[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>

1 files changed, 81 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/types2/version.go b/src/cmd/compile/internal/types2/version.go
new file mode 100644
index 0000000000..cb497f048e
--- /dev/null
+++ b/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]*)$`)