Chart builder: drop unparseable expressions mid-edit, polite glyphed inline feedback

src/core/chart-builder.ts

@@ -26,6 +26,7 @@ import type { ColumnStats } from './profile';
 import { DISTINCT_CAP } from './profile';
 import type { ColumnType } from './type-inference';
 import { VEGA_LITE_SCHEMA_URL } from './snippet';
+import { validateExpression } from './expr-validate';
 
 /** The five mark types the builder offers, in selector order (spec §06). */
 export const MARK_TYPES = ['bar', 'line', 'point', 'area', 'circle'] as const;
@@ -835,25 +836,31 @@ function predicateObject(filter: BuilderFilter): Record<string, unknown> | null
 function filterTransformObject(filter: BuilderFilter): Record<string, unknown> | null {
   if (filter.mode === 'expression') {
     const expr = (filter.expr ?? '').trim();
-    return expr === '' ? null : { filter: expr };
+    // A syntactically-invalid expression is dropped like an empty one: a half-typed
+    // `datum.x *` must not reach the renderer and blank the preview mid-edit — the
+    // inline feedback already flags it. (Same mid-edit resilience as a partial predicate.)
+    return expr === '' || !validateExpression(expr).valid ? null : { filter: expr };
   }
   const predicate = predicateObject(filter);
   return predicate ? { filter: predicate } : null;
 }
 
-/** One calculate's `{ calculate, as }` transform entry, or `null` when incomplete. */
+/** One calculate's `{ calculate, as }` transform entry, or `null` when incomplete or unparseable. */
 function calculateTransformObject(calc: BuilderCalculate): Record<string, unknown> | null {
   const expr = calc.expr.trim();
   const as = calc.as.trim();
-  return expr === '' || as === '' ? null : { calculate: expr, as };
+  return expr === '' || as === '' || !validateExpression(expr).valid
+    ? null
+    : { calculate: expr, as };
 }
 
 /**
  * The complete top-level `transform` array for a configuration: every calculated
  * field first (so filters and encodings can reference the derived columns), then
- * every filter, each in the user's list order. Incomplete entries (a half-typed
- * filter, an unnamed calculate) are dropped so a configuration mid-edit still
- * produces a renderable spec. An empty result means no `transform` key is emitted.
+ * every filter, each in the user's list order. Incomplete or unparseable entries (a
+ * half-typed predicate, an unnamed calculate, an expression that doesn't parse) are
+ * dropped so a configuration mid-edit still produces a renderable spec. An empty
+ * result means no `transform` key is emitted.
  */
 export function buildTransforms(config: BuilderConfig): Array<Record<string, unknown>> {
   const out: Array<Record<string, unknown>> = [];