[wrapper] Make cc_wrapper.sh POSIX-compliant and use #!/bin/sh

[RyanTorok]

Some Linux distributions, such as NixOS, do not provide /bin/bash. This PR aims to make the LLVM toolchain compatible with these platforms by only using POSIX-compatible features in the shell script and replacing the shebang with #!/bin/sh.

Prior to this change, attempting to use the LLVM toolchain to build a C/C++ target on NixOS causes an error like:

src/main/tools/linux-sandbox-pid1.cc:548: "execvp(external/toolchains_llvm~~llvm~llvm_toolchain/bin/cc_wrapper.sh, 0x1ce8a310)": No such file or directory

where the No such file or directory error is referring to /bin/bash, not the cc_wrapper.sh script itself. In fact, trying to run bazel-REPONAME/external/toolchains_llvm~~llvm~llvm_toolchain/bin/cc_wrapper.sh manually afterwards gives a Required file not found error.

This PR emerged out of a discussion on #543, where it was noticed that replacing the #!/bin/bash shebang with #!/usr/bin/env bash causes issues when the calling rule does not include /usr/bin in PATH (rules_rust hits this case).

This PR does not update the corresponding MacOS script, as all MacOS platforms should have /bin/bash.

Supercedes #543.

[Copilot]

Pull Request Overview

This PR makes the cc_wrapper.sh shell script POSIX-compliant to support Linux distributions like NixOS that don't provide /bin/bash. The change replaces bash-specific features with POSIX shell equivalents while maintaining the same functionality.

Key changes:

• Replace #!/bin/bash shebang with #!/bin/sh
• Convert bash arrays and associative constructs to POSIX-compatible alternatives
• Replace bash-specific syntax with POSIX shell equivalents

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[fmeum]

This is a case in which Copilot comments are highly relevant and much more thorough than what I could provide. Please take a look.

[RyanTorok]

This is a case in which Copilot comments are highly relevant and much more thorough than what I could provide. Please take a look.

Copilot was quick to remind me that POSIX shells don't support the same nice syntax for regular expressions as bash. After fixing the issues it pointed out, I was able to get several of the test scripts to pass in an Ubuntu container, so hopefully CI will pass this time :)

[RyanTorok]

Trying to rewrite cc_wrapper.sh.tpl to be POSIX-compliant caused too many bugs, and more importantly, required eliding a bunch of safety checks. The original script uses arrays and regular expressions everywhere, and replacing these with POSIX-compatible equivalents was very unidiomatic and unsafe.

As an alternative, I moved the current cc_wrapper.sh.tpl to cc_wrapper_inner.sh.tpl, and created a new cc_wrapper.sh.tpl that searches for an instance of bash on the host, either directly at /bin/bash or through /usr/bin/env/PATH. Once a valid instance of bash is found, it is used to call cc_wrapper_inner.sh.

[RyanTorok]

Can a maintainer please re-run CI on this PR?

[helly25]

Can a maintainer please re-run CI on this PR?

I checked the errors and it appears that the new inner script is still not present. So somewhere it is not being copied as it needs to.