cmd/compile: disallow typed non-integer constant len and cap make arguments

make(T, n, m) returns a slice of type T with length n and capacity m
where "The size arguments n and m must be of integer type or untyped."
https://tip.golang.org/ref/spec#Making_slices_maps_and_channels

The failure to reject typed non-integer size arguments in make
during compile time was uncovered after https://golang.org/cl/27851
changed the generation of makeslice calls.

Fixes   #16940
Updates #16949

Change-Id: Ib1e3576f0e6ad199c9b16b7a50c2db81290c63b4
Reviewed-on: https://go-review.googlesource.com/28301Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -3754,6 +3754,11 @@ ret:
 }
 
 func checkmake(t *Type, arg string, n *Node) bool {
+	if !n.Type.IsInteger() && n.Type.Etype != TIDEAL {
+		Yyerror("non-integer %s argument in make(%v) - %v", arg, t, n.Type)
+		return false
+	}
+
 	if n.Op == OLITERAL {
 		switch n.Val().Ctype() {
 		case CTINT, CTRUNE, CTFLT, CTCPLX:
@@ -3779,11 +3784,6 @@ func checkmake(t *Type, arg string, n *Node) bool {
 		}
 	}
 
-	if !n.Type.IsInteger() && n.Type.Etype != TIDEAL {
-		Yyerror("non-integer %s argument in make(%v) - %v", arg, t, n.Type)
-		return false
-	}
-
 	// Defaultlit still necessary for non-constant: n might be 1<<k.
 	n = defaultlit(n, Types[TINT])
 

test/fixedbugs/issue16949.go

+// errorcheck
+
+// Copyright 2016 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.
+
+// Ensure that typed non-integer len and cap make arguments are not accepted.
+
+package main
+
+var sink []byte
+
+func main() {
+	sink = make([]byte, 1.0)
+	sink = make([]byte, float32(1.0)) // ERROR "non-integer.*len"
+	sink = make([]byte, float64(1.0)) // ERROR "non-integer.*len"
+
+	sink = make([]byte, 0, 1.0)
+	sink = make([]byte, 0, float32(1.0)) // ERROR "non-integer.*cap"
+	sink = make([]byte, 0, float64(1.0)) // ERROR "non-integer.*cap"
+
+	sink = make([]byte, 1+0i)
+	sink = make([]byte, complex64(1+0i))  // ERROR "non-integer.*len"
+	sink = make([]byte, complex128(1+0i)) // ERROR "non-integer.*len"
+
+	sink = make([]byte, 0, 1+0i)
+	sink = make([]byte, 0, complex64(1+0i))  // ERROR "non-integer.*cap"
+	sink = make([]byte, 0, complex128(1+0i)) // ERROR "non-integer.*cap"
+
+}