handle import same file twice (#414)

self_hosted/main.jou

@@ -227,6 +227,8 @@ class Compiler:
 
         for idest = 0; idest < self->nfiles; idest++:
             dest = &self->files[idest]
+            seen_before: FileState** = malloc(sizeof(seen_before[0]) * dest->ast.nimports)
+
             for i = 0; i < dest->ast.nimports; i++:
                 imp = &dest->ast.imports[i]
 
@@ -235,10 +237,17 @@ class Compiler:
                     if strcmp(self->files[isrc].ast.path, imp->resolved_path) == 0:
                         src = &self->files[isrc]
                         break
+                assert src != NULL
+
                 if src == dest:
                     fail(imp->location, "the file itself cannot be imported")
 
-                assert src != NULL
+                for k = 0; k < i; k++:
+                    if seen_before[k] == src:
+                        message: byte[500]
+                        snprintf(message, sizeof(message), "file \"%s\" is imported twice", imp->specified_path)
+                        fail(imp->location, message)
+                seen_before[i] = src
 
                 for exp = src->pending_exports; exp->name[0] != '\0'; exp++:
                     if self->verbosity >= 1:
@@ -249,6 +258,8 @@ class Compiler:
                     check_ast_and_import_conflicts(&dest->ast, exp)
                     dest->typectx.add_imported_symbol(exp)
 
+            free(seen_before)
+
         for i = 0; i < self->nfiles; i++:
             free(self->files[i].pending_exports)
             self->files[i].pending_exports = NULL

src/main.c

@@ -370,13 +370,22 @@ static void add_imported_symbol(struct FileState *fs, const ExportSymbol *es, As
 static void add_imported_symbols(struct CompileState *compst)
 {
     for (struct FileState *to = compst->files.ptr; to < End(compst->files); to++) {
+        List(struct FileState *) seen_before = {0};
+
         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 (int i = 0; i < seen_before.len; i++) {
+                if (seen_before.ptr[i] == from) {
+                    fail_with_error(imp->location, "file \"%s\" is imported twice", imp->specified_path);
+                }
+            }
+            Append(&seen_before, from);
+
             for (struct ExportSymbol *es = from->pending_exports; es->name[0]; es++) {
                 if (command_line_args.verbosity >= 2) {
                     const char *kindstr;
@@ -391,6 +400,8 @@ static void add_imported_symbols(struct CompileState *compst)
                 add_imported_symbol(to, es, imp);
             }
         }
+
+        free(seen_before.ptr);
     }
 
     // Mark all exports as no longer pending.

tests/other_errors/double_import.jou

@@ -0,0 +1,2 @@
+import "stdlib/io.jou"
+import "stdlib/io.jou"  # Error: file "stdlib/io.jou" is imported twice