internal/refactor/inline: freeishNames initial scope

Start the freeishNames walk with a non-nil scope. We may need it
if the argument node establishes a binding without first opening a
scope. (Example in the code.)

For golang/go#73321.

Change-Id: I72d45e26d27a726d869c9b8eb7d47bc187059832
Reviewed-on: https://go-review.googlesource.com/c/tools/+/665776
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: jba

internal/refactor/inline/free.go

@@ -35,7 +35,13 @@ import (
 //     panics if it sees one.
 func freeishNames(free map[string]bool, n ast.Node, includeComplitIdents bool) {
 	v := &freeVisitor{free: free, includeComplitIdents: includeComplitIdents}
+	// Begin with a scope, even though n might not be a form that establishes a scope.
+	// For example, n might be:
+	//    x := ...
+	// Then we need to add the first x to some scope.
+	v.openScope()
 	ast.Walk(v, n)
+	v.closeScope()
 	assert(v.scope == nil, "unbalanced scopes")
 }
 

internal/refactor/inline/free_test.go

@@ -229,6 +229,14 @@ func TestFreeishNames(t *testing.T) {
 	}
 }
 
+func TestFreeishNamesScope(t *testing.T) {
+	// Verify that inputs that don't start a scope don't crash.
+	_, f := mustParse(t, "free.go", `package p; func _() { x := 1; _ = x }`)
+	// Select the short var decl, not the entire function body.
+	n := f.Decls[0].(*ast.FuncDecl).Body.List[0]
+	freeishNames(map[string]bool{}, n, false)
+}
+
 func mustParse(t *testing.T, filename string, content any) (*token.FileSet, *ast.File) {
 	fset := token.NewFileSet()
 	f, err := parser.ParseFile(fset, filename, content, parser.ParseComments|parser.SkipObjectResolution)

internal/refactor/inline/testdata/n-ary.txtar

@@ -77,3 +77,28 @@ func _() {
 }
 
 func f4() int { return 2 + 2 }
+-- e/e.go --
+package e
+
+func _() {
+	switch {
+	case true:
+		a, b := f5() //@ inline(re"f5", f5)
+		_, _ = a, b
+	}
+}
+
+func f5() (int, int) { return 2, 2}
+
+-- f5 --
+package e
+
+func _() {
+	switch {
+	case true:
+		a, b := 2, 2 //@ inline(re"f5", f5)
+		_, _ = a, b
+	}
+}
+
+func f5() (int, int) { return 2, 2 }