compiler: add debug info to synthetic wrapper functions

compiler/compiler.go

@@ -1264,6 +1264,11 @@ func (b *builder) createFunctionStart(intrinsic bool) {
 		} else if b.fn.Syntax() != nil {
 			// Create debug info file if needed.
 			b.difunc = b.attachDebugInfo(b.fn)
+		} else if b.fn.Pos().IsValid() {
+			// Synthetic wrappers such as $bound and $thunk have no syntax but share the
+			// position of the wrapped method. See https://pkg.go.dev/golang.org/x/tools/go/ssa#Function
+			pos := b.program.Fset.Position(b.fn.Pos())
+			b.difunc = b.attachDebugInfoRaw(b.fn, b.llvmFn, "", pos.Filename, pos.Line)
 		}
 		b.setDebugLocation(b.fn.Pos())
 	}

compiler/compiler_test.go

@@ -339,6 +339,44 @@ func TestAggregateExportedInterfaceABI(t *testing.T) {
 	}
 }
 
+func TestWrapperDebugInfo(t *testing.T) {
+	mod, errs := testCompilePackageWithDebug(t, &compileopts.Options{Target: "wasm"}, "wrapper-debug.go", true)
+	defer mod.Dispose()
+	for _, err := range errs {
+		t.Error(err)
+	}
+
+	for _, name := range []string{
+		"(main.wrapperValue).get$bound",
+		"(main.wrapperValue).get$thunk",
+		"(*main.wrapperValue).get",
+	} {
+		fn := mod.NamedFunction(name)
+		if fn.IsNil() {
+			t.Errorf("missing function %s", name)
+			continue
+		}
+		sp := fn.Subprogram()
+		if sp.IsNil() {
+			t.Errorf("%s has no subprogram", name)
+			continue
+		}
+		if line := sp.SubprogramLine(); line != 5 {
+			t.Errorf("%s subprogram line is %d, want 5", name, line)
+		}
+		if file := sp.ScopeFile().FileFilename(); !strings.HasSuffix(file, "wrapper-debug.go") {
+			t.Errorf("%s subprogram file is %q", name, file)
+		}
+		for bb := fn.FirstBasicBlock(); !bb.IsNil(); bb = llvm.NextBasicBlock(bb) {
+			for inst := bb.FirstInstruction(); !inst.IsNil(); inst = llvm.NextInstruction(inst) {
+				if !inst.IsACallInst().IsNil() && inst.InstructionDebugLoc().IsNil() {
+					t.Errorf("%s has a call without a debug location", name)
+				}
+			}
+		}
+	}
+}
+
 func TestValidateWasmFunctionParameters(t *testing.T) {
 	for _, test := range []struct {
 		name         string

compiler/testdata/wrapper-debug.go

@@ -0,0 +1,20 @@
+package main
+
+type wrapperValue struct{ n int }
+
+func (v wrapperValue) get() int {
+	return v.n
+}
+
+func boundWrapper(v wrapperValue) func() int {
+	return v.get
+}
+
+func thunkWrapper() func(wrapperValue) int {
+	return wrapperValue.get
+}
+
+func pointerWrapper(v *wrapperValue) int {
+	var i interface{ get() int } = v
+	return i.get()
+}