(feat) better diagnostics (#760)

#753, #718

- make it more clear that the JSX-related message is the underlying error to diminish confusion
- add suggestion to ts error

Author: dummdidumm

packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts

@@ -130,13 +130,37 @@ function enhanceIfNecessary(diagnostic: Diagnostic): Diagnostic {
             message:
                 'Type definitions are missing for this Svelte Component. ' +
                 // eslint-disable-next-line max-len
-                'It needs a class definition with at least the property \'$$prop_def\' which should contain a map of input property definitions.\n' +
+                "It needs a class definition with at least the property '$$prop_def' which should contain a map of input property definitions.\n" +
                 'Example:\n' +
-                'class ComponentName { $$prop_def: { propertyName: string; } }\n\n' +
+                '  class ComponentName { $$prop_def: { propertyName: string; } }\n' +
+                'If you are using Svelte 3.31+, use SvelteComponentTyped:\n' +
+                '  import type { SvelteComponentTyped } from "svelte";\n' +
+                '  class ComponentName extends SvelteComponentTyped<{propertyName: string;}> {}\n\n' +
+                'Underlying error:\n' +
                 diagnostic.message
         };
     }
 
+    if (diagnostic.code === 2607) {
+        return {
+            ...diagnostic,
+            message:
+                'Element does not support attributes because ' +
+                'type definitions are missing for this Svelte Component or element cannot be used as such.\n\n' +
+                'Underlying error:\n' +
+                diagnostic.message
+        };
+    }
+
+    if (diagnostic.code === 1184) {
+        return {
+            ...diagnostic,
+            message:
+                diagnostic.message +
+                '\nIf this is a declare statement, move it into <script context="module">..</script>'
+        };
+    }
+
     return diagnostic;
 }