Fix external library repeated build issue by avoiding in-place artifact modification

[Copilot]

Problem

When building a binary project with external shared libraries using maturin, the second build would fail with an error like:

💥 maturin failed
  Caused by: Cannot repair wheel, because required library libTypeTreeGeneratorAPI-849c9bc2.so could not be located.

This issue occurred because maturin was modifying the original binary artifacts in-place during the wheel repair process, causing subsequent builds to look for hashed library names instead of the original library files.

Root Cause

The issue was in the external library handling workflow in build_context.rs:

1. First build: Binary links to libTypeTreeGeneratorAPI.so, maturin copies it with a hash suffix (libTypeTreeGeneratorAPI-849c9bc2.so) and modifies the binary's DT_NEEDED entries to point to the hashed name
2. Second build: The already-modified binary is analyzed and reports dependencies on libTypeTreeGeneratorAPI-849c9bc2.so instead of the original libTypeTreeGeneratorAPI.so
3. Build fails: maturin tries to find the hashed library name on the filesystem but only the original exists

Solution

Restructured the external library handling workflow to avoid modifying original artifacts:

Key Changes

1. Pre-process artifacts: Created prepare_modified_artifacts() function that creates temporary copies of artifacts before any wheel writing begins
2. Use modified copies: Updated write_bin_wheel() to use these modified copies for both wheel content and patchelf operations
3. Preserve originals: Original artifacts in the Cargo target directory are never modified

Code Flow

// Before (problematic):
write_bin(&artifact.path)          // Add original to wheel
patchelf::replace_needed(&artifact.path)  // Modify original in-place ❌

// After (fixed):
let modified_path = create_copy_and_modify(&artifact.path)  // Create temp copy
write_bin(&modified_path)          // Add modified copy to wheel ✅
// Original artifact unchanged ✅

Testing

Verified the fix with the reproduction case from jakobhellermann/repro:

# Before fix: second build fails
RUSTFLAGS="-L libs" maturin build  # ✅ succeeds
RUSTFLAGS="-L libs" maturin build  # ❌ fails

# After fix: all builds succeed
RUSTFLAGS="-L libs" maturin build  # ✅ succeeds  
RUSTFLAGS="-L libs" maturin build  # ✅ succeeds
RUSTFLAGS="-L libs" maturin build  # ✅ succeeds

All existing unit tests pass, confirming no regressions.

Fixes

Closes #2680

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[messense]

@copilot could you please simplify it by copying the artifacts to target/maturin/auditwheel before in-place modification?

[Copilot]

@copilot could you please simplify it by copying the artifacts to target/maturin/auditwheel before in-place modification?

Done! I've simplified the implementation as suggested by copying artifacts to target/maturin/auditwheel before in-place modification. This removes the complex temporary directory and mapping logic, making the code much cleaner and easier to understand. Commit d74d74a implements this approach.