refactor(ui): make diff row dispatch exhaustive

.changeset/brave-rows-narrow.md

@@ -0,0 +1,2 @@
+---
+---

packages/hunk/src/ui/diff/CodeRowView.test.tsx

@@ -3,7 +3,8 @@ import { testRender } from "@opentui/react/test-utils";
 import { act } from "react";
 import { capturedTestColorToHex } from "../../../../../test/helpers/test-color-helpers";
 import { resolveTheme } from "../themes";
-import { CodeRowView, type PlannedCodeReviewRow } from "./CodeRowView";
+import { CodeRowView } from "./CodeRowView";
+import type { PlannedCodeReviewRow } from "./reviewRenderPlan";
 import { cursorLineHighlightBg, selectionHighlightBg, stackCellPalette } from "./rowStyle";
 
 /** Return the normalized background painted behind matching captured text. */

packages/hunk/src/ui/diff/CodeRowView.tsx

@@ -3,15 +3,11 @@ import type { UserNoteLineTarget } from "../../core/liveComments";
 import type { CopySelectedRowRange } from "../lib/diffSpatial";
 import type { AppTheme } from "../themes";
 import { CODE_ROW_ADD_NOTE_BADGE_TEXT, CODE_ROW_ADD_NOTE_BADGE_WIDTH } from "./codeRowAffordance";
-import {
-  planCodeRowLayout,
-  type CodeRowLayoutPlan,
-  type PlannedDiffReviewRow,
-} from "./codeRowLayout";
+import { planCodeRowLayout, type CodeRowLayoutPlan } from "./codeRowLayout";
 import { codeCellView, FULL_CODE_CELL_COL_RANGE, type CodeCellHighlight } from "./CodeCellView";
 import type { CursorHighlight } from "./cursorHighlight";
-import type { DiffRow } from "./diffRows";
 import type { LineHighlightPaintIndex } from "./lineHighlightPaint";
+import type { CodeDiffRow, PlannedCodeReviewRow } from "./reviewRenderPlan";
 import {
   cursorLineHighlightBg,
   diffRailMarker,
@@ -22,13 +18,6 @@ import {
 } from "./rowStyle";
 import { markNestedRowMouseAction } from "./rowMouseActions";
 
-type CodeDiffRow = Extract<DiffRow, { type: "split-line" | "stack-line" }>;
-
-/** Planned review row carrying split or stack code cells. */
-export type PlannedCodeReviewRow = Omit<PlannedDiffReviewRow, "row"> & {
-  row: CodeDiffRow;
-};
-
 export interface CodeRowViewProps {
   plannedRow: PlannedCodeReviewRow;
   width: number;

packages/hunk/src/ui/diff/DiffMetaRowView.tsx

@@ -3,19 +3,11 @@ import type { UserNoteLineTarget } from "../../core/liveComments";
 import { reviewGapId } from "../../core/review/expansion";
 import type { AppTheme } from "../themes";
 import { CODE_ROW_ADD_NOTE_BADGE_TEXT } from "./codeRowAffordance";
-import type { PlannedDiffReviewRow } from "./codeRowLayout";
-import type { DiffRow } from "./diffRows";
+import type { PlannedDiffMetaReviewRow } from "./reviewRenderPlan";
 import { fitText } from "./plannedRowText";
 import { diffRailMarker, dimRailColor, neutralRailColor } from "./rowStyle";
 import { markNestedRowMouseAction } from "./rowMouseActions";
 
-type DiffMetaRow = Extract<DiffRow, { type: "collapsed" | "hunk-header" }>;
-
-/** Planned review row carrying metadata rather than code cells. */
-export type PlannedDiffMetaReviewRow = Omit<PlannedDiffReviewRow, "row"> & {
-  row: DiffMetaRow;
-};
-
 export interface DiffMetaRowViewProps {
   plannedRow: PlannedDiffMetaReviewRow;
   width: number;

packages/hunk/src/ui/diff/DiffRowView.tsx

@@ -3,11 +3,15 @@ import { memo } from "react";
 import type { UserNoteLineTarget } from "../../core/liveComments";
 import type { CopySelectedRowRange } from "../lib/diffSpatial";
 import type { AppTheme } from "../themes";
-import { CodeRowView, type PlannedCodeReviewRow } from "./CodeRowView";
-import type { PlannedDiffReviewRow } from "./codeRowLayout";
+import { CodeRowView } from "./CodeRowView";
 import type { CursorHighlight } from "./cursorHighlight";
-import { DiffMetaRowView, type PlannedDiffMetaReviewRow } from "./DiffMetaRowView";
+import { DiffMetaRowView } from "./DiffMetaRowView";
 import type { LineHighlightPaintIndex } from "./lineHighlightPaint";
+import {
+  isPlannedCodeReviewRow,
+  isPlannedDiffMetaReviewRow,
+  type PlannedDiffReviewRow,
+} from "./reviewRenderPlan";
 
 /** Inputs accepted by the memoized diff-row facade. */
 export interface DiffRowViewProps {
@@ -32,6 +36,11 @@ export interface DiffRowViewProps {
   onToggleGap?: (gapKey: string) => void;
 }
 
+/** Reject a planned row variant that lacks a mounted row view. */
+function unsupportedPlannedDiffRow(plannedRow: never): never {
+  throw new Error(`Unsupported planned diff row: ${JSON.stringify(plannedRow)}`);
+}
+
 /**
  * Render one diff row, memoized to avoid unnecessary rerenders.
  *
@@ -58,10 +67,10 @@ export const DiffRowView = memo(function DiffRowViewComponent({
   onStartUserNoteAtHunk,
   onToggleGap,
 }: DiffRowViewProps) {
-  if (plannedRow.row.type === "collapsed" || plannedRow.row.type === "hunk-header") {
+  if (isPlannedDiffMetaReviewRow(plannedRow)) {
     return (
       <DiffMetaRowView
-        plannedRow={plannedRow as PlannedDiffMetaReviewRow}
+        plannedRow={plannedRow}
         width={width}
         theme={theme}
         selected={selected || copySelectedRowRange !== undefined}
@@ -74,10 +83,10 @@ export const DiffRowView = memo(function DiffRowViewComponent({
     );
   }
 
-  if (plannedRow.row.type === "split-line" || plannedRow.row.type === "stack-line") {
+  if (isPlannedCodeReviewRow(plannedRow)) {
     return (
       <CodeRowView
-        plannedRow={plannedRow as PlannedCodeReviewRow}
+        plannedRow={plannedRow}
         width={width}
         lineNumberDigits={lineNumberDigits}
         showLineNumbers={showLineNumbers}
@@ -96,9 +105,5 @@ export const DiffRowView = memo(function DiffRowViewComponent({
     );
   }
 
-  return (
-    <box style={{ width: "100%", height: 1 }}>
-      <text fg={theme.muted}>Unsupported row.</text>
-    </box>
-  );
+  return unsupportedPlannedDiffRow(plannedRow);
 });

packages/hunk/src/ui/diff/codeRowLayout.ts

@@ -7,12 +7,13 @@ import {
 } from "./codeColumns";
 import { CODE_ROW_ADD_NOTE_BADGE_WIDTH } from "./codeRowAffordance";
 import type { DiffRow, RenderSpan } from "./diffRowModel";
-import type { PlannedReviewRow } from "./reviewRenderPlan";
+import {
+  createPlannedDiffReviewRow,
+  type PlannedDiffReviewRow,
+  type PlannedReviewRow,
+} from "./reviewRenderPlan";
 import { measureWrappedSpansLineCount } from "./styledSpanLayout";
 
-/** Planned review row that carries one terminal diff row. */
-export type PlannedDiffReviewRow = Extract<PlannedReviewRow, { kind: "diff-row" }>;
-
 /** Concrete width and wrapping decisions for one rendered code cell. */
 export interface CodeCellLayoutPlan {
   width: number;
@@ -186,16 +187,14 @@ export function legacyPlannedDiffRow(
   anchorId?: string,
   noteGuideSide?: "old" | "new",
 ): PlannedDiffReviewRow {
-  return {
-    kind: "diff-row",
+  return createPlannedDiffReviewRow(row, {
     key: row.key,
     stableKey: row.key,
     fileId: row.fileId,
     hunkIndex: row.hunkIndex,
-    row,
     anchorId,
     noteGuideSide,
-  };
+  });
 }
 
 /** Measure how many terminal rows one complete planned diff row occupies. */

packages/hunk/src/ui/diff/reviewRenderPlan.ts

@@ -22,18 +22,26 @@ interface InlineVisibleNotePlacement {
   noteIndex: number;
 }
 
+interface PlannedDiffReviewRowFields {
+  kind: "diff-row";
+  key: string;
+  stableKey: string;
+  stableAliasKeys?: string[];
+  fileId: string;
+  hunkIndex: number;
+  anchorId?: string;
+  noteGuideSide?: "old" | "new";
+}
+
+/** Planned review row carrying one terminal diff row subtype. */
+export type PlannedDiffReviewRow<Row extends DiffRow = DiffRow> = Row extends DiffRow
+  ? PlannedDiffReviewRowFields & { row: Row }
+  : never;
+
+export type PlannedDiffReviewRowInput = Omit<PlannedDiffReviewRowFields, "kind">;
+
 export type PlannedReviewRow =
-  | {
-      kind: "diff-row";
-      key: string;
-      stableKey: string;
-      stableAliasKeys?: string[];
-      fileId: string;
-      hunkIndex: number;
-      row: DiffRow;
-      anchorId?: string;
-      noteGuideSide?: "old" | "new";
-    }
+  | PlannedDiffReviewRow
   | {
       kind: "inline-note";
       key: string;
@@ -56,6 +64,53 @@ export type PlannedReviewRow =
       height: number;
     };
 
+/** Create a planned diff row while preserving its concrete row subtype. */
+export function createPlannedDiffReviewRow<Row extends DiffRow>(
+  row: Row,
+  fields: PlannedDiffReviewRowInput,
+): PlannedDiffReviewRow<Row>;
+export function createPlannedDiffReviewRow(
+  row: DiffRow,
+  fields: PlannedDiffReviewRowInput,
+): PlannedDiffReviewRow {
+  switch (row.type) {
+    case "collapsed":
+      return { kind: "diff-row", ...fields, row };
+    case "hunk-header":
+      return { kind: "diff-row", ...fields, row };
+    case "split-line":
+      return { kind: "diff-row", ...fields, row };
+    case "stack-line":
+      return { kind: "diff-row", ...fields, row };
+  }
+}
+
+/** Split or stack code row accepted by code-row rendering and interaction policy. */
+export type CodeDiffRow = Extract<DiffRow, { type: "split-line" | "stack-line" }>;
+
+/** Collapsed gap or hunk-header row accepted by metadata rendering. */
+export type DiffMetaRow = Extract<DiffRow, { type: "collapsed" | "hunk-header" }>;
+
+/** Planned review row carrying split or stack code cells. */
+export type PlannedCodeReviewRow = PlannedDiffReviewRow<CodeDiffRow>;
+
+/** Planned review row carrying metadata rather than code cells. */
+export type PlannedDiffMetaReviewRow = PlannedDiffReviewRow<DiffMetaRow>;
+
+/** Return whether a planned diff row carries renderable code cells. */
+export function isPlannedCodeReviewRow(
+  plannedRow: PlannedDiffReviewRow,
+): plannedRow is PlannedCodeReviewRow {
+  return plannedRow.row.type === "split-line" || plannedRow.row.type === "stack-line";
+}
+
+/** Return whether a planned diff row carries a gap or hunk header. */
+export function isPlannedDiffMetaReviewRow(
+  plannedRow: PlannedDiffReviewRow,
+): plannedRow is PlannedDiffMetaReviewRow {
+  return plannedRow.row.type === "collapsed" || plannedRow.row.type === "hunk-header";
+}
+
 function lineRows(rows: DiffRow[]) {
   return rows.filter(
     (row): row is DiffLineRow => row.type === "split-line" || row.type === "stack-line",
@@ -396,17 +451,17 @@ export function buildReviewRenderPlan({
       anchoredHunks.add(row.hunkIndex);
     }
 
-    plannedRows.push({
-      kind: "diff-row",
-      key: `diff-row:${row.key}`,
-      stableKey: diffStableKey,
-      stableAliasKeys: diffStableAliasKeys,
-      fileId: row.fileId,
-      hunkIndex: row.hunkIndex,
-      row,
-      anchorId,
-      noteGuideSide: noteGuideSideByRowKey.get(row.key),
-    });
+    plannedRows.push(
+      createPlannedDiffReviewRow(row, {
+        key: `diff-row:${row.key}`,
+        stableKey: diffStableKey,
+        stableAliasKeys: diffStableAliasKeys,
+        fileId: row.fileId,
+        hunkIndex: row.hunkIndex,
+        anchorId,
+        noteGuideSide: noteGuideSideByRowKey.get(row.key),
+      }),
+    );
 
     const anchoredNotes = placementsByAnchor.get(row.key) ?? [];
     anchoredNotes.forEach((placement) => {