fix: incorrect name in prod diagnostic

Author: posva

docs/content/4.api/1.reference.md

@@ -67,7 +67,7 @@ interface DiagnosticCallParams {
 
 ### `defineProdDiagnostics(options?)`
 
-Lean production counterpart to `defineDiagnostics`. Returns a `Proxy` that builds a minimal `Diagnostic` for any accessed code: the code becomes the `message` (`why`), `name` stays the default `Diagnostic`, and `docs` is derived from `docsBase`. It carries no catalog text, so it stays tiny in a bundle.
+Lean production counterpart to `defineDiagnostics`. Returns a `Proxy` that builds a minimal `Diagnostic` for any accessed code: the code becomes both the `message` (`why`) and the instance `name`, and `docs` is derived from `docsBase`. It carries no catalog text, so it stays tiny in a bundle.
 
 ```ts
 const diagnostics = defineProdDiagnostics({

src/prod-diagnostics.test.ts

@@ -10,10 +10,11 @@ describe('defineProdDiagnostics', () => {
     expect(d).toBeInstanceOf(Diagnostic)
   })
 
-  it('uses the accessed code as `why` and keeps the default `name`', () => {
+  it('uses the accessed code as `why` and as the instance `name`', () => {
     const errs = defineProdDiagnostics()
     const d = errs.NUXT_B2011()
-    expect(d.name).toBe('Diagnostic')
+    // parity with defineDiagnostics: the code becomes the instance name
+    expect(d.name).toBe('NUXT_B2011')
     expect(d.message).toBe('NUXT_B2011')
     expect(d.why).toBe('NUXT_B2011')
   })

src/prod-diagnostics.ts

@@ -32,9 +32,8 @@ export interface DefineProdDiagnosticsOptions<
 /**
  * Production counterpart to {@link defineDiagnostics}. Returns a `Proxy` that
  * builds a minimal {@link Diagnostic} for any accessed code: the code becomes
- * the `message` (`why`), `name` stays the default `'Diagnostic'`, and `docs` is
- * derived from `docsBase`. It carries no catalog text, so it stays tiny in a
- * bundle.
+ * both the `message` (`why`) and the instance `name`, and `docs` is derived
+ * from `docsBase`. It carries no catalog text, so it stays tiny in a bundle.
  *
  * The strip plugin (`@nostics/unplugin`) can rewrite a `defineDiagnostics()`
  * call into a `process.env.NODE_ENV === 'production'` ternary that selects this
@@ -72,6 +71,7 @@ export function defineProdDiagnostics<
           },
           handle,
         )
+        diagnostic.name = code
         for (const reporter of reporters) reporter(diagnostic, reporterOptions)
         return diagnostic
       }