cmd/compile/internal/syntax: add "~" operator

Change-Id: I7991103d97b97260d9615b7f5baf7ec75ad87d1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/307370
Trust: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: griesemer

src/cmd/compile/internal/syntax/operator_string.go

@@ -343,6 +343,11 @@ redo:
 		s.op, s.prec = Not, 0
 		s.tok = _Operator
 
+	case '~':
+		s.nextch()
+		s.op, s.prec = Tilde, 0
+		s.tok = _Operator
+
 	default:
 		s.errorf("invalid character %#U", s.ch)
 		s.nextch()

src/cmd/compile/internal/syntax/scanner.go

@@ -232,6 +232,9 @@ var sampleTokens = [...]struct {
 	{_Literal, "`\r`", 0, 0},
 
 	// operators
+	{_Operator, "!", Not, 0},
+	{_Operator, "~", Tilde, 0},
+
 	{_Operator, "||", OrOr, precOrOr},
 
 	{_Operator, "&&", AndAnd, precAndAnd},
@@ -601,7 +604,7 @@ func TestScanErrors(t *testing.T) {
 		{"\U0001d7d8" /* 𝟘 */, "identifier cannot begin with digit U+1D7D8 '𝟘'", 0, 0},
 		{"foo\U0001d7d8_½" /* foo𝟘_½ */, "invalid character U+00BD '½' in identifier", 0, 8 /* byte offset */},
 
-		{"x + ~y", "invalid character U+007E '~'", 0, 4},
+		{"x + #y", "invalid character U+0023 '#'", 0, 4},
 		{"foo$bar = 0", "invalid character U+0024 '$'", 0, 3},
 		{"0123456789", "invalid digit '8' in octal literal", 0, 8},
 		{"0123456789. /* foobar", "comment not terminated", 0, 12},   // valid float constant

src/cmd/compile/internal/syntax/scanner_test.go

@@ -111,9 +111,10 @@ const (
 	_ Operator = iota
 
 	// Def is the : in :=
-	Def  // :
-	Not  // !
-	Recv // <-
+	Def   // :
+	Not   // !
+	Recv  // <-
+	Tilde // ~
 
 	// precOrOr
 	OrOr // ||

src/cmd/compile/internal/syntax/tokens.go

@@ -6,7 +6,10 @@
 
 package p
 
-func f(x int) {
-	_ = ~x    // ERROR "invalid character"
-	_ = x ~ x // ERROR "invalid character" "unexpected x at end of statement"
+func _(x int) {
+	_ = ~x    // ERROR "unexpected ~"
+}
+
+func _(x int) {
+	_ = x ~ x // ERROR "unexpected ~ at end of statement"
 }