From 6eee760239cbd813b5e80980df684a3580840c44 Mon Sep 17 00:00:00 2001
From: Christoffer Lerno <christoffer@aegik.com>
Date: Sat, 11 Oct 2025 16:26:07 +0200
Subject: [PATCH] Add `--max-macro-iterations` to set macro iteration limit.

---
 releasenotes.md                              |  3 ++-
 src/build/build.h                            |  2 ++
 src/build/build_options.c                    | 11 ++++++++++-
 src/build/builder.c                          |  3 ++-
 src/compiler/compiler_internal.h             |  1 -
 src/compiler/sema_stmts.c                    |  7 ++++++-
 src/utils/common.h                           |  2 ++
 test/test_suite/compile_time/ct_for_limit.c3 |  6 ++++++
 8 files changed, 30 insertions(+), 5 deletions(-)
 create mode 100644 test/test_suite/compile_time/ct_for_limit.c3

diff --git a/releasenotes.md b/releasenotes.md
index cb2f4bbe1..1847e46eb 100644
--- a/releasenotes.md
+++ b/releasenotes.md
@@ -9,7 +9,8 @@
 - `"build-dir"` option now available for `project.json`, added to project. #2323
 - Allow `..` ranges to use "a..a-1" in order to express zero length.
 - Disallow aliasing of `@local` symbols with a higher visibility in the alias.
- 
+- Add `--max-macro-iterations` to set macro iteration limit.
+
 ### Fixes
 - Bug in `io::write_using_write_byte`.
 - Bitstruct value cannot be used to index a const array in compile time. #2512
diff --git a/src/build/build.h b/src/build/build.h
index 9db58b8d3..1fdd808f9 100644
--- a/src/build/build.h
+++ b/src/build/build.h
@@ -586,6 +586,7 @@ typedef struct BuildOptions_
 	SanitizeMode sanitize_mode;
 	uint32_t max_vector_size;
 	uint32_t max_stack_object_size;
+	uint32_t max_macro_iterations;
 	bool print_keywords;
 	bool print_attributes;
 	bool print_builtins;
@@ -728,6 +729,7 @@ typedef struct
 	uint32_t symtab_size;
 	uint32_t max_vector_size;
 	uint32_t max_stack_object_size;
+	uint32_t max_macro_iterations;
 	uint32_t switchrange_max_size;
 	uint32_t switchjump_max_size;
 	const char **args;
diff --git a/src/build/build_options.c b/src/build/build_options.c
index 362c9c05e..eee051b94 100644
--- a/src/build/build_options.c
+++ b/src/build/build_options.c
@@ -182,6 +182,7 @@ static void usage(bool full)
 		print_opt("--win-debug=<option>", "Select debug output on Windows: codeview or dwarf (default: codeview).");
 		print_opt("--max-vector-size <number>", "Set the maximum vector bit size to allow (default: 4096).");
 		print_opt("--max-stack-object-size <number>", "Set the maximum size of a stack object in KB (default: 128).");
+		print_opt("--max-macro-iterations <number>", "Set the maximum number of iterations in a macro loop (default: 1048575).");
 		PRINTF("");
 		print_opt("--print-linking", "Print linker arguments.");
 		PRINTF("");
@@ -972,10 +973,18 @@ static void parse_option(BuildOptions *options)
 			{
 				int size = (at_end() || next_is_opt()) ? 0 : atoi(next_arg());
 				if (size < 1) error_exit("Expected a valid positive integer >= 1 for --max-stack-object-size.");
-				if (size > MAX_STACK_OBJECT_SIZE) error_exit("Expected a valid positive integer <= %u for --max-vector-size.", (unsigned)MAX_STACK_OBJECT_SIZE);
+				if (size > MAX_STACK_OBJECT_SIZE) error_exit("Expected a valid positive integer <= %u for --max-stack-object-size.", (unsigned)MAX_STACK_OBJECT_SIZE);
 				options->max_stack_object_size = size;
 				return;
 			}
+			if (match_longopt("max-macro-iterations"))
+			{
+				int size = (at_end() || next_is_opt()) ? 0 : atoi(next_arg());
+				if (size < 1) error_exit("Expected a valid positive integer >= 128 for --max-macro-iterations");
+				if (size > MAX_MACRO_ITERATIONS) error_exit("Expected a valid positive integer <= %u for --max-macro-iterations.", (unsigned)MAX_MACRO_ITERATIONS);
+				options->max_macro_iterations = size;
+				return;
+			}
 			if (match_longopt("max-vector-size"))
 			{
 				int size = (at_end() || next_is_opt()) ? 0 : atoi(next_arg());
diff --git a/src/build/builder.c b/src/build/builder.c
index 5f6e0d047..2ec77017e 100644
--- a/src/build/builder.c
+++ b/src/build/builder.c
@@ -432,6 +432,7 @@ static void update_build_target_from_options(BuildTarget *target, BuildOptions *
 	OVERRIDE_IF_SET(symtab_size);
 	OVERRIDE_IF_SET(max_vector_size);
 	OVERRIDE_IF_SET(max_stack_object_size);
+	OVERRIDE_IF_SET(max_macro_iterations);
 	OVERRIDE_IF_SET(win.def);
 	OVERRIDE_IF_SET(no_entry);
 	OVERRIDE_IF_SET(echo_prefix);
@@ -448,7 +449,7 @@ static void update_build_target_from_options(BuildTarget *target, BuildOptions *
 
 	if (!target->max_vector_size) target->max_vector_size = DEFAULT_VECTOR_WIDTH;
 	if (!target->max_stack_object_size) target->max_stack_object_size = DEFAULT_STACK_OBJECT_SIZE;
-
+	if (!target->max_macro_iterations) target->max_macro_iterations = DEFAULT_MAX_MACRO_ITERATIONS;
 	if (target->quiet && !options->verbosity_level) options->verbosity_level = -1;
 
 	if (options->silence_deprecation || options->verbosity_level < 0) target->silence_deprecation = true;
diff --git a/src/compiler/compiler_internal.h b/src/compiler/compiler_internal.h
index a540ad838..a7c55c421 100644
--- a/src/compiler/compiler_internal.h
+++ b/src/compiler/compiler_internal.h
@@ -42,7 +42,6 @@ typedef uint16_t FileId;
 #define INITIAL_SYMBOL_MAP 0x10000
 #define INITIAL_GENERIC_SYMBOL_MAP 0x1000
 #define MAX_INCLUDE_DIRECTIVES 2048
-#define MAX_MACRO_ITERATIONS 0xFFFFFF
 #define MAX_PARAMS 255
 #define MAX_BITSTRUCT 0x1000
 #define MAX_MEMBERS ((StructIndex)1) << 15
diff --git a/src/compiler/sema_stmts.c b/src/compiler/sema_stmts.c
index 8c773d1c6..d39a008d4 100644
--- a/src/compiler/sema_stmts.c
+++ b/src/compiler/sema_stmts.c
@@ -3110,8 +3110,13 @@ static inline bool sema_analyse_ct_for_stmt(SemaContext *context, Ast *statement
 	// We set a maximum of macro iterations.
 	// we might consider reducing this.
 	unsigned current_ct_scope = sema_context_push_ct_stack(context);
-	for (int i = 0; i < MAX_MACRO_ITERATIONS; i++)
+	for (int i = 0; ; i++)
 	{
+		if (i >= compiler.build.max_macro_iterations)
+		{
+			SEMA_ERROR(statement, "Too many iterations in '$for' (it exceeded %d), you can change this limit using '--max-macro-iterations'.", compiler.build.max_macro_iterations);
+			goto FAILED;
+		}
 		sema_context_pop_ct_stack(context, current_ct_scope);
 		// First evaluate the cond, which we note that we *must* have.
 		// we need to make a copy
diff --git a/src/utils/common.h b/src/utils/common.h
index 98b1ae57b..4a5d59e69 100644
--- a/src/utils/common.h
+++ b/src/utils/common.h
@@ -23,6 +23,8 @@
 #define NO_ARENA 0
 #define MAX_VECTOR_WIDTH 65536
 #define MAX_STACK_OBJECT_SIZE (256 * 1024)
+#define MAX_MACRO_ITERATIONS 0xFFFFFF
+#define DEFAULT_MAX_MACRO_ITERATIONS 0xFFFFF
 #define DEFAULT_VECTOR_WIDTH 4096
 #define DEFAULT_STACK_OBJECT_SIZE 64
 #define MAX_ARRAY_SIZE INT64_MAX
diff --git a/test/test_suite/compile_time/ct_for_limit.c3 b/test/test_suite/compile_time/ct_for_limit.c3
new file mode 100644
index 000000000..50222bc9b
--- /dev/null
+++ b/test/test_suite/compile_time/ct_for_limit.c3
@@ -0,0 +1,6 @@
+fn int main()
+{
+	$for var $i = 0; $i < 1000000000; $i++: // #error: Too many iterations in
+	$endfor
+	return 0;
+}
\ No newline at end of file