Fix panic when parsing wrong import statement

Have to be several tests because the parser bails out at the first error.
The error message is not optimal but better than a panic

sixtyfps_compiler/tests/syntax/imports/import_parse_error1.60

@@ -0,0 +1,13 @@
+ /* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+
+import;
+//    ^error{Syntax error: expected LBrace}
+

sixtyfps_compiler/tests/syntax/imports/import_parse_error2.60

@@ -0,0 +1,13 @@
+ /* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+
+import foo from bar;
+//     ^error{Syntax error: expected LBrace}
+

sixtyfps_compiler/tests/syntax/imports/import_parse_error3.60

@@ -0,0 +1,13 @@
+ /* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+
+import { A } yo;
+//           ^error{Expected from keyword for import statement}
+

sixtyfps_compiler/tests/syntax/imports/import_parse_error4.60

@@ -0,0 +1,13 @@
+ /* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+
+import { } from yo;
+//              ^error{Expected plain string literal}
+

sixtyfps_compiler/typeloader.rs

@@ -297,10 +297,15 @@ impl<'a> TypeLoader<'a> {
             // If there was error (esp parse error) we don't want to report further error in this document.
             // because they might be nonsense (TODO: we should check that the parse error were really in this document).
             // But we still want to create a document to give better error messages in the root document.
+            let mut ignore_diag = BuildDiagnostics::default();
+            ignore_diag.push_error_with_span(
+                "Dummy error because some of the code asserts there there was an error".into(),
+                Default::default(),
+            );
             let doc = crate::object_tree::Document::from_node(
                 dependency_doc,
                 foreign_imports,
-                &mut BuildDiagnostics::default(), // New diagnostics that we will ignore
+                &mut ignore_diag,
                 &dependency_registry,
             );
             self.all_documents.docs.insert(path.to_owned(), doc);
@@ -406,9 +411,13 @@ impl<'a> TypeLoader<'a> {
         let mut dependencies = DependenciesByFile::new();
 
         for import in doc.ImportSpecifier() {
-            let import_uri = import.child_token(SyntaxKind::StringLiteral).expect(
+            let import_uri = match import.child_token(SyntaxKind::StringLiteral) {
-                "Internal error: missing import uri literal, this is a parsing/grammar bug",
+                Some(import_uri) => import_uri,
-            );
+                None => {
+                    debug_assert!(doc_diagnostics.has_error());
+                    continue;
+                }
+            };
             let path_to_import = import_uri.text().to_string();
             let path_to_import = path_to_import.trim_matches('\"').to_string();
             if path_to_import.is_empty() {