- Better error messages when slicing a pointer to a slice or vector. #2681

releasenotes.md

@@ -10,6 +10,7 @@
 - Support for NetBSD.
 - Testing for the presence of methods at the top level is prohibited previous to method registration.
 - `$$MASK_TO_INT` and `$$INT_TO_MASK` to create bool masks from integers and back.
+- Better error messages when slicing a pointer to a slice or vector. #2681
 
 ### Fixes
 - Regression with npot vector in struct triggering an assert #2219.

src/compiler/sema_expr.c

@@ -4450,7 +4450,7 @@ typedef enum RangeEnv
 	RANGE_FLEXIBLE,
 } RangeEnv;
 
-INLINE bool sema_expr_analyse_range_internal(SemaContext *context, Range *range, ArrayIndex len, RangeEnv env)
+INLINE bool sema_expr_analyse_range_internal(SemaContext *context, Range *range, ArrayIndex len, RangeEnv env, FlatType *indexed_type)
 {
 	Expr *start = exprptr(range->start);
 	ASSERT(start);
@@ -4482,14 +4482,26 @@ INLINE bool sema_expr_analyse_range_internal(SemaContext *context, Range *range,
 	{
 		if (range->start_from_end)
 		{
+			if (indexed_type->type_kind == TYPE_POINTER && type_is_any_arraylike(indexed_type->pointer))
+			{
+				RETURN_SEMA_ERROR(start, "Indexing from the end is not allowed for pointers, did you perhaps forget to dereference the pointer before []?");
+			}
 			RETURN_SEMA_ERROR(start, "Indexing from the end is not allowed for pointers or flexible array members.");
 		}
 		if (!end)
 		{
+			if (indexed_type->type_kind == TYPE_POINTER && type_is_any_arraylike(indexed_type->pointer))
+			{
+				RETURN_SEMA_ERROR(start, "Omitting the end index is not allowed for pointers, did you perhaps forget to dereference the pointer before slicing wih []?");
+			}
 			RETURN_SEMA_ERROR(start, "Omitting end index is not allowed for pointers or flexible array members.");
 		}
 		if (end && range->end_from_end)
 		{
+			if (indexed_type->type_kind == TYPE_POINTER && type_is_any_arraylike(indexed_type->pointer))
+			{
+				RETURN_SEMA_ERROR(start, "Indexing from the end is not allowed for pointers, did you perhaps forget to dereference the pointer before []?");
+			}
 			RETURN_SEMA_ERROR(end, "Indexing from the end is not allowed for pointers or flexible array members.");
 		}
 	}
@@ -4609,7 +4621,7 @@ INLINE bool sema_expr_analyse_range_internal(SemaContext *context, Range *range,
 }
 
 
-static inline bool sema_expr_analyse_range(SemaContext *context, Range *range, ArrayIndex len, RangeEnv env)
+static inline bool sema_expr_analyse_range(SemaContext *context, Range *range, ArrayIndex len, RangeEnv env, FlatType *indexed_type)
 {
 	switch (range->status)
 	{
@@ -4617,7 +4629,7 @@ static inline bool sema_expr_analyse_range(SemaContext *context, Range *range, A
 			return true;
 		case RESOLVE_NOT_DONE:
 			range->status = RESOLVE_RUNNING;
-			if (!sema_expr_analyse_range_internal(context, range, len, env))
+			if (!sema_expr_analyse_range_internal(context, range, len, env, indexed_type))
 			{
 				range->status = RESOLVE_NOT_DONE;
 				return false;
@@ -4733,7 +4745,7 @@ static inline bool sema_expr_analyse_slice(SemaContext *context, Expr *expr)
 	}
 	ArrayIndex length = sema_len_from_expr(subscripted);
 	Range *range = &expr->slice_expr.range;
-	if (!sema_expr_analyse_range(context, range, length, env)) return false;
+	if (!sema_expr_analyse_range(context, range, length, env, type)) return false;
 	if (range->is_optional) optional = true;
 	if (sema_cast_const(subscripted) && range->range_type == RANGE_CONST_RANGE)
 	{

test/test_suite/slices/slice_error_improvement.c3

@@ -0,0 +1,34 @@
+import std;
+
+
+macro transpose4x4_mat(a, b, c, d)
+{
+    Matrix4x4{float} mat;
+
+    mat.m[0..3] = *a[..]; // #error: Omitting the end index is not allowed for pointers, did you perhaps forget to dereference the pointer before slicing wih []?
+    mat.m[4..7] = *b[..];
+    mat.m[8..11] = *c[..];
+    mat.m[12..15] = *d[..];
+
+    mat = mat.transpose();
+
+    *a = mat.m[0..3];
+    *b = mat.m[4..7];
+    *c = mat.m[8..11];
+    *d = mat.m[12..15];
+}
+
+fn void main()
+{
+    float[<4>] a = { 0,1,2,3 };
+    float[<4>] b = { 4,5,6,7 };
+    float[<4>] c = { 8,9,10,11 };
+    float[<4>] d = { 12,13,14,15 };
+
+    transpose4x4_mat(&a, &b, &c, &d);
+
+    io::printn(a);
+    io::printn(b);
+    io::printn(c);
+    io::printn(d);
+}