go/types: sort unused declaration errors

By position, to ensure deterministic output.

Fixes #22525.

Change-Id: I28777d504a622416678b52afd6fc4c3ef32c12af
Reviewed-on: https://go-review.googlesource.com/75090
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/go/types/issues_test.go

@@ -292,3 +292,25 @@ func main() {
 	f("src1", src1)
 	f("src2", src2)
 }
+
+func TestIssue22525(t *testing.T) {
+	src := `package p; func f() { var a, b, c, d, e int }`
+	f, err := parser.ParseFile(fset, "", src, 0)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	got := "\n"
+	conf := Config{Error: func(err error) { got += err.Error() + "\n" }}
+	conf.Check(f.Name.Name, fset, []*ast.File{f}, nil) // do not crash
+	want := `
+1:27: a declared but not used
+1:30: b declared but not used
+1:33: c declared but not used
+1:36: d declared but not used
+1:39: e declared but not used
+`
+	if got != want {
+		t.Errorf("got: %swant: %s", got, want)
+	}
+}

src/go/types/stmt.go

@@ -11,6 +11,7 @@ import (
 	"go/ast"
 	"go/constant"
 	"go/token"
+	"sort"
 )
 
 func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body *ast.BlockStmt) {
@@ -57,11 +58,19 @@ func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body
 }
 
 func (check *Checker) usage(scope *Scope) {
-	for _, obj := range scope.elems {
-		if v, _ := obj.(*Var); v != nil && !v.used {
-			check.softErrorf(v.pos, "%s declared but not used", v.name)
+	var unused []*Var
+	for _, elem := range scope.elems {
+		if v, _ := elem.(*Var); v != nil && !v.used {
+			unused = append(unused, v)
 		}
 	}
+	sort.Slice(unused, func(i, j int) bool {
+		return unused[i].pos < unused[j].pos
+	})
+	for _, v := range unused {
+		check.softErrorf(v.pos, "%s declared but not used", v.name)
+	}
+
 	for _, scope := range scope.children {
 		check.usage(scope)
 	}