cmd/gc: missing type inference for untyped complex() calls.

Fixes #5014.

R=golang-dev, r, rsc, daniel.morsing
CC=golang-dev
https://golang.org/cl/7664043

src/cmd/gc/const.c

@@ -119,6 +119,27 @@ convlit1(Node **np, Type *t, int explicit)
 		}
 		n->type = t;
 		return;
+	case OCOMPLEX:
+		if(n->type->etype == TIDEAL) {
+			switch(t->etype) {
+			default:
+				// If trying to convert to non-complex type,
+				// leave as complex128 and let typechecker complain.
+				t = types[TCOMPLEX128];
+				//fallthrough
+			case TCOMPLEX128:
+				n->type = t;
+				convlit(&n->left, types[TFLOAT64]);
+				convlit(&n->right, types[TFLOAT64]);
+				break;
+			case TCOMPLEX64:
+				n->type = t;
+				convlit(&n->left, types[TFLOAT32]);
+				convlit(&n->right, types[TFLOAT32]);
+				break;
+			}
+		}
+		return;
 	}
 
 	// avoided repeated calculations, errors
@@ -1068,6 +1089,11 @@ idealkind(Node *n)
 			return k1;
 		else
 			return k2;
+	case OREAL:
+	case OIMAG:
+		return CTFLT;
+	case OCOMPLEX:
+		return CTCPLX;
 	case OADDSTR:
 		return CTSTR;
 	case OANDAND:

src/cmd/gc/typecheck.c

@@ -1180,16 +1180,18 @@ reswitch:
 		if(l->type == T || r->type == T)
 			goto error;
 		defaultlit2(&l, &r, 0);
+		if(l->type == T || r->type == T)
+			goto error;
 		n->left = l;
 		n->right = r;
 		if(!eqtype(l->type, r->type)) {
-		badcmplx:
 			yyerror("invalid operation: %N (mismatched types %T and %T)", n, l->type, r->type);
 			goto error;
 		}
 		switch(l->type->etype) {
 		default:
-			goto badcmplx;
+			yyerror("invalid operation: %N (arguments have type %T, expected floating-point)", n, l->type, r->type);
+			goto error;
 		case TIDEAL:
 			t = types[TIDEAL];
 			break;

test/shift1.go

@@ -42,4 +42,16 @@ var (
 	a3 = 1.0<<s + 0 // ERROR "invalid operation|shift of non-integer operand"
 	// issue 4937
 	b3 = 1<<s + 1 + 1.0 // ERROR "invalid operation|shift of non-integer operand"
+	// issue 5014
+	c3     = complex(1<<s, 0) // ERROR "shift of type float64"
+	d3 int = complex(1<<s, 3) // ERROR "cannot use.*as type int" "shift of type float64"
+	e3     = real(1 << s)     // ERROR "invalid"
+	f3     = imag(1 << s)     // ERROR "invalid"
+)
+
+var (
+	a4 float64
+	b4 int
+	c4 = complex(1<<s, a4) // ERROR "shift of type float64"
+	d4 = complex(1<<s, b4) // ERROR "invalid"
 )