internal/refactor/inline: fix bug in shadow detection

There's a kink in the scope tree at Func{Decl,Lit}
that we forgot to straighten out in all cases.
Fixed, with test.

Change-Id: Iaed9636b4cc17537af6b607b153f8b4183ac7cb7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/531699
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: adonovan

internal/refactor/inline/callee.go

@@ -472,7 +472,7 @@ func analyzeParams(logf func(string, ...any), fset *token.FileSet, info *types.I
 // for the reference.
 func addShadows(shadows map[string]bool, info *types.Info, exclude string, stack []ast.Node) map[string]bool {
 	for _, n := range stack {
-		if scope, ok := info.Scopes[n]; ok {
+		if scope := scopeFor(info, n); scope != nil {
 			for _, name := range scope.Names() {
 				if name != exclude {
 					if shadows == nil {

internal/refactor/inline/inline.go

@@ -1536,12 +1536,7 @@ func createBindingDecl(logf func(string, ...any), caller *Caller, args []*argume
 func (caller *Caller) lookup(name string) types.Object {
 	pos := caller.Call.Pos()
 	for _, n := range caller.path {
-		// The function body scope (containing not just params)
-		// is associated with FuncDecl.Type, not FuncDecl.Body.
-		if decl, ok := n.(*ast.FuncDecl); ok {
-			n = decl.Type
-		}
-		if scope := caller.Info.Scopes[n]; scope != nil {
+		if scope := scopeFor(caller.Info, n); scope != nil {
 			if _, obj := scope.LookupParent(name, pos); obj != nil {
 				return obj
 			}
@@ -1550,6 +1545,18 @@ func (caller *Caller) lookup(name string) types.Object {
 	return nil
 }
 
+func scopeFor(info *types.Info, n ast.Node) *types.Scope {
+	// The function body scope (containing not just params)
+	// is associated with the function's type, not body.
+	switch fn := n.(type) {
+	case *ast.FuncDecl:
+		n = fn.Type
+	case *ast.FuncLit:
+		n = fn.Type
+	}
+	return info.Scopes[n]
+}
+
 // -- predicates over expressions --
 
 // freeVars returns the names of all free identifiers of e:

internal/refactor/inline/inline_test.go

@@ -401,6 +401,17 @@ func TestSubstitution(t *testing.T) {
 			`func _() { var local int; f(local) }`,
 			`func _() { var local int; _ = local }`,
 		},
+		{
+			"Regression test for detection of shadowing in nested functions.",
+			`func f(x int) { _ = func() { y := 1; print(y); print(x) } }`,
+			`func _(y int) { f(y) } `,
+			`func _(y int) {
+	{
+		var x int = y
+		_ = func() { y := 1; print(y); print(x) }
+	}
+}`,
+		},
 	})
 }