cmd/compile/internal/types2: split out function instantiation from index expr

Also, factor out recording of type/value information after
evaluating an expression into an operand, so that we can
use it when handling instantiation expressions manually.

Change-Id: I6776e6cc243558079d6a203f2fe0a6ae0ecc33de
Reviewed-on: https://go-review.googlesource.com/c/go/+/308371
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/src/cmd/compile/internal/types2/index.go b/src/cmd/compile/internal/types2/index.go
index 0f4adab237..b9b5b53226 100644
--- a/src/cmd/compile/internal/types2/index.go
+++ b/src/cmd/compile/internal/types2/index.go
@@ -11,14 +11,18 @@ import (
 	"go/constant"
 )
 
-func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) {
+// If e is a valid function instantiation, indexExpr returns true.
+// In that case x represents the uninstantiated function value and
+// it is the caller's responsibility to instantiate the function.
+func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) (isFuncInst bool) {
 	check.exprOrType(x, e.X)
-	if x.mode == invalid {
+
+	switch x.mode {
+	case invalid:
 		check.use(e.Index)
 		return
-	}
 
-	if x.mode == typexpr {
+	case typexpr:
 		// type instantiation
 		x.mode = invalid
 		x.typ = check.varType(e)
@@ -26,13 +30,11 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) {
 			x.mode = typexpr
 		}
 		return
-	}
 
-	if x.mode == value {
+	case value:
 		if sig := asSignature(x.typ); sig != nil && len(sig.tparams) > 0 {
 			// function instantiation
-			check.funcInst(x, e)
-			return
+			return true
 		}
 	}
 
@@ -194,6 +196,7 @@ func (check *Checker) indexExpr(x *operand, e *syntax.IndexExpr) {
 	}
 
 	check.index(index, length)
+	return
 }
 
 func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {