Allow a string argument to return(fail("Because!"));

Fixes #2694

bin/varnishtest/tests/v00040.vtc

@@ -14,9 +14,15 @@ client c1 {
 
 varnish v1 -errvcl {VCL "vcl2" Failed initialization} {
 	sub vcl_init {
-		return (fail);
+		return(fail("Do Not Press This Button Again"));
 	}
+	backend b1 { .host = "${s1_addr}"; }
+}
 
+varnish v1 -errvcl {Do Not Press} {
+	sub vcl_init {
+		return(fail("Do Not Press This Button Again"));
+	}
 	backend b1 { .host = "${s1_addr}"; }
 }
 

lib/libvcc/vcc_action.c

@@ -217,6 +217,22 @@ vcc_act_return_pass(struct vcc *tl)
 }
 /*--------------------------------------------------------------------*/
 
+static void
+vcc_act_return_fail(struct vcc *tl)
+{
+	ExpectErr(tl, '(');
+	vcc_NextToken(tl);
+	Fb(tl, 1, "VRT_fail(ctx,\n");
+	tl->indent += INDENT;
+	vcc_Expr(tl, STRING);
+	tl->indent -= INDENT;
+	ERRCHK(tl);
+	SkipToken(tl, ')');
+	Fb(tl, 1, ");\n");
+}
+
+/*--------------------------------------------------------------------*/
+
 static void
 vcc_act_return_synth(struct vcc *tl)
 {
@@ -321,6 +337,8 @@ vcc_act_return(struct vcc *tl, struct token *t, struct symbol *sym)
 			vcc_act_return_vcl(tl);
 		else if (hand == VCL_RET_PASS)
 			vcc_act_return_pass(tl);
+		else if (hand == VCL_RET_FAIL)
+			vcc_act_return_fail(tl);
 		else {
 			VSB_printf(tl->sb, "Arguments not allowed.\n");
 			vcc_ErrWhere(tl, tl->t);