cmd/compile/internal/syntax: implement regression test harness for syntax errors

R=go1.11

Fixes #20800.

Change-Id: Ifea273521d42a543a43da2f655ace7c295650e30
Reviewed-on: https://go-review.googlesource.com/88335
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

3 files changed, 225 insertions, 0 deletions

diff --git a/src/cmd/compile/fmt_test.go b/src/cmd/compile/fmt_test.go
index 7342b5492b..ca6e6d0b69 100644
--- a/src/cmd/compile/fmt_test.go
+++ b/src/cmd/compile/fmt_test.go
@@ -656,6 +656,7 @@ var knownFormats = map[string]string{
 	"cmd/compile/internal/syntax.Node %T":             "",
 	"cmd/compile/internal/syntax.Operator %d":         "",
 	"cmd/compile/internal/syntax.Operator %s":         "",
+	"cmd/compile/internal/syntax.position %s":         "",
 	"cmd/compile/internal/syntax.token %d":            "",
 	"cmd/compile/internal/syntax.token %q":            "",
 	"cmd/compile/internal/syntax.token %s":            "",
diff --git a/src/cmd/compile/internal/syntax/error_test.go b/src/cmd/compile/internal/syntax/error_test.go
new file mode 100644
index 0000000000..72b1ad6333
--- /dev/null
+++ b/src/cmd/compile/internal/syntax/error_test.go
@@ -0,0 +1,191 @@
+// Copyright 2018 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 regression test harness for syntax errors.
+// The files in the testdata directory are parsed and the reported
+// errors are compared against the errors declared in those files.
+//
+// Errors are declared in place in the form of "error comments",
+// just before (or on the same line as) the offending token.
+//
+// Error comments must be of the form // ERROR rx or /* ERROR rx */
+// where rx is a regular expression that matches the reported error
+// message. The rx text comprises the comment text after "ERROR ",
+// with any white space around it stripped.
+//
+// If the line comment form is used, the reported error's line must
+// match the line of the error comment.
+//
+// If the regular comment form is used, the reported error's position
+// must match the position of the token immediately following the
+// error comment. Thus, /* ERROR ... */ comments should appear
+// immediately before the position where the error is reported.
+//
+// Currently, the test harness only supports one error comment per
+// token. If multiple error comments appear before a token, only
+// the last one is considered.
+
+package syntax
+
+import (
+	"flag"
+	"fmt"
+	"internal/testenv"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+	"testing"
+)
+
+const testdata = "testdata" // directory containing test files
+
+var print = flag.Bool("print", false, "only print errors")
+
+// A position represents a source position in the current file.
+type position struct {
+	line, col uint
+}
+
+func (pos position) String() string {
+	return fmt.Sprintf("%d:%d", pos.line, pos.col)
+}
+
+func sortedPositions(m map[position]string) []position {
+	list := make([]position, len(m))
+	i := 0
+	for pos := range m {
+		list[i] = pos
+		i++
+	}
+	sort.Slice(list, func(i, j int) bool {
+		a, b := list[i], list[j]
+		return a.line < b.line || a.line == b.line && a.col < b.col
+	})
+	return list
+}
+
+// declaredErrors returns a map of source positions to error
+// patterns, extracted from error comments in the given file.
+// Error comments in the form of line comments use col = 0
+// in their position.
+func declaredErrors(t *testing.T, filename string) map[position]string {
+	f, err := os.Open(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	declared := make(map[position]string)
+
+	var s scanner
+	var pattern string
+	s.init(f, func(line, col uint, msg string) {
+		// errors never start with '/' so they are automatically excluded here
+		switch {
+		case strings.HasPrefix(msg, "// ERROR "):
+			// we can't have another comment on the same line - just add it
+			declared[position{s.line, 0}] = strings.TrimSpace(msg[9:])
+		case strings.HasPrefix(msg, "/* ERROR "):
+			// we may have more comments before the next token - collect them
+			pattern = strings.TrimSpace(msg[9 : len(msg)-2])
+		}
+	}, comments)
+
+	// consume file
+	for {
+		s.next()
+		if pattern != "" {
+			declared[position{s.line, s.col}] = pattern
+			pattern = ""
+		}
+		if s.tok == _EOF {
+			break
+		}
+	}
+
+	return declared
+}
+
+func testSyntaxErrors(t *testing.T, filename string) {
+	declared := declaredErrors(t, filename)
+	if *print {
+		fmt.Println("Declared errors:")
+		for _, pos := range sortedPositions(declared) {
+			fmt.Printf("%s:%s: %s\n", filename, pos, declared[pos])
+		}
+
+		fmt.Println()
+		fmt.Println("Reported errors:")
+	}
+
+	f, err := os.Open(filename)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+
+	ParseFile(filename, func(err error) {
+		e, ok := err.(Error)
+		if !ok {
+			return
+		}
+
+		if *print {
+			fmt.Println(err)
+			return
+		}
+
+		orig := position{e.Pos.Line(), e.Pos.Col()}
+		pos := orig
+		pattern, found := declared[pos]
+		if !found {
+			// try line comment (only line must match)
+			pos = position{e.Pos.Line(), 0}
+			pattern, found = declared[pos]
+		}
+		if found {
+			rx, err := regexp.Compile(pattern)
+			if err != nil {
+				t.Errorf("%s: %v", pos, err)
+				return
+			}
+			if match := rx.MatchString(e.Msg); !match {
+				t.Errorf("%s: %q does not match %q", pos, e.Msg, pattern)
+				return
+			}
+			// we have a match - eliminate this error
+			delete(declared, pos)
+		} else {
+			t.Errorf("%s: unexpected error: %s", orig, e.Msg)
+		}
+	}, nil, 0)
+
+	if *print {
+		fmt.Println()
+		return // we're done
+	}
+
+	// report expected but not reported errors
+	for pos, pattern := range declared {
+		t.Errorf("%s: missing error: %s", pos, pattern)
+	}
+}
+
+func TestSyntaxErrors(t *testing.T) {
+	testenv.MustHaveGoBuild(t) // we need access to source (testdata)
+
+	list, err := ioutil.ReadDir(testdata)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, fi := range list {
+		name := fi.Name()
+		if !fi.IsDir() && !strings.HasPrefix(name, ".") {
+			testSyntaxErrors(t, filepath.Join(testdata, name))
+		}
+	}
+}
diff --git a/src/cmd/compile/internal/syntax/testdata/sample.src b/src/cmd/compile/internal/syntax/testdata/sample.src
new file mode 100644
index 0000000000..5a2b4bf0c4
--- /dev/null
+++ b/src/cmd/compile/internal/syntax/testdata/sample.src
@@ -0,0 +1,33 @@
+// Copyright 2018 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 is a sample test file illustrating the use
+// of error comments with the error test harness.
+
+package p
+
+// The following are invalid error comments; they are
+// silently ignored. The prefix must be exactly one of
+// "/* ERROR " or "// ERROR ".
+//
+/*ERROR*/
+/*ERROR foo*/
+/* ERRORfoo */
+/*  ERROR foo */
+//ERROR
+// ERROR
+// ERRORfoo
+//  ERROR foo
+
+// This is a valid error comment; it applies to the
+// immediately following token. 
+import "math" /* ERROR unexpected comma */ ,
+
+// If there are multiple /*-style error comments before
+// the next token, only the last one is considered.
+type x = /* ERROR ignored */ /* ERROR literal 0 in type declaration */ 0
+
+// A //-style error comment matches any error position
+// on the same line.
+func () foo() // ERROR method has no receiver