warning: overriding the module target triple with x86_64-apple-macosx10.15.0

[yhara]

After #280, I got the following warning.

$ cargo run -- run examples/a.sk
   Compiling shiika v0.0.1 (/Users/yhara/Dropbox/proj/shiika)
    Finished dev [unoptimized + debuginfo] target(s) in 12.80s
     Running `/Users/yhara/tmp/shiika/debug/shiika run examples/a.sk`
[src/code_gen/mod.rs:59] &inkwell::targets::TargetMachine::get_default_triple() = TargetTriple("x86_64-apple-darwin19.6.0")
clang-9: warning: argument unused during compilation: '-no-pie' [-Wunused-command-line-argument]
warning: overriding the module target triple with x86_64-apple-macosx10.15.0 [-Woverride-module]
1 warning generated.
warning: overriding the module target triple with x86_64-apple-macosx10.15.0 [-Woverride-module]
1 warning generated.

The program itself works fine, but these warnings are a bit annoying.

[yhara]

Why clang tries to "override" the target triple to macosx10.15.0 while get_default_triple returns darwin19.6.0?

$ clang --version
clang version 9.0.1
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /usr/local/opt/llvm@9/bin

[yhara]

The warning is generated here:

• https://github.com/llvm/llvm-project/blob/d480f968ad8b56d3ee4a6b6df5532d485b0ad01e/clang/lib/CodeGen/CodeGenAction.cpp#L1064

[yhara]

My guess is:

• llvm@9 installed by homebrew is configured as "darwin" (= any of macOS, iOS, etc.)
• clang detects it is running on "macosx"
• the warning is shown

I found crystal-lang fixes this problem here. This is true until crystal runs on iOS or watchOS.

[yhara]

Hmm, replace is not enough because .replace("darwin", "macosx") results in "x86_64-apple-macosx19.4.0", not "x86_64-apple-macosx10.15.0" (the version is wrong.)

[yhara]

Thanks to @LEA0317, we've found that clang computes "effective" target triple. That's why other commands like llvm-config --host-target or dsymutil --version just shows darwin and only clang shows macosx.

rustc reads special envvar for this issue.
rust-lang/rust#60235 (comment)

So there should be two ways to suppress this warning.

1. Create a string "x86_64-apple-macosx19.4.0" somehow and use it for .bc's target triple.
2. Explicitly specify target triple by clang's -target option.

But 1. is practically impossible because the clang's algorithm is pretty long and depends on heuristics. PR #282 fixes this issue by solution 2.

[yhara]

Found one more case this warning appears.

[src/targets.rs:4] &inkwell::targets::TargetMachine::get_default_triple() = TargetTriple("x86_64-apple-darwin21.4.0")
[src/targets.rs:13] &s = "x86_64-apple-macosx12.3"
warning: overriding the module target triple with x86_64-apple-macosx12.3.0 [-Woverride-module]

mac-sys-info crate returns macosx12.3 but clang expects macosx12.3.0