[dev.regabi] go/types: add support for language version checking

This is a port of CL 289509 to go/types. It differs from that CL in
codes added to errors, to fit the new factoring of check_test.go, and to
allow go/types to import regexp in deps_test.go

For #31793

Change-Id: Ia9e4c7f5aac1493001189184227c2ebc79a76e77
Reviewed-on: https://go-review.googlesource.com/c/go/+/291317
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

8 files changed, 186 insertions, 23 deletions

diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 02b29f498a..3fea5ecf0d 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -285,7 +285,7 @@ var depsRules = `
 	math/big, go/token
 	< go/constant;
 
-	container/heap, go/constant, go/parser
+	container/heap, go/constant, go/parser, regexp
 	< go/types;
 
 	FMT
diff --git a/src/go/types/api.go b/src/go/types/api.go
index d625959817..b5bbb2d97d 100644
--- a/src/go/types/api.go
+++ b/src/go/types/api.go
@@ -101,6 +101,13 @@ 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 it 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
diff --git a/src/go/types/check.go b/src/go/types/check.go
index 03798587e7..3bc8ee067c 100644
--- a/src/go/types/check.go
+++ b/src/go/types/check.go
@@ -8,6 +8,7 @@ package types
 
 import (
 	"errors"
+	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
@@ -84,10 +85,11 @@ type Checker struct {
 	fset *token.FileSet
 	pkg  *Package
 	*Info
-	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
-	posMap map[*Interface][]token.Pos // maps interface types to lists of embedded interface positions
-	pkgCnt map[string]int             // counts number of imported packages with a given name (for better error messages)
+	version version                    // accepted language version
+	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
+	posMap  map[*Interface][]token.Pos // maps interface types to lists of embedded interface positions
+	pkgCnt  map[string]int             // counts number of imported packages with a given name (for better error messages)
 
 	// information collected during type-checking of a set of package files
 	// (initialized by Files, valid only for the duration of check.Files;
@@ -176,15 +178,21 @@ func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Ch
 		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,
-		fset:   fset,
-		pkg:    pkg,
-		Info:   info,
-		objMap: make(map[Object]*declInfo),
-		impMap: make(map[importKey]*Package),
-		posMap: make(map[*Interface][]token.Pos),
-		pkgCnt: make(map[string]int),
+		conf:    conf,
+		fset:    fset,
+		pkg:     pkg,
+		Info:    info,
+		version: version,
+		objMap:  make(map[Object]*declInfo),
+		impMap:  make(map[importKey]*Package),
+		posMap:  make(map[*Interface][]token.Pos),
+		pkgCnt:  make(map[string]int),
 	}
 }
 
diff --git a/src/go/types/check_test.go b/src/go/types/check_test.go
index 7292f7bcb2..ca7d926ca9 100644
--- a/src/go/types/check_test.go
+++ b/src/go/types/check_test.go
@@ -47,7 +47,8 @@ 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\"")
 )
 
 var fset = token.NewFileSet()
@@ -188,7 +189,21 @@ func eliminate(t *testing.T, errmap map[string][]string, errlist []error) {
 	}
 }
 
-func checkFiles(t *testing.T, filenames []string, srcs [][]byte) {
+// 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, goVersion string, filenames []string, srcs [][]byte) {
 	if len(filenames) == 0 {
 		t.Fatal("no source files")
 	}
@@ -201,6 +216,11 @@ func checkFiles(t *testing.T, filenames []string, srcs [][]byte) {
 		pkgName = files[0].Name.Name
 	}
 
+	// 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 {
@@ -210,6 +230,7 @@ func checkFiles(t *testing.T, filenames []string, srcs [][]byte) {
 
 	// typecheck and collect typechecker errors
 	var conf Config
+	conf.GoVersion = goVersion
 
 	// special case for importC.src
 	if len(filenames) == 1 {
@@ -267,19 +288,20 @@ func checkFiles(t *testing.T, filenames []string, srcs [][]byte) {
 }
 
 // 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()
-	testPkg(t, strings.Split(*testFiles, " "))
+	testPkg(t, strings.Split(*testFiles, ","), *goVersion)
 }
 
 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)})
+	checkFiles(t, "", []string{"longconst.go"}, [][]byte{[]byte(src)})
 }
 
 func TestTestdata(t *testing.T)  { DefPredeclaredTestFuncs(); testDir(t, "testdata") }
@@ -312,12 +334,12 @@ func testDir(t *testing.T, dir string) {
 			filenames = []string{path}
 		}
 		t.Run(filepath.Base(path), func(t *testing.T) {
-			testPkg(t, filenames)
+			testPkg(t, filenames, "")
 		})
 	}
 }
 
-func testPkg(t *testing.T, filenames []string) {
+func testPkg(t *testing.T, filenames []string, goVersion string) {
 	srcs := make([][]byte, len(filenames))
 	for i, filename := range filenames {
 		src, err := os.ReadFile(filename)
@@ -326,5 +348,5 @@ func testPkg(t *testing.T, filenames []string) {
 		}
 		srcs[i] = src
 	}
-	checkFiles(t, filenames, srcs)
+	checkFiles(t, goVersion, filenames, srcs)
 }
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 7f8aaed411..aec3172327 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -772,6 +772,10 @@ func (check *Checker) shift(x, y *operand, e ast.Expr, op token.Token) {
 		check.invalidOp(y, _InvalidShiftCount, "shift count %s must be integer", y)
 		x.mode = invalid
 		return
+	} else if !isUnsigned(y.typ) && !check.allowVersion(check.pkg, 1, 13) {
+		check.invalidOp(y, _InvalidShiftCount, "signed shift count %s requires go1.13 or later", y)
+		x.mode = invalid
+		return
 	}
 
 	var yval constant.Value
@@ -1152,6 +1156,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 	case *ast.BasicLit:
 		switch e.Kind {
 		case token.INT, token.FLOAT, token.IMAG:
+			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
diff --git a/src/go/types/stdlib_test.go b/src/go/types/stdlib_test.go
index 71e14b85e5..979785de95 100644
--- a/src/go/types/stdlib_test.go
+++ b/src/go/types/stdlib_test.go
@@ -106,6 +106,7 @@ 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] {
@@ -115,13 +116,17 @@ 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):]
+					}
 				}
 			}
 		}
@@ -129,7 +134,7 @@ func testTestDir(t *testing.T, path string, ignore ...string) {
 		// parse and type-check file
 		file, err := parser.ParseFile(fset, filename, nil, 0)
 		if err == nil {
-			conf := Config{Importer: stdLibImporter}
+			conf := Config{GoVersion: goVersion, Importer: stdLibImporter}
 			_, err = conf.Check(filename, fset, []*ast.File{file}, nil)
 		}
 
@@ -180,7 +185,6 @@ 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)
 		"bug251.go",      // issue #34333 which was exposed with fix for #34151
 		"issue42058a.go", // go/types does not have constraints on channel element size
diff --git a/src/go/types/testdata/go1_12.src b/src/go/types/testdata/go1_12.src
new file mode 100644
index 0000000000..1e529f18be
--- /dev/null
+++ b/src/go/types/testdata/go1_12.src
@@ -0,0 +1,35 @@
+// 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"
+)
+
diff --git a/src/go/types/version.go b/src/go/types/version.go
new file mode 100644
index 0000000000..154694169b
--- /dev/null
+++ b/src/go/types/version.go
@@ -0,0 +1,82 @@
+// 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 types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"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 *ast.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, _InvalidLit, "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, _InvalidLit, "binary literals requires go1.13 or later")
+		return
+	}
+	if radix == 'o' || radix == 'O' {
+		check.errorf(lit, _InvalidLit, "0o/0O-style octal literals requires go1.13 or later")
+		return
+	}
+	if lit.Kind != token.INT && (radix == 'x' || radix == 'X') {
+		check.errorf(lit, _InvalidLit, "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]*)$`)