Fix thin archive member reproducer paths

Use the parent archive path hash and thin archive member name to form the generated input identity. This prevents members with identical basenames from colliding in --reproduce archives without depending on child offsets.

Resolves #1737

Author: rachitmeht

lib/Support/OutputTarWriter.cpp

@@ -74,10 +74,16 @@ void OutputTarWriter::addInputFile(const InputFile *File, bool IsLTOObject) {
 }
 
 std::string OutputTarWriter::getHashAndExtension(const Input *Ipt) const {
+  uint64_t InputHash = Ipt->getResolvedPathHash();
+  if (const auto *ArchiveMember = llvm::dyn_cast<ArchiveMemberInput>(Ipt))
+    // Thin archive members share the parent archive's resolved path. Include
+    // the member identity so members with the same basename cannot collide.
+    InputHash = llvm::hash_combine(InputHash, ArchiveMember->getMemberName());
+
   // Returns filename passed to the linker along with the file hash.
   return std::string(
              llvm::sys::path::filename(Ipt->getInputFile()->getMappedPath())) +
-         "." + std::to_string(Ipt->getResolvedPathHash());
+         "." + std::to_string(InputHash);
 }
 
 /// Create mapping.ini file of input filepath to its sha2 hash + file extension

test/Common/standalone/CommandLine/Reproduce/Inputs/a/foo.c

@@ -0,0 +1 @@
+int only_a(void) { return 1; }

test/Common/standalone/CommandLine/Reproduce/Inputs/b/foo.c

@@ -0,0 +1 @@
+int only_b(void) { return 2; }

test/Common/standalone/CommandLine/Reproduce/Inputs/thin-main.c

@@ -0,0 +1,4 @@
+extern int only_a(void);
+extern int only_b(void);
+
+int main(void) { return only_a() + only_b(); }

test/Common/standalone/CommandLine/Reproduce/ReproduceThinArchiveSameBasename.test

@@ -0,0 +1,27 @@
+#---ReproduceThinArchiveSameBasename.test----------------- Executable -----------------#
+
+#BEGIN_COMMENT
+# Checks that --reproduce preserves thin-archive members with the same basename.
+#END_COMMENT
+#START_TEST
+RUN: %rm -rf %t.tmpdir
+RUN: %mkdir %t.tmpdir
+RUN: %mkdir %t.tmpdir/a
+RUN: %mkdir %t.tmpdir/b
+RUN: %clang %clangopts -c %p/Inputs/a/foo.c -o %t.tmpdir/a/foo.o
+RUN: %clang %clangopts -c %p/Inputs/b/foo.c -o %t.tmpdir/b/foo.o
+RUN: %clang %clangopts -c %p/Inputs/thin-main.c -o %t.tmpdir/main.o
+RUN: cd %t.tmpdir
+RUN: %ar cr %aropts --thin %t.tmpdir/libsame.a a/foo.o b/foo.o
+RUN: %link --no-threads %t.tmpdir/main.o %t.tmpdir/libsame.a -o %t.same.out \
+RUN:   --reproduce %t.repro.tar --dump-mapping-file %t.mapping.ini
+RUN: %filecheck %s < %t.mapping.ini
+RUN: %mkdir %t.replay
+RUN: %tar %gnutaropts -xf %t.repro.tar -C %t.replay --strip-components=1
+RUN: cd %t.replay
+RUN: %python -c "import shlex, subprocess; args = shlex.split(open('response.txt').read())[1:]; args[args.index('-o') + 1] = r'%t.same.replay.out'; subprocess.check_call(shlex.split(r'%link') + args)"
+RUN: %diff %t.same.out %t.same.replay.out
+#END_TEST
+
+CHECK-DAG: Object/foo.o.{{[0-9]+}}
+CHECK-DAG: Object/foo.o.{{[0-9]+}}