[dev.regabi] go/types: refuse excessively long constants

This is a port of CL 289049 to go/types. In that CL, tests were written
using the ability of tests/run.go to generate test packages dynamically.
For this CL, similar functionality is added to the go/types errmap
tests: tests are refactored to decouple the loading of source code from
the filesystem, so that tests for long constants may be generated
dynamically rather than checked-in as a large testdata file.

Change-Id: I92c7cb61a8d42c6593570ef7ae0af86b501fa34e
Reviewed-on: https://go-review.googlesource.com/c/go/+/290949
Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

2 files changed, 60 insertions, 31 deletions

diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 47d749b3a3..7292f7bcb2 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -68,11 +68,11 @@ func splitError(err error) (pos, msg string) {
 	return
 }
 
-func parseFiles(t *testing.T, filenames []string) ([]*ast.File, []error) {
+func parseFiles(t *testing.T, filenames []string, srcs [][]byte) ([]*ast.File, []error) {
 	var files []*ast.File
 	var errlist []error
-	for _, filename := range filenames {
-		file, err := parser.ParseFile(fset, filename, nil, parser.AllErrors)
+	for i, filename := range filenames {
+		file, err := parser.ParseFile(fset, filename, srcs[i], parser.AllErrors)
 		if file == nil {
 			t.Fatalf("%s: %s", filename, err)
 		}
@@ -101,19 +101,17 @@ var errRx = regexp.MustCompile(`^ *ERROR *(HERE)? *"?([^"]*)"?`)
 // errMap collects the regular expressions of ERROR comments found
 // in files and returns them as a map of error positions to error messages.
 //
-func errMap(t *testing.T, testname string, files []*ast.File) map[string][]string {
+// srcs must be a slice of the same length as files, containing the original
+// source for the parsed AST.
+func errMap(t *testing.T, files []*ast.File, srcs [][]byte) map[string][]string {
 	// map of position strings to lists of error message patterns
 	errmap := make(map[string][]string)
 
-	for _, file := range files {
-		filename := fset.Position(file.Package).Filename
-		src, err := os.ReadFile(filename)
-		if err != nil {
-			t.Fatalf("%s: could not read %s", testname, filename)
-		}
-
+	for i, file := range files {
+		tok := fset.File(file.Package)
+		src := srcs[i]
 		var s scanner.Scanner
-		s.Init(fset.AddFile(filename, -1, len(src)), src, nil, scanner.ScanComments)
+		s.Init(tok, 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
 
@@ -190,13 +188,13 @@ func eliminate(t *testing.T, errmap map[string][]string, errlist []error) {
 	}
 }
 
-func checkFiles(t *testing.T, sources []string) {
-	if len(sources) == 0 {
+func checkFiles(t *testing.T, filenames []string, srcs [][]byte) {
+	if len(filenames) == 0 {
 		t.Fatal("no source files")
 	}
 
 	// parse files and collect parser errors
-	files, errlist := parseFiles(t, sources)
+	files, errlist := parseFiles(t, filenames, srcs)
 
 	pkgName := "<no package>"
 	if len(files) > 0 {
@@ -214,11 +212,12 @@ func checkFiles(t *testing.T, sources []string) {
 	var conf Config
 
 	// special case for importC.src
-	if len(sources) == 1 && strings.HasSuffix(sources[0], "importC.src") {
-		conf.FakeImportC = true
+	if len(filenames) == 1 {
+		if strings.HasSuffix(filenames[0], "importC.src") {
+			conf.FakeImportC = true
+		}
 	}
-	// TODO(rFindley) we may need to use the source importer when adding generics
-	// tests.
+
 	conf.Importer = importer.Default()
 	conf.Error = func(err error) {
 		if *haltOnError {
@@ -253,7 +252,7 @@ func checkFiles(t *testing.T, sources []string) {
 
 	// match and eliminate errors;
 	// we are expecting the following errors
-	errmap := errMap(t, pkgName, files)
+	errmap := errMap(t, files, srcs)
 	eliminate(t, errmap, errlist)
 
 	// there should be no expected errors left
@@ -274,7 +273,13 @@ func TestCheck(t *testing.T) {
 	}
 	testenv.MustHaveGoBuild(t)
 	DefPredeclaredTestFuncs()
-	checkFiles(t, strings.Split(*testFiles, " "))
+	testPkg(t, strings.Split(*testFiles, " "))
+}
+
+func TestLongConstants(t *testing.T) {
+	format := "package longconst\n\nconst _ = %s\nconst _ = %s // ERROR excessively long constant"
+	src := fmt.Sprintf(format, strings.Repeat("1", 9999), strings.Repeat("1", 10001))
+	checkFiles(t, []string{"longconst.go"}, [][]byte{[]byte(src)})
 }
 
 func TestTestdata(t *testing.T)  { DefPredeclaredTestFuncs(); testDir(t, "testdata") }
@@ -293,26 +298,33 @@ func testDir(t *testing.T, dir string) {
 		path := filepath.Join(dir, fi.Name())
 
 		// if fi is a directory, its files make up a single package
-		var files []string
+		var filenames []string
 		if fi.IsDir() {
 			fis, err := ioutil.ReadDir(path)
 			if err != nil {
 				t.Error(err)
 				continue
 			}
-			files = make([]string, len(fis))
-			for i, fi := range fis {
-				// if fi is a directory, checkFiles below will complain
-				files[i] = filepath.Join(path, fi.Name())
-				if testing.Verbose() {
-					fmt.Printf("\t%s\n", files[i])
-				}
+			for _, fi := range fis {
+				filenames = append(filenames, filepath.Join(path, fi.Name()))
 			}
 		} else {
-			files = []string{path}
+			filenames = []string{path}
 		}
 		t.Run(filepath.Base(path), func(t *testing.T) {
-			checkFiles(t, files)
+			testPkg(t, filenames)
 		})
 	}
 }
+
+func testPkg(t *testing.T, filenames []string) {
+	srcs := make([][]byte, len(filenames))
+	for i, filename := range filenames {
+		src, err := os.ReadFile(filename)
+		if err != nil {
+			t.Fatalf("could not read %s: %v", filename, err)
+		}
+		srcs[i] = src
+	}
+	checkFiles(t, filenames, srcs)
+}
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 5e1fe28a43..1a3c486af7 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -1140,6 +1140,23 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 		goto Error
 
 	case *ast.BasicLit:
+		switch e.Kind {
+		case token.INT, token.FLOAT, token.IMAG:
+			// The max. mantissa precision for untyped numeric values
+			// is 512 bits, or 4048 bits for each of the two integer
+			// parts of a fraction for floating-point numbers that are
+			// represented accurately in the go/constant package.
+			// Constant literals that are longer than this many bits
+			// are not meaningful; and excessively long constants may
+			// consume a lot of space and time for a useless conversion.
+			// Cap constant length with a generous upper limit that also
+			// allows for separators between all digits.
+			const limit = 10000
+			if len(e.Value) > limit {
+				check.errorf(e, _InvalidConstVal, "excessively long constant: %s... (%d chars)", e.Value[:10], len(e.Value))
+				goto Error
+			}
+		}
 		x.setConst(e.Kind, e.Value)
 		if x.mode == invalid {
 			// The parser already establishes syntactic correctness.