Assert when struct size would exceed 4 GB.

releasenotes.md

@@ -38,6 +38,7 @@
 - Converting between simd/non-simd bool vector would hit a compiler assert. #2691
 - `i<n>` suffixes were not caught when n < 8, causing an assert.
 - Parse error in `$defined` was not handled correctly, leading to an assertion.
+- Assert when struct size would exceed 4 GB.
 
 ### Stdlib changes
 - Add `ThreadPool` join function to wait for all threads to finish in the pool without destroying the threads.

src/compiler/sema_decls.c

@@ -637,7 +637,9 @@ static bool sema_analyse_struct_members(SemaContext *context, Decl *decl)
 
 		offset = align_offset;
 		member->offset = offset;
+		AlignSize sz = offset;
 		offset += type_size(member->type);
+		if (offset < sz || offset > MAX_STRUCT_SIZE) RETURN_SEMA_ERROR(member, "Struct member '%s' would cause the struct to become too large (exceeding 2 GB).", member->name);
 	}
 
 	// Set the alignment:

src/utils/common.h

@@ -29,6 +29,7 @@
 #define DEFAULT_STACK_OBJECT_SIZE 64
 #define MAX_ARRAY_SIZE INT64_MAX
 #define MAX_SOURCE_LOCATION_LEN 255
+#define MAX_STRUCT_SIZE (2U * 1024U * 1024U * 1024U)
 #define PROJECT_JSON "project.json"
 #define PROJECT_JSON5 "project.json5"
 

test/test_suite/struct/struct_too_large.c3

@@ -0,0 +1,12 @@
+import std;
+struct Foo
+{
+    int a;
+    int[int.max] b; // #error: "Struct member 'b' would cause the struct to become too large
+}
+
+fn int main()
+{
+    Foo c = (Foo){};
+    return 0;
+}