpeg -lz4 -mdns minimal -oauth -opengl -openh264 -pinentry -pulseaudio -qrcode server -sound -systemd -test -trayicon -udev -vpx -webcam -webp -x264 -xdg -xinerama" PYTHON_SINGLE_TARGET="-python3_11 python3_12 -python3_13" VIDEO_CARDS="-nvidia" 
[nomerge       ]  x11-misc/shared-mime-info-2.4-r3::gentoo  USE="-test" 
[nomerge       ]   dev-libs/libxml2-2.15.1:2/16::gentoo  USE="-doc icu python -readline -static-libs -test" ABI_X86="-32 (64) (-x32)" PYTHON_TARGETS="-python3_11 python3_12 -python3_13 -python3_14" 
[nomerge       ]    app-text/doxygen-1.13.2::gentoo  USE="-clang -debug -doc dot -doxysearch -gui -test" LLVM_SLOT="-18 19 -20" 
[nomerge       ]     dev-db/sqlite-3.50.4:3::gentoo  USE="-debug -doc -icu -readline secure-delete -static-libs -tcl -test -tools" ABI_X86="-32 (64) (-x32)" 
[ebuild  N     ]      sys-libs/zlib-1.3.1-r1:0/1::gentoo  USE="minizip static-libs verify-sig" ABI_X86="-32 (64) (-x32)" 0 KiB
[blocks B      ] sys-libs/zlib-ng[compat] ("sys-libs/zlib-ng[compat]" is soft blocking sys-libs/zlib-1.3.1-r1)
[blocks B      ] sys-libs/zlib ("sys-libs/zlib" is soft blocking sys-libs/zlib-ng-2.3.2)

Total: 1 package (1 new), Size of downloads: 0 KiB
Conflict: 2 blocks (2 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-libs/zlib-1.3.1-r1:0/1::gentoo, ebuild scheduled for merge) pulled in by
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (dev-libs/boost-1.88.0-r1:0/1.88.0::gentoo, installed) USE="-bzip2 context -debug -doc icu -lzma mpi nls -numpy python stacktrace -test -test-full -tools zlib -zstd" ABI_X86="-32 (64) (-x32)" PYTHON_TARGETS="-python3_11 python3_12 -python3_13"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.87.0-r1:1.87.0/1.87.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (media-gfx/pngcrush-1.8.13:0/0::gentoo, installed) USE="" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (app-text/stardict-4.0.0_pre20170304-r2:0/0::mv, installed) USE="-advertisement -cal -canberra -debug -dictdotcn -espeak -examples -flite -fortune -gnome -gucharmap -htmlparse -info -man -perl -powerwordparse -pronounce -qqwry -spell -tools -updateinfo -wikiparse -wordnet -xdxfparse -youdaodict" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-18.1.8-r6:18/18.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) -doc -exegesis -libedit -libffi -ncurses -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) -SPIRV (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1= required by (media-libs/libharu-2.4.5:0/2.4::gentoo, installed) USE="" ABI_X86="(64)"
    >=sys-libs/zlib-1.1.3:0/1= required by (dev-lang/python-2.7.18_p16-r2:2.7/2.7::gentoo, installed) USE="(-berkdb) -bluetooth -build -examples -gdbm -ncurses -readline -sqlite -ssl -tk -valgrind verify-sig -wininst -xml" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (net-misc/aria2-1.37.0:0/0::gentoo, installed) USE="-adns -bittorrent (-gnutls) -jemalloc -libuv -libxml2 metalink -nettle -nls -scripts -sqlite -ssh ssl -tcmalloc -test xmlrpc" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.84.1-r2:1.84.1/1.84.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (sys-devel/mold-9999:0/0::local, installed) USE="-debug -test" ABI_X86="(64)"
    >=sys-libs/zlib-1.3.1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?,minizip] (>=sys-libs/zlib-1.3.1[abi_x86_64(-),minizip]) required by (virtual/minizip-1.3.1:0/1::gentoo, installed) USE="-static-libs" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (media-gfx/potrace-1.16-r1:0/0::gentoo, installed) USE="-metric" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-20.1.8:20/20.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) -doc -exegesis -libedit -libffi -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) (SPIRV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.80.1-r101:1.80.1/1.80.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib[static-libs(+)] required by (media-gfx/splashutils-1.5.4.4-r101:0/0::local, installed) USE="fbcondecor -gpm -hardened -klibc png (-split-usr) -truetype" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.85.1-r1:1.85.1/1.85.1::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (media-gfx/ipe-7.2.26:0/0::mv, installed) USE="" ABI_X86="(64)" LUA_SINGLE_TARGET="-lua5-3 lua5-4"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.83.0-r3:1.83.0/1.83.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib required by (app-accessibility/julius-4.6:0/0::local, installed) USE="alsa -oss -portaudio -pulseaudio sndfile" ABI_X86="(64)" L10N="-ja"
    sys-libs/zlib:0/1= required by (sci-libs/hdf5-1.14.6-r2:0/310-cmake::gentoo, installed) USE="cxx -debug fortran hl mpi -szip -test threads unsupported zlib" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-python/pillow-11.3.0:0/0::gentoo, installed) USE="-avif -debug -examples -imagequant jpeg jpeg2k lcms -test tiff -tk truetype webp -xcb zlib" ABI_X86="(64)" PYTHON_TARGETS="(-pypy3_11) -python3_11 python3_12 -python3_13 -python3_14"
    sys-libs/zlib:0/1= required by (media-gfx/openvdb-11.0.0-r1:0/11.0::gentoo, installed) USE="-abi10-compat abi11-compat -abi12-compat -abi9-compat -alembic ax blosc (-cuda) -doc -examples -jpeg -nanovdb -numpy -openexr -png -python -static-libs -test -utils zlib" ABI_X86="(64)" CPU_FLAGS_X86="avx sse4_2" LLVM_SLOT="15" PYTHON_SINGLE_TARGET="-python3_11 -python3_12"
    sys-libs/zlib:0/1= required by (llvm-core/lld-19.1.7-1:19/19.1::gentoo, installed) USE="-debug -test verify-sig zstd" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (sys-devel/bpf-toolchain-15.2.0_p1:0/0::gentoo, installed) USE="bin-symlinks custom-cflags strip" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (app-text/podofo-0.10.3-r1:0/2::gentoo, installed) USE="-fontconfig -idn -jpeg -png -test -tiff -tools" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-libs/libmirage-3.2.10:0/11::gentoo, installed) USE="-doc -introspection" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (gnome-extra/evolution-data-server-3.56.2-r1:0/64-11-21-4-3-27-2-27-4-0::gentoo, installed) USE="-berkdb -gnome-online-accounts -gtk -gtk-doc -introspection -kerberos -ldap -oauth-gtk3 -oauth-gtk4 -sound -test -vala -weather" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.91.0:1.91.0/1.91.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(21)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa" RUST_SYSROOTS="-bpf wasm"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.86.0-r2:1.86.0/1.86.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (media-libs/leptonica-1.85.0:0/6::gentoo, installed) USE="-gif jpeg -jpeg2k -png -static-libs -test tiff -utils -webp zlib" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (gui-apps/wlogout-1.2.2-r1-1:0/0::guru, installed) USE="" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (sys-apps/vbetool-1.2.2:0/0::gentoo, installed) USE="(-selinux)" ABI_X86="(64)"
    sys-libs/zlib:= required by (app-text/stardict-4.0.0_pre20170304-r2:0/0::mv, installed) USE="-advertisement -cal -canberra -debug -dictdotcn -espeak -examples -flite -fortune -gnome -gucharmap -htmlparse -info -man -perl -powerwordparse -pronounce -qqwry -spell -tools -updateinfo -wikiparse -wordnet -xdxfparse -youdaodict" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.89.0:1.89.0/1.89.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (dev-db/sqlite-3.50.4:3/3::gentoo, installed) USE="-debug -doc -icu -readline secure-delete -static-libs -tcl -test -tools" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (games-fps/xonotic-0.8.6-1:0/0::gentoo, installed) USE="X alsa ode -sdl" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (llvm-core/lld-18.1.8-1:18/18.1::gentoo, installed) USE="-debug -test verify-sig zstd" ABI_X86="(64)"
    sys-libs/zlib:0/1= required by (net-p2p/transmission-4.0.6-r6:0/0::gentoo, installed) USE="-appindicator -cli -debug gtk -mbedtls -nls -qt6 -systemd -test" ABI_X86="(64)"
    >=sys-libs/zlib-1.2.13:0/1=[abi_x86_64(-)] required by (dev-db/mysql-connector-c-8.0.36-1:0/21::gentoo, installed) USE="-ldap -static-libs" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-15.0.7-r7:15/15::gentoo, installed) USE="binutils-plugin -debug -doc -exegesis -libedit -libffi -ncurses -test verify-sig -xar -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) (-ARC) (ARM) (AVR) (BPF) (-CSKY) (-DirectX) (Hexagon) (Lanai) (-LoongArch) (-M68k) (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) (-SPIRV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.90.0-r1:1.90.0/1.90.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa" RUST_SYSROOTS="-bpf wasm"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.88.0:1.88.0/1.88.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(20)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (sci-mathematics/glpk-5.0-r3:0/40::gentoo, installed) USE="-doc -examples gmp -mysql -odbc" ABI_X86="(64)"
    sys-libs/zlib:0/1=[abi_x86_64(-)] required by (llvm-core/llvm-19.1.7:19/19.1::gentoo, installed) USE="binutils-plugin -debug (-debuginfod) doc -exegesis -libedit -libffi -test verify-sig -xml z3 zstd" ABI_X86="-32 (64) (-x32)" LLVM_TARGETS="(AArch64) (AMDGPU) -ARC (ARM) (AVR) (BPF) -CSKY -DirectX (Hexagon) (Lanai) (LoongArch) -M68k (MSP430) (Mips) (NVPTX) (PowerPC) (RISCV) SPIRV (Sparc) (SystemZ) (VE) (WebAssembly) (X86) (XCore) -Xtensa"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.81.0-r101:1.81.0/1.81.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.82.0-r103:1.82.0/1.82.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(19)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (net-misc/dhcp-4.4.3_p1-r6:0/0::gentoo, installed) USE="-client -ipv6 -ldap (-selinux) server -ssl -vim-syntax" ABI_X86="(64)"
    >=sys-libs/zlib-1.3.1[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?,static-libs?] (>=sys-libs/zlib-1.3.1[abi_x86_64(-),static-libs]) required by (virtual/zlib-1.3.1-r1:0/1::gentoo, installed) USE="static-libs" ABI_X86="-32 (64) (-x32)"
    >=sys-libs/zlib-1.2.8-r1:0/1=[abi_x86_64(-)] required by (dev-libs/libxml2-compat-2.13.9:2/2::gentoo, installed) USE="-icu -lzma -readline -test" ABI_X86="-32 (64) (-x32)"
    sys-libs/zlib:0/1= required by (dev-lang/rust-1.79.0-r101:1.79.0/1.79.0::gentoo, installed) USE="(-big-endian) clippy -debug -dist doc (-llvm-libunwind) -lto miri nightly -parallel-compiler rust-analyzer rust-src rustfmt -system-llvm -test verify-sig wasm" ABI_X86="-32 (64) (-x32)" CPU_FLAGS_X86="sse2" LLVM_SLOT="(18)" LLVM_TARGETS="-AArch64 -AMDGPU -ARC -ARM -AVR -BPF -CSKY -DirectX -Hexagon -Lanai -LoongArch -M68k -MSP430 -Mips -NVPTX -PowerPC -RISCV -SPIRV -Sparc -SystemZ -VE WebAssembly (X86) -XCore -Xtensa"
    sys-libs/zlib:0/1= required by (media-libs/openjpeg-2.5.3-r1:2/7::gentoo, installed) USE="-doc -test" ABI_X86="-32 (64) (-x32)"

  (sys-libs/zlib-ng-2.3.2:0/0::gentoo, installed) pulled in by
    sys-libs/zlib-ng[abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?,abi_s390_32(-)?,abi_s390_64(-)?] (sys-libs/zlib-ng[abi_x86_64(-)]) required by (sys-libs/minizip-ng-4.0.10-r1:0/4::gentoo, installed) USE="-compat -lzma -openssl -test -zstd" ABI_X86="-32 (64) (-x32)"

For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages

Not sure to be ready to fix manually...
Time to fallback to virtual/zlib... and think it over.

Thks 4 ur attention, interest & support.

[Perfect Gentleman]

Did it on 3 systems, all of them work fine.

The topic title is "Safe way to move from zlib to zlib-ng with compat?". Doing unmerge isn't safe in this context, no matter how you put it. It may work on your setups, but OP specifically asked for a safe way to do the switch.

Code: Select all

       --unmerge, -C
              WARNING:  This  action can remove important packages! Re‐
              moves all matching packages following a counter  governed
              by  CLEAN_DELAY.   This does no checking of dependencies,
              so it may remove packages necessary for the proper opera‐
              tion of your system.   Its  arguments  can  be  atoms  or
              ebuilds. For a dependency aware version of --unmerge, use
              --depclean or --prune.  For a version with CLEAN_DELAY=0,
              use --rage-clean.

I know that majority here doesn't look for easy ways, that's okay. Finding the longest and hardest way is the way of samurai here.

[CaptainBlood]

Perfect Gentleman doesn't seems to have any of those problematic packages installed...
Lucky chap

Thks 4 ur attention, interest & support.

[Hu]

I know that majority here doesn't look for easy ways, that's okay. Finding the longest and hardest way is the way of samurai here.

This is not about trying to find the hardest method of achieving the goal. This is about ensuring that users do not unknowingly put their systems into a state where an ill-timed interruption leaves the system both degraded and unable to readily repair itself. The interruption could be as simple as a blackout that forcibly powers down the system. I've seen posters here mention having suffered that failure. We also have plenty of laptop users, some of whom have mentioned in passing having the laptop's battery run out while in use. The interruption could also be social in nature: the user gets a phone call, walks away from the system, and doesn't finish the migration on returning. We strongly push users not to pursue paths that are unnecessarily high risk. If you want to chance that your system will be fine, go ahead, but do not encourage others to take such risks. Your first post stated having done the unmerge, with no mention of the risks associated with an interruption. When Zucca challenged you on it, you reiterated that your results were fine, which may be true, but does not negate Zucca's point that some systems risk a failure that would require expert intervention to repair.

[ScottESanDiego]

Currently, that version of net-misc/openssh should be compatible. However, if you installed it before net-*/*: update for virtual/zlib, then yours might not be. Does emerge --oneshot net-misc/openssh remove it from the output? A similar situation applies to dev-libs/libxml2.

Indeed, that was it. Thanks Hu. Re-emerging openssh and libxml lets the update to zlib-ng proceed as I'd expected it to originally.

Code: Select all

intrepid ~ # emerge --ask sys-libs/zlib-ng

These are the packages that would be merged, in order:

Calculating dependencies... done!
Dependency resolution took 1.00 s (backtrack: 0/20).

[ebuild  N     ] sys-libs/zlib-ng-2.3.2  USE="compat -static-libs -test" CPU_FLAGS_X86="avx2 avx512_vnni avx512f pclmul sse2 sse4_1 sse4_2 ssse3 vpclmulqdq"
[uninstall     ] sys-libs/zlib-1.3.1-r1
[blocks b      ] sys-libs/zlib ("sys-libs/zlib" is soft blocking sys-libs/zlib-ng-2.3.2)
[blocks b      ] sys-libs/zlib-ng[compat] ("sys-libs/zlib-ng[compat]" is soft blocking sys-libs/zlib-1.3.1-r1)

Would you like to merge these packages? [Yes/No]

[ScottESanDiego]

Similarly, does emerge --changed-deps -a -uvDU @world sys-libs/zlib-ng work?

No, that didn't work.