[dev.typeparams] go/types: import predicates.go from dev.go2go

Changes from dev.go2go:
 + Update some isComparable cases to use the seen map.
 + Tiny updates to comments.

Change-Id: Iafd85d60835f17a87f514d9774cae07c183ee6cc
Reviewed-on: https://go-review.googlesource.com/c/go/+/278594
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>

1 files changed, 27 insertions, 17 deletions

diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index 51714790cb..c57edf8f0d 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -58,11 +58,16 @@ the type (and constant value, if any) is recorded via Info.Types, if present.
 
 type opPredicates map[token.Token]func(Type) bool
 
-var unaryOpPredicates = opPredicates{
-	token.ADD: isNumeric,
-	token.SUB: isNumeric,
-	token.XOR: isInteger,
-	token.NOT: isBoolean,
+var unaryOpPredicates opPredicates
+
+func init() {
+	// Setting unaryOpPredicates in init avoids declaration cycles.
+	unaryOpPredicates = opPredicates{
+		token.ADD: isNumeric,
+		token.SUB: isNumeric,
+		token.XOR: isInteger,
+		token.NOT: isBoolean,
+	}
 }
 
 func (check *Checker) op(m opPredicates, x *operand, op token.Token) bool {
@@ -785,20 +790,25 @@ func (check *Checker) shift(x, y *operand, e *ast.BinaryExpr, op token.Token) {
 	x.mode = value
 }
 
-var binaryOpPredicates = opPredicates{
-	token.ADD: func(typ Type) bool { return isNumeric(typ) || isString(typ) },
-	token.SUB: isNumeric,
-	token.MUL: isNumeric,
-	token.QUO: isNumeric,
-	token.REM: isInteger,
+var binaryOpPredicates opPredicates
+
+func init() {
+	// Setting binaryOpPredicates in init avoids declaration cycles.
+	binaryOpPredicates = opPredicates{
+		token.ADD: isNumericOrString,
+		token.SUB: isNumeric,
+		token.MUL: isNumeric,
+		token.QUO: isNumeric,
+		token.REM: isInteger,
 
-	token.AND:     isInteger,
-	token.OR:      isInteger,
-	token.XOR:     isInteger,
-	token.AND_NOT: isInteger,
+		token.AND:     isInteger,
+		token.OR:      isInteger,
+		token.XOR:     isInteger,
+		token.AND_NOT: isInteger,
 
-	token.LAND: isBoolean,
-	token.LOR:  isBoolean,
+		token.LAND: isBoolean,
+		token.LOR:  isBoolean,
+	}
 }
 
 // The binary expression e may be nil. It's passed in for better error messages only.