bootstrap: Fix file permissions when dereferencing symlinks

[smpdt]

Problem

When copying files in the bootstrap process with dereference_symlinks = true, we're incorrectly using the symlink's metadata to set permissions on the copied regular file, which results in the following error:

Warning: Failed to set file times for "/build/nix-build-rustc-1.86.0.drv-0/rustc-1.86.0-src/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/bin/llvm-strip" (permissions: Permissions(FilePermissions { mode: 0o100000 (----------) })) error: Permission denied (os error 13)

Verbose Logs confirming the error:

TRACE: Found llvm-strip copy operation
  Source: /n/nix/tech/store/n34yzv2n50p6lbjmx089vjym121wbl4j-llvm-19.1.7/bin/llvm-strip
  Destination: /build/nix-build-rustc-1.86.0.drv-0/rustc-1.86.0-src/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/bin/llvm-strip
  Source is_symlink (via symlink_metadata): true
  Source symlink_metadata permissions: 120000
  Source symlink_metadata file_type: FileType { is_file: false, is_dir: false, is_symlink: true, .. }

  Source is symlink pointing to: llvm-objcopy
  Source raw mode: 120000
  Source filetype: 120000

  Setting permissions: Permissions(FilePermissions { mode: 0o120000 (l---------) })
  Permission mode to set: 120000
  Raw permission bits: 120000
  File type bits being set: 120000
  Permission bits being set: 0

  WARNING: Attempting to set symlink file type (120000) on regular file!
  WARNING: Setting zero permission bits will make file inaccessible!
  Destination permissions after set_permissions: 100000 

Solution

After canonicalizing a symlink path, fetch the metadata of the target file instead of continuing to use the symlink's metadata. This ensures:

• Correct file type detection
• Proper permission bits for the target file
• Maintains existing behavior for non-symlink cases

Testing

Verified fix resolves permission errors:

rustc> llvm-strip: Original metadata mode: 120000, is_symlink: true
rustc> llvm-strip: Target metadata mode after fix: 100555
rustc> llvm-strip: Final permissions mode: 100555

[rustbot]

r? @Kobzol

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[Kobzol]

Makes sense, thanks!

@bors r+ rollup

[bors]

📌 Commit 9091a94 has been approved by Kobzol

It is now in the queue for this repository.