1 files changed, 202 insertions, 0 deletions
diff --git a/src/go/parser/error_test.go b/src/go/parser/error_test.go
new file mode 100644
index 0000000..a4e17dd
--- /dev/null
+++ b/src/go/parser/error_test.go
@@ -0,0 +1,202 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a parser test harness. The files in the testdata
+// directory are parsed and the errors reported are compared against the
+// error messages expected in the test files. The test files must end in
+// .src rather than .go so that they are not disturbed by gofmt runs.
+//
+// Expected errors are indicated in the test files by putting a comment
+// of the form /* ERROR "rx" */ immediately following an offending token.
+// The harness will verify that an error matching the regular expression
+// rx is reported at that source position.
+//
+// For instance, the following test file indicates that a "not declared"
+// error should be reported for the undeclared variable x:
+//
+//	package p
+//	func f() {
+//		_ = x /* ERROR "not declared" */ + 1
+//	}
+
+package parser
+
+import (
+	"flag"
+	"go/scanner"
+	"go/token"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+var traceErrs = flag.Bool("trace_errs", false, "whether to enable tracing for error tests")
+
+const testdata = "testdata"
+
+// getFile assumes that each filename occurs at most once
+func getFile(fset *token.FileSet, filename string) (file *token.File) {
+	fset.Iterate(func(f *token.File) bool {
+		if f.Name() == filename {
+			if file != nil {
+				panic(filename + " used multiple times")
+			}
+			file = f
+		}
+		return true
+	})
+	return file
+}
+
+func getPos(fset *token.FileSet, filename string, offset int) token.Pos {
+	if f := getFile(fset, filename); f != nil {
+		return f.Pos(offset)
+	}
+	return token.NoPos
+}
+
+// ERROR comments must be of the form /* ERROR "rx" */ and rx is
+// a regular expression that matches the expected error message.
+// The special form /* ERROR HERE "rx" */ must be used for error
+// messages that appear immediately after a token, rather than at
+// a token's position, and ERROR AFTER means after the comment
+// (e.g. at end of line).
+var errRx = regexp.MustCompile(`^/\* *ERROR *(HERE|AFTER)? *"([^"]*)" *\*/$`)
+
+// expectedErrors collects the regular expressions of ERROR comments found
+// in files and returns them as a map of error positions to error messages.
+func expectedErrors(fset *token.FileSet, filename string, src []byte) map[token.Pos]string {
+	errors := make(map[token.Pos]string)
+
+	var s scanner.Scanner
+	// file was parsed already - do not add it again to the file
+	// set otherwise the position information returned here will
+	// not match the position information collected by the parser
+	s.Init(getFile(fset, filename), src, nil, scanner.ScanComments)
+	var prev token.Pos // position of last non-comment, non-semicolon token
+	var here token.Pos // position immediately after the token at position prev
+
+	for {
+		pos, tok, lit := s.Scan()
+		switch tok {
+		case token.EOF:
+			return errors
+		case token.COMMENT:
+			s := errRx.FindStringSubmatch(lit)
+			if len(s) == 3 {
+				if s[1] == "HERE" {
+					pos = here // start of comment
+				} else if s[1] == "AFTER" {
+					pos += token.Pos(len(lit)) // end of comment
+				} else {
+					pos = prev // token prior to comment
+				}
+				errors[pos] = s[2]
+			}
+		case token.SEMICOLON:
+			// don't use the position of auto-inserted (invisible) semicolons
+			if lit != ";" {
+				break
+			}
+			fallthrough
+		default:
+			prev = pos
+			var l int // token length
+			if tok.IsLiteral() {
+				l = len(lit)
+			} else {
+				l = len(tok.String())
+			}
+			here = prev + token.Pos(l)
+		}
+	}
+}
+
+// compareErrors compares the map of expected error messages with the list
+// of found errors and reports discrepancies.
+func compareErrors(t *testing.T, fset *token.FileSet, expected map[token.Pos]string, found scanner.ErrorList) {
+	t.Helper()
+	for _, error := range found {
+		// error.Pos is a token.Position, but we want
+		// a token.Pos so we can do a map lookup
+		pos := getPos(fset, error.Pos.Filename, error.Pos.Offset)
+		if msg, found := expected[pos]; found {
+			// we expect a message at pos; check if it matches
+			rx, err := regexp.Compile(msg)
+			if err != nil {
+				t.Errorf("%s: %v", error.Pos, err)
+				continue
+			}
+			if match := rx.MatchString(error.Msg); !match {
+				t.Errorf("%s: %q does not match %q", error.Pos, error.Msg, msg)
+				continue
+			}
+			// we have a match - eliminate this error
+			delete(expected, pos)
+		} else {
+			// To keep in mind when analyzing failed test output:
+			// If the same error position occurs multiple times in errors,
+			// this message will be triggered (because the first error at
+			// the position removes this position from the expected errors).
+			t.Errorf("%s: unexpected error: %s", error.Pos, error.Msg)
+		}
+	}
+
+	// there should be no expected errors left
+	if len(expected) > 0 {
+		t.Errorf("%d errors not reported:", len(expected))
+		for pos, msg := range expected {
+			t.Errorf("%s: %s\n", fset.Position(pos), msg)
+		}
+	}
+}
+
+func checkErrors(t *testing.T, filename string, input any, mode Mode, expectErrors bool) {
+	t.Helper()
+	src, err := readSource(filename, input)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	fset := token.NewFileSet()
+	_, err = ParseFile(fset, filename, src, mode)
+	found, ok := err.(scanner.ErrorList)
+	if err != nil && !ok {
+		t.Error(err)
+		return
+	}
+	found.RemoveMultiples()
+
+	expected := map[token.Pos]string{}
+	if expectErrors {
+		// we are expecting the following errors
+		// (collect these after parsing a file so that it is found in the file set)
+		expected = expectedErrors(fset, filename, src)
+	}
+
+	// verify errors returned by the parser
+	compareErrors(t, fset, expected, found)
+}
+
+func TestErrors(t *testing.T) {
+	list, err := os.ReadDir(testdata)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, d := range list {
+		name := d.Name()
+		t.Run(name, func(t *testing.T) {
+			if !d.IsDir() && !strings.HasPrefix(name, ".") && (strings.HasSuffix(name, ".src") || strings.HasSuffix(name, ".go2")) {
+				mode := DeclarationErrors | AllErrors
+				if *traceErrs {
+					mode |= Trace
+				}
+				checkErrors(t, filepath.Join(testdata, name), nil, mode, true)
+			}
+		})
+	}
+}