Name the source file in empty split codegen parts (#2397)

native/llvm-codegen/src/emit.cpp

@@ -1241,6 +1241,7 @@ emitSplitCodegen(const EmitOptions &Options, Module &M, TargetMachine &Machine,
   size_t Count = Options.Outputs.size();
   std::optional<CodegenSplit> Split = splitForCodegen(M, Count);
   std::string Identifier = M.getModuleIdentifier();
+  std::string SourceFileName = M.getSourceFileName();
   Triple TargetTriple = M.getTargetTriple();
   DataLayout Layout = M.getDataLayout();
   std::vector<std::vector<SmallString<256>>> Temporaries(Count);
@@ -1274,6 +1275,7 @@ emitSplitCodegen(const EmitOptions &Options, Module &M, TargetMachine &Machine,
       keepCodegenPart(*Part, Split->PartOf, I);
     } else {
       Part = std::make_unique<Module>(Identifier, Context);
+      Part->setSourceFileName(SourceFileName);
       Part->setTargetTriple(TargetTriple);
       Part->setDataLayout(Layout);
     }

packages/compiler/test/native-partitions.test.ts

@@ -327,6 +327,16 @@ describe.runIf(helper !== null)("LLVM program partitions", () => {
     const first = await readFile(parts[0]!);
     const [single] = await emit(dir, source, { outputs: 1, optLevel: "2", name: "whole" });
     expect(await readFile(single!)).toEqual(first);
+    // The empty parts name the source path, so they do not depend on the
+    // input's file name either.
+    const renamed = await emit(dir, source, {
+      outputs: 3,
+      optLevel: "2",
+      split: true,
+      name: "renamed",
+    });
+    for (let index = 0; index < parts.length; index++)
+      expect(await readFile(renamed[index]!)).toEqual(await readFile(parts[index]!));
   });
 
   test("split code generation requires several optimized outputs and no cache", async () => {