Search codegen backends based on target libdir instead of sysroot

[o01eg]

Fixes #57014

Fixes cases with custom libdir when it consists of two or more parts.

[rust-highfive]

r? @davidtwco

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[davidtwco]

r? @alexcrichton

[alexcrichton]

@bors: r+

[bors]

📌 Commit 4e7d53d has been approved by alexcrichton

[bors]

⌛ Testing commit 4e7d53d with merge 6861426...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 6861426 to master...

[rust-highfive]

📣 Toolstate changed by #57101!

Tested on commit 6861426.
Direct link to PR: #57101

💔 miri on windows: test-pass → test-fail (cc @oli-obk @RalfJung @eddyb, @rust-lang/infra).

[RalfJung]

Uh... any idea why this would affect Miri only on Windows, and what we could do about that?

The error is

error: failed to find a `codegen-backends` folder in the libdir candidates:
* C:\projects\rust\build\x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\lib
* \\?\C:\projects\rust\build\x86_64-pc-windows-msvc\stage2\bin
* \\?\C:\projects\rust\build\x86_64-pc-windows-msvc\stage2\bin\rustlib\x86_64-pc-windows-msvc\lib

[o01eg]

It's strange. What is correct place of codegen library?

[RalfJung]

I have no idea, I hoped you'd tell me.^^

[o01eg]

I suppose it could be broken because windows places dynamic libraries in the "bin" folder.

[o01eg]

I'm afraid other tools will fail as well but they were already broken.

[mati865]

Unfortunately it broke all the tools for MSVC target: #57303

I suppose it could be broken because windows places dynamic libraries in the "bin" folder.

That's correct, for both Windows target bin must be in PATH.

[o01eg]

How are executable binaries and codegen and rustc_driver libraries placed on windows? It looks like it requires other way to calculate target libdir and codegen folder.

[matthiaskrgr]

I'm afraid other tools will fail as well but they were already broken.

They would have been fixed by #57303 but the pr broke them in a way I cannot fix as I don't have windows.

Could you please provide a fix for this?

[mati865]

Generally the only difference in files placement between UNIX and Windows (MinGW at least) should be runtime lib placement. On UNIX they are inside /usr/lib and on Windows they are usually located alongside executables because they have to be in PATH.

Here is the tree of MinGW toolchain installed with rustup: tree.txt

[o01eg]

I could try to fix it after tomorrow. I think it better to revert PR now and then I try to fix it.
But it better to make a test to prevent this breakage.