1 files changed, 82 insertions, 0 deletions
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]*)$`)