new [gcc] build failure and other questions

[jacktose]

Now that Homebrew/linuxbrew-core#21380 is in (🎊!), I tried to reinstall gcc, but it's failing to build. Here's approximately what I did:

1. Start with linuxbrew with nonstandard prefix (many things have to build), and old gcc & gcc@5.
2. brew upgrade gcc Fails with compiler error.
3. Thinking existing gcc/gcc@5 are interfering, brew unlink those and retry brew upgrade gcc. Fails with same compiler error.
4. Thinking unlinking isn't enough, brew remove those (and isl@0.18 to finally resolve brew dr warning) and brew install gcc. Fails with different compiler error! Progress!
5. Okay, really clean house! brew remove a bunch of related formulae and other leaves and retry brew install gcc. Successfully (re)installs some dependencies, but gcc fails with differenter compiler error! Progress?

So question 1: How can I get gcc to install?

Question 2: Wait, what's with those dependencies from step 5??
==> Installing dependencies for gcc: isl@0.18, libmpc, glibc and gcc@5
isl@0.18, glibc, & gcc@5 aren't supposed to be required:

ad-user-ads-11 ~ ★ brew info gcc
...
==> Dependencies
Required: gmp ✔, isl ✔, libmpc ✔, mpfr ✔, zlib ✔, binutils ✔
...

ad-user-ads-11 ~ ★ brew deps --include-build gcc
binutils
gmp
isl
libmpc
m4
mpfr
zlib

Maybe I just don't understand something about brew's dependency model? I tried to investigate, but I don't see why step 5 did what it did. The full log of my flailing is here.
Edit: Dependency thing doesn't seem specific to gcc. brew upgrade gh also tried to install those three:
==> Installing dependencies for gh: isl@0.18, glibc and gcc@5

Edit: question 3: For the good of the order, does this represent any kind of problem with the gcc setup from Homebrew/linuxbrew-core#21380, that other users might experience when upgrading or installing?

[iMichka]

What is your system compiler? Can you give us a copy of brew config?

[jacktose]

ad-user-ads-11 ~ ★ lsb_release -a
LSB Version:    :core-4.1-amd64:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-4.1-amd64:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1-noarch
Distributor ID: CentOS
Description:    CentOS Linux release 7.9.2009 (Core)
Release:        7.9.2009
Codename:       Core

ad-user-ads-11 ~ ★ which -a gcc
/bin/gcc
/usr/bin/gcc
ad-user-ads-11 ~ ★ /bin/gcc --version
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ad-user-ads-11 ~ ★ /usr/bin/gcc --version
gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

ad-user-ads-11 ~ ★ brew config
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
HOMEBREW_VERSION: 3.0.4-42-g2d1d20a
ORIGIN: https://github.com/Homebrew/brew
HEAD: 2d1d20a236c8f5d868605e54e4c0365bd5d50ebb
Last commit: 8 hours ago
Core tap ORIGIN: https://github.com/Homebrew/linuxbrew-core
Core tap HEAD: a14551589b28153e97141e0a877b145567b10e09
Core tap last commit: 3 hours ago
Core tap branch: master
HOMEBREW_PREFIX: /data/shared/lusers/jacktose/.linuxbrew
HOMEBREW_REPOSITORY: /data/shared/lusers/jacktose/.linuxbrew/Homebrew
HOMEBREW_CELLAR: /data/shared/lusers/jacktose/.linuxbrew/Cellar
HOMEBREW_CASK_OPTS: []
HOMEBREW_EDITOR: vim
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_MAKE_JOBS: 2
Homebrew Ruby: 2.6.3 => /data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/bin/ruby
CPU: dual-core 64-bit ivybridge
Clang: N/A
Git: 2.20.1 => /usr/local/bin/git
Curl: 7.61.1 => /usr/lusers/jacktose/bin/curl
Kernel: Linux 3.10.0-862.6.3.el7.x86_64 x86_64 GNU/Linux
OS: CentOS Linux release 7.9.2009 (Core) (Core)
Host glibc: 2.17
/usr/bin/gcc: 4.8.5
/usr/bin/ruby: N/A
glibc: 2.23
gcc@5: 5.5.0_6
xorg: N/A

Also added brew config & brew doctor to gist.

[danielnachun]

In my experience our GCC formulae don't build with brewed glibc because during the bootstrap process one of the early compiler binaries ends up linking to the system glibc but uses the ld linker from brewed glibc. Since gcc is relocatable, the solution I've been using has just been to install gcc with brew install --force-bottle gcc.

For now I think we could manually add cellar: any to the gcc formulae, until we figure out how to make sure our relocation testing ignores the cellar references in the gcc binaries.

[iMichka]

Yes, can you try brew install --force-bottle gcc please?

we could manually add cellar: any to the gcc formulae

No, I have been doing this over the past 3 years and always forget to add it back. This needs to be fixed in brew's bottling code, once and for all.

[jacktose]

It's a relocatable bottle? Then why the heck am I building it?
The gcc bottle seems to work, but it's still installing those extra dependencies. Also note “Please report this issue” near the bottom.

ad-user-ads-11 ~ ★ brew install --force-bottle gcc
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
==> Downloading https://linuxbrew.bintray.com/bottles/isl%400.18-0.18.x86_64_linux.bottle.tar.gz
Already downloaded: /usr/lusers/jacktose/.cache/Homebrew/downloads/1e71394174ea74a433f7b62c1ceb3b96dd2a496dd19a98cf57cfac4522a7cf94--isl@0.18-0.18.x86_64_linux.bottle.tar.gz
Warning: Building glibc from source as the bottle needs:
- HOMEBREW_CELLAR: /home/linuxbrew/.linuxbrew/Cellar (yours is /data/shared/lusers/jacktose/.linuxbrew/Cellar)
- HOMEBREW_PREFIX: /home/linuxbrew/.linuxbrew (yours is /data/shared/lusers/jacktose/.linuxbrew)
==> Downloading https://ftp.gnu.org/gnu/glibc/glibc-2.23.tar.gz
Already downloaded: /usr/lusers/jacktose/.cache/Homebrew/downloads/3c17421daad583cfd4fad587b8e1260f19385344f309d7ae11e0c2bb6b75d801--glibc-2.23.tar.gz
==> Downloading https://linuxbrew.bintray.com/bottles/gcc%405-5.5.0_6.x86_64_linux.bottle.tar.gz
Already downloaded: /usr/lusers/jacktose/.cache/Homebrew/downloads/12b5fbb8ba21e5dc08dbc80a033b329239518f4313549117645c7126b5440a40--gcc@5-5.5.0_6.x86_64_linux.bottle.tar.gz
==> Downloading https://linuxbrew.bintray.com/bottles/gcc-10.2.0_4.x86_64_linux.bottle.tar.gz
==> Downloading from https://akamai.bintray.com/e6/e62efea399fd03d854ff871210b941e5c3277d821e9148badceeda883f53f016?__gda__=exp=1615020095~hmac=1788863c3ed582a6b28174fb87c7cfde28a4fb15793d1c7a6c098b7f75a4fbee&response
######################################################################## 100.0%
==> Installing dependencies for gcc: isl@0.18, glibc and gcc@5
Warning: isl@0.18 has been deprecated because it is a versioned formula!
==> Installing gcc dependency: isl@0.18
==> Pouring isl@0.18-0.18.x86_64_linux.bottle.tar.gz
==> Caveats
isl@0.18 is keg-only, which means it was not symlinked into /data/shared/lusers/jacktose/.linuxbrew,
because this is an alternate version of another formula.

For compilers to find isl@0.18 you may need to set:
  export LDFLAGS="-L/data/shared/lusers/jacktose/.linuxbrew/opt/isl@0.18/lib"
  export CPPFLAGS="-I/data/shared/lusers/jacktose/.linuxbrew/opt/isl@0.18/include"

For pkg-config to find isl@0.18 you may need to set:
  export PKG_CONFIG_PATH="/data/shared/lusers/jacktose/.linuxbrew/opt/isl@0.18/lib/pkgconfig"

==> Summary
🍺  /data/shared/lusers/jacktose/.linuxbrew/Cellar/isl@0.18/0.18: 81 files, 6.4MB
==> Installing gcc dependency: glibc
==> ../configure --disable-debug --disable-dependency-tracking --disable-silent-rules --prefix=/data/shared/lusers/jacktose/.linuxbrew/Cellar/glibc/2.23 --enable-obsolete-rpc --without-selinux --with-binutils=/data/sh
==> make
==> make install
==> Installing locale data for en_US.UTF-8
==> /data/shared/lusers/jacktose/.linuxbrew/Cellar/glibc/2.23/bin/localedef -i en_US -f UTF-8 en_US.UTF-8
🍺  /data/shared/lusers/jacktose/.linuxbrew/Cellar/glibc/2.23: 1,405 files, 41.4MB, built in 14 minutes 1 second
==> Installing gcc dependency: gcc@5
==> Pouring gcc@5-5.5.0_6.x86_64_linux.bottle.tar.gz
==> Creating the GCC specs file: /data/shared/lusers/jacktose/.linuxbrew/Cellar/gcc@5/5.5.0_6/bin/../lib/gcc/5/gcc/x86_64-unknown-linux-gnu/5.5.0/specs
🍺  /data/shared/lusers/jacktose/.linuxbrew/Cellar/gcc@5/5.5.0_6: 1,347 files, 172.9MB
==> Installing gcc
==> Pouring gcc-10.2.0_4.x86_64_linux.bottle.tar.gz
==> Creating the GCC specs file: /data/shared/lusers/jacktose/.linuxbrew/Cellar/gcc/10.2.0_4/bin/../lib/gcc/10/gcc/x86_64-pc-linux-gnu/10.2.0/specs
🍺  /data/shared/lusers/jacktose/.linuxbrew/Cellar/gcc/10.2.0_4: 1,489 files, 264.1MB
==> No outdated dependents to upgrade!
==> Checking for dependents of upgraded formulae...
==> Reinstalling 3 broken dependents from source:
berkeley-db, binutils, mpdecimal
==> Downloading https://linuxbrew.bintray.com/bottles/berkeley-db-18.1.40.x86_64_linux.bottle.tar.gz
Already downloaded: /usr/lusers/jacktose/.cache/Homebrew/downloads/ad4ec0b1d3720119ce5e2cb3b49f073969f0ca9fbd76f7b34e5e62947a721bb3--berkeley-db-18.1.40.x86_64_linux.bottle.tar.gz
==> Reinstalling berkeley-db 
==> Pouring berkeley-db-18.1.40.x86_64_linux.bottle.tar.gz
🍺  /data/shared/lusers/jacktose/.linuxbrew/Cellar/berkeley-db/18.1.40: 44 files, 8MB
Error: undefined method `fetch' for nil:NilClass
Please report this issue:
  https://docs.brew.sh/Troubleshooting
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/formula_installer.rb:1124:in `fetch'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/reinstall.rb:50:in `reinstall_formula'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/upgrade.rb:239:in `block in check_installed_dependents'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/upgrade.rb:238:in `each'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/upgrade.rb:238:in `check_installed_dependents'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/cmd/install.rb:319:in `install'
/data/shared/lusers/jacktose/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:122:in `<main>'

ad-user-ads-11 ~ ★ brew info gcc
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
gcc: stable 10.2.0, HEAD
GNU compiler collection
https://gcc.gnu.org/
/data/shared/lusers/enneking/.linuxbrew/Cellar/gcc/10.2.0_4 (1,489 files, 264.1MB) *
  Poured from bottle on 2021-03-06 at 00:44:07
From: https://github.com/Homebrew/linuxbrew-core/blob/HEAD/Formula/gcc.rb
License: GPL-3.0-or-later with GCC-exception-3.1
==> Dependencies
Required: gmp ✔, isl ✔, libmpc ✔, mpfr ✔, zlib ✔, binutils ✔
==> Options
--HEAD
        Install HEAD version
==> Analytics
install: 10,611 (30 days), 31,883 (90 days), 119,764 (365 days)
install-on-request: 8,066 (30 days), 22,363 (90 days), 85,598 (365 days)
build-error: 0 (30 days)

ad-user-ads-11 ~ ★ brew test gcc
Warning: HOMEBREW_NO_ENV_FILTERING is undocumented, deprecated and will be removed in a future Homebrew release (because it breaks many things)!
==> Testing gcc
==> /data/shared/lusers/enneking/.linuxbrew/Cellar/gcc/10.2.0_4/bin/gcc-10 -o hello-c hello-c.c
==> /data/shared/lusers/enneking/.linuxbrew/Cellar/gcc/10.2.0_4/bin/g++-10 -o hello-cc hello-cc.cc
==> /data/shared/lusers/enneking/.linuxbrew/Cellar/gcc/10.2.0_4/bin/gfortran -o test test.f90