[dev.typeparams] cmd/compile/internal/types2: add support for language version checking

Add the Config.Lang field which may be set to a Go version string,
such as "go1.12". This is a string rather than explicit semantic
version numbers (such as {1, 12}) for API robustness; a string
is more flexible should we need more or different information.

Add -lang flag to types2 package for use with (manual) testing
when running "go test -run Check$ -lang=... -files=...".

While changing flags, look for comma-separated (rather than space-
separated) files when providing the -file flag.

Check that numeric constant literals, signed shift counts are
accepted according to the selected language version.

Type alias declarations and overlapping embedded interfaces are
not yet checked.

Updates #31793.

Change-Id: I9ff238ed38a88f377eb2267dc3e8816b89a40635
Reviewed-on: https://go-review.googlesource.com/c/go/+/289509
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/api.go

@@ -99,6 +99,13 @@ type ImporterFrom interface {
 // A Config specifies the configuration for type checking.
 // The zero value for Config is a ready-to-use default configuration.
 type Config struct {
+	// GoVersion describes the accepted Go language version. The string
+	// must follow the format "go%d.%d" (e.g. "go1.12") or ist must be
+	// empty; an empty string indicates the latest language version.
+	// If the format is invalid, invoking the type checker will cause a
+	// panic.
+	GoVersion string
+
 	// If IgnoreFuncBodies is set, function bodies are not
 	// type-checked.
 	IgnoreFuncBodies bool

src/cmd/compile/internal/types2/check.go

@@ -88,6 +88,7 @@ type Checker struct {
 	conf *Config
 	pkg  *Package
 	*Info
+	version version                     // accepted language version
 	nextId  uint64                      // unique Id for type parameters (first valid Id is 1)
 	objMap  map[Object]*declInfo        // maps package-level objects and (non-interface) methods to declaration info
 	impMap  map[importKey]*Package      // maps (import path, source directory) to (complete or fake) package
@@ -182,10 +183,16 @@ func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
 		info = new(Info)
 	}
 
+	version, err := parseGoVersion(conf.GoVersion)
+	if err != nil {
+		panic(fmt.Sprintf("invalid Go version %q (%v)", conf.GoVersion, err))
+	}
+
 	return &Checker{
 		conf:    conf,
 		pkg:     pkg,
 		Info:    info,
+		version: version,
 		nextId:  1,
 		objMap:  make(map[Object]*declInfo),
 		impMap:  make(map[importKey]*Package),

src/cmd/compile/internal/types2/check_test.go

@@ -44,7 +44,8 @@ import (
 var (
 	haltOnError = flag.Bool("halt", false, "halt on error")
 	listErrors  = flag.Bool("errlist", false, "list errors")
-	testFiles   = flag.String("files", "", "space-separated list of test files")
+	testFiles   = flag.String("files", "", "comma-separated list of test files")
+	goVersion   = flag.String("lang", "", "Go language version (e.g. \"go1.12\"")
 )
 
 func parseFiles(t *testing.T, filenames []string, mode syntax.Mode) ([]*syntax.File, []error) {
@@ -83,7 +84,21 @@ func delta(x, y uint) uint {
 	}
 }
 
-func checkFiles(t *testing.T, sources []string, colDelta uint, trace bool) {
+// goVersionRx matches a Go version string using '_', e.g. "go1_12".
+var goVersionRx = regexp.MustCompile(`^go[1-9][0-9]*_(0|[1-9][0-9]*)$`)
+
+// asGoVersion returns a regular Go language version string
+// if s is a Go version string using '_' rather than '.' to
+// separate the major and minor version numbers (e.g. "go1_12").
+// Otherwise it returns the empty string.
+func asGoVersion(s string) string {
+	if goVersionRx.MatchString(s) {
+		return strings.Replace(s, "_", ".", 1)
+	}
+	return ""
+}
+
+func checkFiles(t *testing.T, sources []string, goVersion string, colDelta uint, trace bool) {
 	if len(sources) == 0 {
 		t.Fatal("no source files")
 	}
@@ -100,6 +115,11 @@ func checkFiles(t *testing.T, sources []string, colDelta uint, trace bool) {
 		pkgName = files[0].PkgName.Value
 	}
 
+	// if no Go version is given, consider the package name
+	if goVersion == "" {
+		goVersion = asGoVersion(pkgName)
+	}
+
 	if *listErrors && len(errlist) > 0 {
 		t.Errorf("--- %s:", pkgName)
 		for _, err := range errlist {
@@ -109,6 +129,7 @@ func checkFiles(t *testing.T, sources []string, colDelta uint, trace bool) {
 
 	// typecheck and collect typechecker errors
 	var conf Config
+	conf.GoVersion = goVersion
 	conf.AcceptMethodTypeParams = true
 	conf.InferFromConstraints = true
 	// special case for importC.src
@@ -220,13 +241,14 @@ func checkFiles(t *testing.T, sources []string, colDelta uint, trace bool) {
 }
 
 // TestCheck is for manual testing of selected input files, provided with -files.
+// The accepted Go language version can be controlled with the -lang flag.
 func TestCheck(t *testing.T) {
 	if *testFiles == "" {
 		return
 	}
 	testenv.MustHaveGoBuild(t)
 	DefPredeclaredTestFuncs()
-	checkFiles(t, strings.Split(*testFiles, " "), 0, testing.Verbose())
+	checkFiles(t, strings.Split(*testFiles, ","), *goVersion, 0, testing.Verbose())
 }
 
 func TestTestdata(t *testing.T)  { DefPredeclaredTestFuncs(); testDir(t, 75, "testdata") } // TODO(gri) narrow column tolerance
@@ -263,7 +285,7 @@ func testDir(t *testing.T, colDelta uint, dir string) {
 					fmt.Printf("\t%s\n", files[i])
 				}
 			}
-			checkFiles(t, files, colDelta, false)
+			checkFiles(t, files, "", colDelta, false)
 			continue
 		}
 
@@ -271,6 +293,6 @@ func testDir(t *testing.T, colDelta uint, dir string) {
 		if testing.Verbose() {
 			fmt.Printf("%3d %s\n", count, path)
 		}
-		checkFiles(t, []string{path}, colDelta, false)
+		checkFiles(t, []string{path}, "", colDelta, false)
 	}
 }

src/cmd/compile/internal/types2/expr.go

@@ -816,6 +816,10 @@ func (check *Checker) shift(x, y *operand, e syntax.Expr, op syntax.Operator) {
 		check.invalidOpf(y, "shift count %s must be integer", y)
 		x.mode = invalid
 		return
+	} else if !isUnsigned(y.typ) && !check.allowVersion(check.pkg, 1, 13) {
+		check.invalidOpf(y, "signed shift count %s requires go1.13 or later", y)
+		x.mode = invalid
+		return
 	}
 
 	if x.mode == constant_ {
@@ -1185,6 +1189,7 @@ func (check *Checker) exprInternal(x *operand, e syntax.Expr, hint Type) exprKin
 		}
 		switch e.Kind {
 		case syntax.IntLit, syntax.FloatLit, syntax.ImagLit:
+			check.langCompat(e)
 			// 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

src/cmd/compile/internal/types2/stdlib_test.go

@@ -110,6 +110,7 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		// get per-file instructions
 		expectErrors := false
 		filename := filepath.Join(path, f.Name())
+		goVersion := ""
 		if comment := firstComment(filename); comment != "" {
 			fields := strings.Fields(comment)
 			switch fields[0] {
@@ -119,13 +120,17 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 				expectErrors = true
 				for _, arg := range fields[1:] {
 					if arg == "-0" || arg == "-+" || arg == "-std" {
-						// Marked explicitly as not expected errors (-0),
+						// Marked explicitly as not expecting errors (-0),
 						// or marked as compiling runtime/stdlib, which is only done
 						// to trigger runtime/stdlib-only error output.
 						// In both cases, the code should typecheck.
 						expectErrors = false
 						break
 					}
+					const prefix = "-lang="
+					if strings.HasPrefix(arg, prefix) {
+						goVersion = arg[len(prefix):]
+					}
 				}
 			}
 		}
@@ -136,7 +141,7 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		}
 		file, err := syntax.ParseFile(filename, nil, nil, 0)
 		if err == nil {
-			conf := Config{Importer: stdLibImporter}
+			conf := Config{GoVersion: goVersion, Importer: stdLibImporter}
 			_, err = conf.Check(filename, []*syntax.File{file}, nil)
 		}
 
@@ -187,7 +192,6 @@ func TestStdFixed(t *testing.T) {
 		"issue22200b.go", // go/types does not have constraints on stack size
 		"issue25507.go",  // go/types does not have constraints on stack size
 		"issue20780.go",  // go/types does not have constraints on stack size
-		"issue31747.go",  // go/types does not have constraints on language level (-lang=go1.12) (see #31793)
 		"issue34329.go",  // go/types does not have constraints on language level (-lang=go1.13) (see #31793)
 		"issue42058a.go", // go/types does not have constraints on channel element size
 		"issue42058b.go", // go/types does not have constraints on channel element size

src/cmd/compile/internal/types2/testdata/go1_12.src

@@ -0,0 +1,34 @@
+// Copyright 2021 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.
+
+// Check Go language version-specific errors.
+
+package go1_12 // go1.12
+
+// numeric literals
+const (
+	_ = 1_000 // ERROR "underscores in numeric literals requires go1.13 or later"
+	_ = 0b111 // ERROR "binary literals requires go1.13 or later"
+	_ = 0o567 // ERROR "0o/0O-style octal literals requires go1.13 or later"
+	_ = 0xabc // ok
+	_ = 0x0p1 // ERROR "hexadecimal floating-point literals requires go1.13 or later"
+
+	_ = 0B111 // ERROR "binary"
+	_ = 0O567 // ERROR "octal"
+	_ = 0Xabc // ok
+	_ = 0X0P1 // ERROR "hexadecimal floating-point"
+
+	_ = 1_000i // ERROR "underscores"
+	_ = 0b111i // ERROR "binary"
+	_ = 0o567i // ERROR "octal"
+	_ = 0xabci // ERROR "hexadecimal floating-point"
+	_ = 0x0p1i // ERROR "hexadecimal floating-point"
+)
+
+// signed shift counts
+var (
+	s int
+	_ = 1 << s // ERROR "invalid operation: signed shift count s \(variable of type int\) requires go1.13 or later"
+	_ = 1 >> s // ERROR "signed shift count"
+)

src/cmd/compile/internal/types2/version.go

@@ -0,0 +1,81 @@
+// Copyright 2021 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.
+
+package types2
+
+import (
+	"cmd/compile/internal/syntax"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// langCompat reports an error if the representation of a numeric
+// literal is not compatible with the current language version.
+func (check *Checker) langCompat(lit *syntax.BasicLit) {
+	s := lit.Value
+	if len(s) <= 2 || check.allowVersion(check.pkg, 1, 13) {
+		return
+	}
+	// len(s) > 2
+	if strings.Contains(s, "_") {
+		check.errorf(lit, "underscores in numeric literals requires go1.13 or later")
+		return
+	}
+	if s[0] != '0' {
+		return
+	}
+	radix := s[1]
+	if radix == 'b' || radix == 'B' {
+		check.errorf(lit, "binary literals requires go1.13 or later")
+		return
+	}
+	if radix == 'o' || radix == 'O' {
+		check.errorf(lit, "0o/0O-style octal literals requires go1.13 or later")
+		return
+	}
+	if lit.Kind != syntax.IntLit && (radix == 'x' || radix == 'X') {
+		check.errorf(lit, "hexadecimal floating-point literals requires go1.13 or later")
+	}
+}
+
+// allowVersion reports whether the given package
+// is allowed to use version major.minor.
+func (check *Checker) allowVersion(pkg *Package, major, minor int) bool {
+	// We assume that imported packages have all been checked,
+	// so we only have to check for the local package.
+	if pkg != check.pkg {
+		return true
+	}
+	ma, mi := check.version.major, check.version.minor
+	return ma == 0 && mi == 0 || ma > major || ma == major && mi >= minor
+}
+
+type version struct {
+	major, minor int
+}
+
+// parseGoVersion parses a Go version string (such as "go1.12")
+// and returns the version, or an error. If s is the empty
+// string, the version is 0.0.
+func parseGoVersion(s string) (v version, err error) {
+	if s == "" {
+		return
+	}
+	matches := goVersionRx.FindStringSubmatch(s)
+	if matches == nil {
+		err = fmt.Errorf(`should be something like "go1.12"`)
+		return
+	}
+	v.major, err = strconv.Atoi(matches[1])
+	if err != nil {
+		return
+	}
+	v.minor, err = strconv.Atoi(matches[2])
+	return
+}
+
+// goVersionRx matches a Go version string, e.g. "go1.12".
+var goVersionRx = regexp.MustCompile(`^go([1-9][0-9]*)\.(0|[1-9][0-9]*)$`)