FIX: better struct! initialization; empty struct not allowed

Author: Oldes

src/core/t-struct.c

@@ -686,7 +686,7 @@ static REBOOL parse_field_type(struct Struct_Field *field, REBVAL *spec, REBVAL
 /*
  * Format:
  * make struct! [
- *     field1 [type1]
+ *     field1  [type1]
  *     field2: [type2] field2-init-value
  * 	   field3: [struct [field1 [type1]]] field3-init-struct-value
  * 	   field4: [type1[3]] field4-init-block-value
@@ -695,10 +695,17 @@ static REBOOL parse_field_type(struct Struct_Field *field, REBVAL *spec, REBVAL
 ***********************************************************************/
 {
 	//RL_Print("%s\n", __func__);
-	REBINT max_fields = 16;
+	
 	if (!IS_BLOCK(data)) return FALSE; // validate early!
-
-	VAL_STRUCT_FIELDS(out) = Make_Series(max_fields, sizeof(struct Struct_Field), FALSE);
+	
+	/* Using spec block length as a prediction of fields number
+	   (each field requires at least 2 spec values)	*/
+	REBCNT num_spec_values = VAL_TAIL(data) - VAL_INDEX(data);
+	REBCNT min_fileds = num_spec_values >> 1;
+	/* Don't allow empty struct! */
+	if (min_fileds == 0) Trap_Arg(data);
+	
+	VAL_STRUCT_FIELDS(out) = Make_Series(min_fileds, sizeof(struct Struct_Field), FALSE);
 	BARE_SERIES(VAL_STRUCT_FIELDS(out));
 
 	//Reduce_Block_No_Set(VAL_SERIES(data), 0, NULL);
@@ -718,7 +725,8 @@ static REBOOL parse_field_type(struct Struct_Field *field, REBVAL *spec, REBVAL
 	EXPAND_SERIES_TAIL(VAL_STRUCT_DATA(out), 1);
 	BARE_SERIES(VAL_STRUCT_DATA(out));
 
-	VAL_STRUCT_DATA_BIN(out) = Make_Series(max_fields << 2, 1, FALSE);
+	/* one byte per field as a minimum (expands when needed) */
+	VAL_STRUCT_DATA_BIN(out) = Make_Series(min_fileds, 1, FALSE);
 	BARE_SERIES(VAL_STRUCT_DATA_BIN(out));
 	VAL_STRUCT_OFFSET(out) = 0;
 

src/tests/units/struct-test.r3

@@ -133,6 +133,15 @@ Rebol [
 	--assert all [s2/a = 1  s2/b = 20]
 	--assert all [s3/a = 10 s3/b = 20]
 
+--test-- "Struct with many fields"
+	blk: copy []
+	repeat i 32 [repend blk [to word! join 'a i [int8!]]]
+	--assert all [
+		not error? try [s: make struct! blk]
+		[a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 a11 a12 a13 a14 a15 a16 a17 a18 a19 a20 a21 a22 a23 a24 a25 a26 a27 a28 a29 a30 a31 a32] = words-of s
+		[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] = values-of s
+	]
+
 ===end-group===
 
 
@@ -177,6 +186,24 @@ s: make struct! spec: [a: [uint16!] 1 b: [int32!] -1 c: [word!] foo d [uint8! [2
 		error? e: try [ make struct! [a: [int8! [2]] 1] ] ;- No crash!
 		e/id = 'expect-val
 	]
+
+--test-- "Empty struct not allowed"
+	--assert all [
+		error? e: try [make struct! []]
+		e/id = 'invalid-arg
+	]
+	--assert all [
+		error? e: try [make struct! [a]]
+		e/id = 'invalid-arg
+	]
+	--assert all [
+		error? e: try [make struct! [[]]]
+		e/id = 'invalid-arg
+	]
+	--assert all [
+		error? e: try [make struct! [[] a]]
+		e/id = 'invalid-arg
+	]
 ===end-group===