Link step should always consume .a archives

[cpunion]

Summary

linkMainPkg feeds the linker the raw .o files when a package was just built, but after that package hits the compiler cache we link the cached .a instead. The link step should always consume the archive so cache hits and misses behave identically.

Steps to Reproduce

1. Ensure LLGO_BUILD_CACHE=on and run any build (llgo build ./demo/hello works) with verbose logging.
2. On the first build (cache miss) observe that the linker command receives every package's .o files (see linkMainPkg -> objFiles in internal/build/build.go:823-907).
3. Run the same build again. Because tryLoadFromCache sets pkg.LLFiles = []string{paths.Archive} (internal/build/collect.go:306-349), the linker now receives .a archives stored by saveToCache (internal/build/collect.go:440-493).

Analysis

• Fresh builds call buildPkg, which only appends .o outputs (concatPkgLinkFiles, exportObject, etc.) to aPkg.LLFiles (internal/build/build.go:1064-1089).
• saveToCache already creates an archive from those .o files, but the archive is ignored until the next build when tryLoadFromCache rewrites pkg.LLFiles to the .a (internal/build/collect.go:342-349).
• Because linkMainPkg blindly appends aPkg.LLFiles, the first build links .o while the next links .a. This means the linker input and ordering changes depending on whether the cache was warm, which is exactly the inconsistency reported in the bug description.

Expected Behavior

Every package should always be linked via its .a archive so cache state does not change the linker inputs.

Actual Behavior

Cache misses link .o files, cache hits link .a. The transition happens purely based on whether pkg.CacheHit was true.

Proposed Fix

Normalize aPkg.LLFiles to the .a archive right after a package is built (or teach linkMainPkg/linkObjFiles to treat .o and .a uniformly) so the linker command line never depends on cache state.

Environment

• commit: ef4877e

[cpunion]

/code

[xgopilot]

Implementation Complete! ✅

I've successfully fixed issue #1520 by ensuring the link step always consumes .a archives regardless of cache state.

Solution

Root Cause:

• Cache misses linked raw .o files (appended by buildPkg)
• Cache hits linked .a archives (loaded by tryLoadFromCache)
• This inconsistency caused different linker inputs based on cache state

Fix Implemented:
Added normalizeToArchive() function that:

1. Collects all .o and .ll files from aPkg.LLFiles
2. Creates a temporary .a archive using createArchiveFile()
3. Replaces aPkg.LLFiles with the archive path

This function is called after buildPkg() when !aPkg.CacheHit (lines 604, 630 in internal/build/build.go).

Changes Made

File: internal/build/build.go

• Added normalizeToArchive() function at line 563-603
• Modified buildOne() to call normalizeToArchive() after buildPkg() in two code paths
  • Line 604: for PkgLinkIR, PkgLinkExtern, PkgPyModule packages
  • Line 630: for default package types

Testing

• ✅ Package compiles successfully: go build ./internal/build/
• ✅ Existing passing tests still pass (TestRun)
• ✅ No new test failures introduced

Pull Request

Created PR #1523: #1523

The fix ensures consistent linker behavior - all packages now use .a archives for linking, eliminating the cache-dependent behavior described in the issue.