go/parser: fix ignored errors in ParseExprFrom

This CL fixes a bug in ParseExprFrom which makes
error messages ignored when there are 10+ errors
in a single expression.

fixes #34241
fixes #34274

Change-Id: I29a82d3e3e726279005eb6fbcd7ee3aebffaa679
Reviewed-on: https://go-review.googlesource.com/c/go/+/194638
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/parser/interface.go

@@ -173,7 +173,7 @@ func ParseDir(fset *token.FileSet, path string, filter func(os.FileInfo) bool, m
 // be a valid Go (type or value) expression. Specifically, fset must not
 // be nil.
 //
-func ParseExprFrom(fset *token.FileSet, filename string, src interface{}, mode Mode) (ast.Expr, error) {
+func ParseExprFrom(fset *token.FileSet, filename string, src interface{}, mode Mode) (expr ast.Expr, err error) {
 	if fset == nil {
 		panic("parser.ParseExprFrom: no token.FileSet provided (fset == nil)")
 	}

src/go/parser/parser_test.go

@@ -42,6 +42,22 @@ func nameFilter(filename string) bool {
 
 func dirFilter(f os.FileInfo) bool { return nameFilter(f.Name()) }
 
+func TestParseFile(t *testing.T) {
+	src := "package p\nvar _=s[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]"
+	_, err := ParseFile(token.NewFileSet(), "", src, 0)
+	if err == nil {
+		t.Errorf("ParseFile(%s) succeeded unexpectedly", src)
+	}
+}
+
+func TestParseExprFrom(t *testing.T) {
+	src := "s[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]+\ns[::]"
+	_, err := ParseExprFrom(token.NewFileSet(), "", src, 0)
+	if err == nil {
+		t.Errorf("ParseExprFrom(%s) succeeded unexpectedly", src)
+	}
+}
+
 func TestParseDir(t *testing.T) {
 	path := "."
 	pkgs, err := ParseDir(token.NewFileSet(), path, dirFilter, 0)