Generalize Odin call-based "iterators" to work with more than 2-values: `for x, y, z, w in iterate(&it)`

It has an artificial limitation of 100 values because if you need for than that, you're doing something wrong.

src/check_stmt.cpp

@@ -1669,12 +1669,20 @@ gb_internal void check_range_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags)
 			case Type_Tuple:
 				{
 					isize count = t->Tuple.variables.count;
-					if (count < 1 || count > 3) {
+					if (count < 1) {
 						ERROR_BLOCK();
 						check_not_tuple(ctx, &operand);
-						error_line("\tMultiple return valued parameters in a range statement are limited to a maximum of 2 usable values with a trailing boolean for the conditional\n");
+						error_line("\tMultiple return valued parameters in a range statement are limited to a minimum of 1 usable values with a trailing boolean for the conditional, got %td\n", count);
 						break;
 					}
+					enum : isize {MAXIMUM_COUNT = 100};
+					if (count > MAXIMUM_COUNT) {
+						ERROR_BLOCK();
+						check_not_tuple(ctx, &operand);
+						error_line("\tMultiple return valued parameters in a range statement are limited to a maximum of %td usable values with a trailing boolean for the conditional, got %td\n", MAXIMUM_COUNT, count);
+						break;
+					}
+
 					Type *cond_type = t->Tuple.variables[count-1]->type;
 					if (!is_type_boolean(cond_type)) {
 						gbString s = type_to_string(cond_type);
@@ -1683,24 +1691,23 @@ gb_internal void check_range_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags)
 						break;
 					}
 
+					max_val_count = count;
+
 					for (Entity *e : t->Tuple.variables) {
 						array_add(&vals, e->type);
 					}
 
 					is_possibly_addressable = false;
 
-					if (rs->vals.count > 1 && rs->vals[1] != nullptr && count < 3) {
-						gbString s = type_to_string(t);
-						error(operand.expr, "Expected a 3-valued expression on the rhs, got (%s)", s);
-						gb_string_free(s);
-						break;
-					}
-
-					if (rs->vals.count > 0 && rs->vals[0] != nullptr && count < 2) {
-						gbString s = type_to_string(t);
-						error(operand.expr, "Expected at least a 2-valued expression on the rhs, got (%s)", s);
-						gb_string_free(s);
-						break;
+					bool do_break = false;
+					for (isize i = rs->vals.count-1; i >= 0; i--) {
+						if (rs->vals[i] != nullptr && count < i+2) {
+							gbString s = type_to_string(t);
+							error(operand.expr, "Expected a %td-valued expression on the rhs, got (%s)", i+2, s);
+							gb_string_free(s);
+							do_break = true;
+							break;
+						}
 					}
 
 					if (is_reverse) {

src/llvm_backend_stmt.cpp

@@ -802,8 +802,19 @@ gb_internal void lb_build_range_enum(lbProcedure *p, Type *enum_type, Type *val_
 	if (done_) *done_ = done;
 }
 
-gb_internal void lb_build_range_tuple(lbProcedure *p, Ast *expr, Type *val0_type, Type *val1_type,
-                                      lbValue *val0_, lbValue *val1_, lbBlock **loop_, lbBlock **done_) {
+gb_internal void lb_build_range_tuple(lbProcedure *p, AstRangeStmt *rs, Scope *scope) {
+	Ast *expr = unparen_expr(rs->expr);
+
+	Type *expr_type = type_of_expr(expr);
+	Type *et = base_type(type_deref(expr_type));
+	GB_ASSERT(et->kind == Type_Tuple);
+
+	i32 value_count = cast(i32)et->Tuple.variables.count;
+
+	lbValue *values = gb_alloc_array(permanent_allocator(), lbValue, value_count);
+
+	lb_open_scope(p, scope);
+
 	lbBlock *loop = lb_create_block(p, "for.tuple.loop");
 	lb_emit_jump(p, loop);
 	lb_start_block(p, loop);
@@ -821,11 +832,26 @@ gb_internal void lb_build_range_tuple(lbProcedure *p, Ast *expr, Type *val0_type
 	lb_emit_if(p, cond, body, done);
 	lb_start_block(p, body);
 
+	for (i32 i = 0; i < value_count; i++) {
+		values[i] = lb_emit_tuple_ev(p, tuple_value, i);
+	}
 
-	if (val0_) *val0_ = lb_emit_tuple_ev(p, tuple_value, 0);
-	if (val1_) *val1_ = lb_emit_tuple_ev(p, tuple_value, 1);
-	if (loop_) *loop_ = loop;
-	if (done_) *done_ = done;
+	GB_ASSERT(rs->vals.count <= value_count);
+	for (isize i = 0; i < rs->vals.count; i++) {
+		Ast *val = rs->vals[i];
+		if (val != nullptr) {
+			lb_store_range_stmt_val(p, val, values[i]);
+		}
+	}
+
+	lb_push_target_list(p, rs->label, done, loop, nullptr);
+
+	lb_build_stmt(p, rs->body);
+
+	lb_close_scope(p, lbDeferExit_Default, nullptr);
+	lb_pop_target_list(p);
+	lb_emit_jump(p, loop);
+	lb_start_block(p, done);
 }
 
 gb_internal void lb_build_range_stmt_struct_soa(lbProcedure *p, AstRangeStmt *rs, Scope *scope) {
@@ -968,6 +994,17 @@ gb_internal void lb_build_range_stmt(lbProcedure *p, AstRangeStmt *rs, Scope *sc
 		}
 	}
 
+	TypeAndValue tav = type_and_value_of_expr(expr);
+	if (tav.mode != Addressing_Type) {
+		Type *expr_type = type_of_expr(expr);
+		Type *et = base_type(type_deref(expr_type));
+		if (et->kind == Type_Tuple) {
+			lb_build_range_tuple(p, rs, scope);
+			return;
+		}
+	}
+
+
 	lb_open_scope(p, scope);
 
 	Ast *val0 = rs->vals.count > 0 ? lb_strip_and_prefix(rs->vals[0]) : nullptr;
@@ -986,7 +1023,6 @@ gb_internal void lb_build_range_stmt(lbProcedure *p, AstRangeStmt *rs, Scope *sc
 	lbBlock *loop = nullptr;
 	lbBlock *done = nullptr;
 	bool is_map = false;
-	TypeAndValue tav = type_and_value_of_expr(expr);
 
 	if (tav.mode == Addressing_Type) {
 		lb_build_range_enum(p, type_deref(tav.type), val0_type, &val, &key, &loop, &done);
@@ -1062,8 +1098,7 @@ gb_internal void lb_build_range_stmt(lbProcedure *p, AstRangeStmt *rs, Scope *sc
 			break;
 		}
 		case Type_Tuple:
-			lb_build_range_tuple(p, expr, val0_type, val1_type, &val, &key, &loop, &done);
-			break;
+			GB_PANIC("Should be handled already");
 
 		case Type_BitSet: {
 			lbModule *m = p->module;