It's needed by some crates, like cc or it's revdeps.
cc crate's options documented here https://crates.io/crates/cc External configuration via environment variables To control the programs and flags used for building, the builder can set a number of different environment variables. CFLAGS - a series of space separated flags passed to compilers. Note that individual flags cannot currently contain spaces, so doing something like: "-L=foo\ bar" is not possible. CC - the actual C compiler used. Note that this is used as an exact executable name, so (for example) no extra flags can be passed inside this variable, and the builder must ensure that there aren't any trailing spaces. This compiler must understand the -c flag. For certain TARGETs, it also is assumed to know about other flags (most common is -fPIC). AR - the ar (archiver) executable to use to build the static library. CRATE_CC_NO_DEFAULTS - the default compiler flags may cause conflicts in some cross compiling scenarios. Setting this variable will disable the generation of default compiler flags. Each of these variables can also be supplied with certain prefixes and suffixes, in the following prioritized order: <var>_<target> - for example, CC_x86_64-unknown-linux-gnu <var>_<target_with_underscores> - for example, CC_x86_64_unknown_linux_gnu <build-kind>_<var> - for example, HOST_CC or TARGET_CFLAGS <var> - a plain CC, AR as above. If none of these variables exist, cc-rs uses built-in defaults In addition to the above optional environment variables, cc-rs has some functions with hard requirements on some variables supplied by cargo's build-script driver that it has the TARGET, OUT_DIR, OPT_LEVEL, and HOST variables.
another one is PKG_CONFIG, I've seen unprefixed calls to in -sys crates.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=6d3f2059166f6d8c460c7e60523a3e224438348d commit 6d3f2059166f6d8c460c7e60523a3e224438348d Author: Georgy Yakovlev <gyakovlev@gentoo.org> AuthorDate: 2020-06-02 08:44:40 +0000 Commit: Georgy Yakovlev <gyakovlev@gentoo.org> CommitDate: 2020-06-02 08:54:56 +0000 cargo.eclass: tc-export AR CC Bug: https://bugs.gentoo.org/726428 Closes: https://bugs.gentoo.org/726714 Signed-off-by: Georgy Yakovlev <gyakovlev@gentoo.org> eclass/cargo.eclass | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) Additionally, it has been referenced in the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=8fd7ffef828ccbdf83fff0eb4aac58ae7f5d1bc5 commit 8fd7ffef828ccbdf83fff0eb4aac58ae7f5d1bc5 Author: Georgy Yakovlev <gyakovlev@gentoo.org> AuthorDate: 2020-06-02 08:53:05 +0000 Commit: Georgy Yakovlev <gyakovlev@gentoo.org> CommitDate: 2020-06-02 08:54:57 +0000 x11-terms/alacritty: remove CC export how set in eclass Bug: https://bugs.gentoo.org/726428 Bug: https://bugs.gentoo.org/726714 This reverts commit 941788b2803ed563bdc1984c7966df1b86bda4fa. Signed-off-by: Georgy Yakovlev <gyakovlev@gentoo.org> x11-terms/alacritty/alacritty-0.4.2-r1.ebuild | 3 +-- x11-terms/alacritty/alacritty-0.4.3.ebuild | 3 +-- x11-terms/alacritty/alacritty-9999.ebuild | 3 +-- 3 files changed, 3 insertions(+), 6 deletions(-)
