cmd/compile: disable Go1.13 language features for -lang=go1.12 and below

Fixes   #31747.
Updates #19308.
Updates #12711.
Updates #29008.
Updates #28493.
Updates #19113.

Change-Id: I76d2fdbc7698cc4e0f31b7ae24cbb4d28afbb6a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/174897
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/noder.go

@@ -1310,6 +1310,35 @@ func (p *noder) binOp(op syntax.Operator) Op {
 	return binOps[op]
 }
 
+// checkLangCompat reports an error if the representation of a numeric
+// literal is not compatible with the current language version.
+func checkLangCompat(lit *syntax.BasicLit) {
+	s := lit.Value
+	if len(s) <= 2 || langSupported(1, 13) {
+		return
+	}
+	// len(s) > 2
+	if strings.Contains(s, "_") {
+		yyerror("underscores in numeric literals only supported as of -lang=go1.13")
+		return
+	}
+	if s[0] != '0' {
+		return
+	}
+	base := s[1]
+	if base == 'b' || base == 'B' {
+		yyerror("binary literals only supported as of -lang=go1.13")
+		return
+	}
+	if base == 'o' || base == 'O' {
+		yyerror("0o/0O-style octal literals only supported as of -lang=go1.13")
+		return
+	}
+	if lit.Kind != syntax.IntLit && (base == 'x' || base == 'X') {
+		yyerror("hexadecimal floating-point literals only supported as of -lang=go1.13")
+	}
+}
+
 func (p *noder) basicLit(lit *syntax.BasicLit) Val {
 	// TODO: Don't try to convert if we had syntax errors (conversions may fail).
 	//       Use dummy values so we can continue to compile. Eventually, use a
@@ -1317,16 +1346,19 @@ func (p *noder) basicLit(lit *syntax.BasicLit) Val {
 	//       we can continue type-checking w/o spurious follow-up errors.
 	switch s := lit.Value; lit.Kind {
 	case syntax.IntLit:
+		checkLangCompat(lit)
 		x := new(Mpint)
 		x.SetString(s)
 		return Val{U: x}
 
 	case syntax.FloatLit:
+		checkLangCompat(lit)
 		x := newMpflt()
 		x.SetString(s)
 		return Val{U: x}
 
 	case syntax.ImagLit:
+		checkLangCompat(lit)
 		x := newMpcmplx()
 		x.Imag.SetString(strings.TrimSuffix(s, "i"))
 		return Val{U: x}

src/cmd/compile/internal/gc/typecheck.go

@@ -631,7 +631,11 @@ func typecheck1(n *Node, top int) (res *Node) {
 				n.Type = nil
 				return n
 			}
-
+			if t.IsSigned() && !langSupported(1, 13) {
+				yyerror("invalid operation: %v (signed shift count type %v, only supported as of -lang=go1.13)", n, r.Type)
+				n.Type = nil
+				return n
+			}
 			t = l.Type
 			if t != nil && t.Etype != TIDEAL && !t.IsInteger() {
 				yyerror("invalid operation: %v (shift of type %v)", n, t)

src/go/types/stdlib_test.go

@@ -180,6 +180,7 @@ 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)
 	)
 }
 

test/fixedbugs/issue31747.go

+// errorcheck -lang=go1.12
+
+// Copyright 2019 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 p
+
+// numeric literals
+const (
+	_ = 1_000 // ERROR "underscores in numeric literals only supported as of -lang=go1.13"
+	_ = 0b111 // ERROR "binary literals only supported as of -lang=go1.13"
+	_ = 0o567 // ERROR "0o/0O-style octal literals only supported as of -lang=go1.13"
+	_ = 0xabc // ok
+	_ = 0x0p1 // ERROR "hexadecimal floating-point literals only supported as of -lang=go1.13"
+
+	_ = 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 "signed shift count type int, only supported as of -lang=go1.13"
+	_ = 1 >> s // ERROR "signed shift count"
+)