A file with an inferred module may not contain additional other modules.

releasenotes.md

@@ -26,6 +26,7 @@
 - `@assignable_to` is deprecated in favour of `$define`
 - Add `linklib-dir` to c3l-libraries to place their linked libraries in. Defaults to `linked-libs`
 - If the `os-arch` linked library doesn't exist, try with `os` for c3l libs.
+- A file with an inferred module may not contain additional other modules.
 
 ### Fixes
 - List.remove_at would incorrectly trigger ASAN.

src/compiler/compiler_internal.h

@@ -1698,6 +1698,7 @@ struct CompilationUnit_
 	bool is_interface_file;
 	bool benchmark_by_default;
 	bool test_by_default;
+	bool module_generated;
 	Attr **attr_links;
 	Decl **generic_defines;
 	Decl **ct_asserts;

src/compiler/context.c

@@ -121,7 +121,7 @@ bool context_set_module_from_filename(ParseContext *context)
 		return false;
 	}
 	Path *path = CALLOCS(Path);
-	path->span = INVALID_SPAN;
+	path->span = context->span;
 	path->module = module_name;
 	path->len = scratch_buffer.len;
 	return create_module_or_check_name(context->unit, path, NULL);

src/compiler/parse_global.c

@@ -3190,6 +3190,7 @@ Decl *parse_top_level_statement(ParseContext *c, ParseContext **context_out)
 	if (tok != TOKEN_MODULE && !c->unit->module)
 	{
 		if (!context_set_module_from_filename(c)) return poisoned_decl;
+		c->unit->module_generated = true;
 		// Pass the docs to the next thing.
 	}
 
@@ -3230,6 +3231,14 @@ Decl *parse_top_level_statement(ParseContext *c, ParseContext **context_out)
 			advance(c);
 			if (c->unit->module)
 			{
+				if (c->unit->module_generated)
+				{
+					print_error_at(c->unit->module->name->span, "This file begins with an auto-generated module '%s', which isn't compatible with having other module sections, please start the file with an explicit 'module'.",
+						c->unit->module->name->module);
+					sema_note_prev_at(c->span, "This declaration creates the next module section.");
+					c->unit->module_generated = false;
+					return poisoned_decl;
+				}
 				// We might run into another module declaration. If so, create a new unit.
 				ParseContext *new_context = CALLOCS(ParseContext);
 				*new_context = *c;

test/test_suite/attributes/format_macros.c3t

@@ -1,5 +1,3 @@
-import std;
-
 module abort_test;
 
 fn int main()

test/test_suite/methods/method_lookup_extensions_2208.c3

@@ -1,3 +1,4 @@
+module okok;
 fn void main() {}
 module foo @private;