Fix TODO: the file itself cannot be imported (#393)

Co-authored-by: Akuli <[email protected]>

self_hosted/main.jou

@@ -235,6 +235,9 @@ class Compiler:
                     if strcmp(self->files[isrc].ast.path, imp->resolved_path) == 0:
                         src = &self->files[isrc]
                         break
+                if src == dest:
+                    fail(imp->location, "the file itself cannot be imported")
+
                 assert src != NULL
 
                 for exp = src->pending_exports; exp->name[0] != '\0'; exp++:

src/main.c

@@ -365,12 +365,13 @@ static void add_imported_symbol(struct FileState *fs, const ExportSymbol *es, As
 
 static void add_imported_symbols(struct CompileState *compst)
 {
-    // TODO: should it be possible for a file to import from itself?
-    // Should fail with error?
     for (struct FileState *to = compst->files.ptr; to < End(compst->files); to++) {
         for (AstImport *imp = to->ast.imports.ptr; imp < End(to->ast.imports); imp++) {
             struct FileState *from = find_file(compst, imp->resolved_path);
             assert(from);
+            if (from == to) {
+                fail_with_error(imp->location, "the file itself cannot be imported");
+            }
 
             for (struct ExportSymbol *es = from->pending_exports; es->name[0]; es++) {
                 if (command_line_args.verbosity >= 2) {

tests/other_errors/import_it_self.jou

@@ -0,0 +1,4 @@
+import "./import_it_self.jou" # Error: the file itself cannot be imported
+
+def main() -> int:
+    return 0