Stop re-exporting basic diff types from gr-diff-line.ts Also replace 'FILE' by FILE and 'LOST' by LOST. This makes forking embed/diff/... easier. Release-Notes: skip Change-Id: Ief3784d6450694604c4e5156db0b6088e9f6b3c4

diff --git a/polygerrit-ui/app/api/diff.ts b/polygerrit-ui/app/api/diff.ts
index 4bf253d..8b3820e 100644
--- a/polygerrit-ui/app/api/diff.ts
+++ b/polygerrit-ui/app/api/diff.ts

@@ -302,11 +302,15 @@
   code_range: LineRange;
 }
 
-/** LOST LineNumber is for ported comments without a range, they have their own
- *  line number and are added on top of the FILE row in gr-diff
+/**
+ * LOST LineNumber is for ported comments without a range, they have their own
+ * line number and are added on top of the FILE row in <gr-diff>.
  */
 export declare type LineNumber = number | 'FILE' | 'LOST';
 
+export const FILE: LineNumber = 'FILE';
+export const LOST: LineNumber = 'LOST';
+
 /** The detail of the 'create-comment' event dispatched by gr-diff. */
 export declare interface CreateCommentEventDetail {
   side: Side;

diff --git a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts
index 75845f6..5c40050 100644
--- a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts
+++ b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list.ts

@@ -96,7 +96,7 @@
     return specialFilePathCompare(c1.path, c2.path);
   }
 
-  // Convert 'FILE' and 'LOST' to undefined.
+  // Convert FILE and LOST to undefined.
   const line1 = typeof c1.line === 'number' ? c1.line : undefined;
   const line2 = typeof c2.line === 'number' ? c2.line : undefined;
   if (line1 !== line2) {

diff --git a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list_test.ts b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list_test.ts
index a4357bb..3a06f8d 100644
--- a/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list_test.ts
+++ b/polygerrit-ui/app/elements/change/gr-thread-list/gr-thread-list_test.ts

@@ -41,6 +41,7 @@
 import {GrDropdownList} from '../../shared/gr-dropdown-list/gr-dropdown-list';
 import {fixture, html, assert} from '@open-wc/testing';
 import {GrCommentThread} from '../../shared/gr-comment-thread/gr-comment-thread';
+import {FILE} from '../../../api/diff';
 
 suite('gr-thread-list tests', () => {
   let element: GrThreadList;
@@ -665,7 +666,7 @@
 
   test('file level comment before line', () => {
     t1.line = 123;
-    t2.line = 'FILE';
+    t2.line = FILE;
     checkOrder([t2, t1]);
   });
 

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
index 2ccae8d..9650a14 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host.ts

@@ -53,7 +53,6 @@
 } from '../../../embed/diff/gr-diff/gr-diff';
 import {DiffViewMode, Side, CommentSide} from '../../../constants/constants';
 import {FilesWebLinks} from '../gr-patch-range-select/gr-patch-range-select';
-import {LineNumber, FILE} from '../../../embed/diff/gr-diff/gr-diff-line';
 import {GrCommentThread} from '../../shared/gr-comment-thread/gr-comment-thread';
 import {KnownExperimentId} from '../../../services/flags/flags';
 import {
@@ -71,7 +70,10 @@
 import {Subscription} from 'rxjs';
 import {
   DisplayLine,
+  FILE,
+  LineNumber,
   LineSelectedEventDetail,
+  LOST,
   RenderPreferences,
 } from '../../../api/diff';
 import {resolve} from '../../../models/dependency';
@@ -754,7 +756,7 @@
     const pointer = check.codePointers?.[0];
     assertIsDefined(pointer, 'code pointer of check result in diff');
     const line: LineNumber =
-      pointer.range?.end_line || pointer.range?.start_line || 'FILE';
+      pointer.range?.end_line || pointer.range?.start_line || FILE;
     const el = document.createElement('gr-diff-check-result');
     // This is what gr-diff expects, even though this is a check, not a comment.
     el.className = 'comment-thread';
@@ -1212,9 +1214,9 @@
     threadEl.showPortedComment = !!thread.ported;
     // These attributes are the "interface" between comment threads and gr-diff.
     // <gr-comment-thread> does not care about them and is not affected by them.
-    threadEl.setAttribute('slot', `${diffSide}-${thread.line || 'LOST'}`);
+    threadEl.setAttribute('slot', `${diffSide}-${thread.line || LOST}`);
     threadEl.setAttribute('diff-side', `${diffSide}`);
-    threadEl.setAttribute('line-num', `${thread.line || 'LOST'}`);
+    threadEl.setAttribute('line-num', `${thread.line || LOST}`);
     if (thread.range) {
       threadEl.setAttribute('range', `${JSON.stringify(thread.range)}`);
     }

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.ts b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.ts
index 045e2d0..4cf8356 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-host/gr-diff-host_test.ts

@@ -44,7 +44,12 @@
 } from '../../../types/common';
 import {CoverageType} from '../../../types/types';
 import {GrDiffHost, LineInfo} from './gr-diff-host';
-import {DiffInfo, DiffViewMode, IgnoreWhitespaceType} from '../../../api/diff';
+import {
+  DiffInfo,
+  DiffViewMode,
+  FILE,
+  IgnoreWhitespaceType,
+} from '../../../api/diff';
 import {ErrorCallback} from '../../../api/rest';
 import {SinonStub, SinonStubbedMember} from 'sinon';
 import {RunResult} from '../../../models/checks/checks-model';
@@ -1321,7 +1326,7 @@
   });
 
   test('filterThreadElsForLocation for file comments', () => {
-    const line: LineInfo = {beforeNumber: 'FILE', afterNumber: 'FILE'};
+    const line: LineInfo = {beforeNumber: FILE, afterNumber: FILE};
 
     const l = document.createElement('gr-comment-thread');
     l.setAttribute('diff-side', Side.LEFT);

diff --git a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
index c76f04c..e98d7d2 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment-thread/gr-comment-thread.ts

@@ -44,10 +44,9 @@
   UrlEncodedCommentId,
 } from '../../../types/common';
 import {CommentEditingChangedDetail, GrComment} from '../gr-comment/gr-comment';
-import {FILE} from '../../../embed/diff/gr-diff/gr-diff-line';
 import {GrButton} from '../gr-button/gr-button';
 import {DiffInfo, DiffPreferencesInfo} from '../../../types/diff';
-import {DiffLayer, RenderPreferences} from '../../../api/diff';
+import {DiffLayer, FILE, RenderPreferences} from '../../../api/diff';
 import {
   assert,
   assertIsDefined,

diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index 27a5590..74c5806 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts

@@ -55,7 +55,7 @@
 import {subscribe} from '../../lit/subscription-controller';
 import {ShortcutController} from '../../lit/shortcut-controller';
 import {classMap} from 'lit/directives/class-map.js';
-import {LineNumber} from '../../../api/diff';
+import {FILE, LineNumber} from '../../../api/diff';
 import {CommentSide, SpecialFilePath} from '../../../constants/constants';
 import {Subject} from 'rxjs';
 import {debounceTime} from 'rxjs/operators';
@@ -66,8 +66,6 @@
 import {userModelToken} from '../../../models/user/user-model';
 import {modalStyles} from '../../../styles/gr-modal-styles';
 
-const FILE = 'FILE';
-
 // visible for testing
 export const AUTO_SAVE_DEBOUNCE_DELAY_MS = 2000;
 

diff --git a/polygerrit-ui/app/embed/diff/gr-context-controls/gr-context-controls_test.ts b/polygerrit-ui/app/embed/diff/gr-context-controls/gr-context-controls_test.ts
index 8e2f432..215dc88 100644
--- a/polygerrit-ui/app/embed/diff/gr-context-controls/gr-context-controls_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-context-controls/gr-context-controls_test.ts

@@ -8,9 +8,14 @@
 import './gr-context-controls';
 import {GrContextControls} from './gr-context-controls';
 
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {GrDiffGroup, GrDiffGroupType} from '../gr-diff/gr-diff-group';
-import {DiffFileMetaInfo, DiffInfo, SyntaxBlock} from '../../../api/diff';
+import {
+  DiffFileMetaInfo,
+  DiffInfo,
+  GrDiffLineType,
+  SyntaxBlock,
+} from '../../../api/diff';
 import {fixture, html, assert} from '@open-wc/testing';
 import {waitEventLoop} from '../../../test/test-utils';
 

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-binary.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-binary.ts
index cc45e1e..7ace605 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-binary.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-binary.ts

@@ -8,6 +8,7 @@
 import {createElementDiff} from '../gr-diff/gr-diff-utils';
 import {GrDiffGroup} from '../gr-diff/gr-diff-group';
 import {html, render} from 'lit';
+import {FILE} from '../../../api/diff';
 
 export class GrDiffBuilderBinary extends GrDiffBuilder {
   constructor(
@@ -20,8 +21,8 @@
 
   override buildSectionElement(group: GrDiffGroup): HTMLElement {
     const section = createElementDiff('tbody', 'binary-diff');
-    // Do not create a diff row for 'LOST'.
-    if (group.lines[0].beforeNumber !== 'FILE') return section;
+    // Do not create a diff row for LOST.
+    if (group.lines[0].beforeNumber !== FILE) return section;
     return super.buildSectionElement(group);
   }
 

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element.ts
index 328b577..c1c6d15 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element.ts

@@ -27,9 +27,9 @@
   GrRangedCommentLayer,
 } from '../gr-ranged-comment-layer/gr-ranged-comment-layer';
 import {GrCoverageLayer} from '../gr-coverage-layer/gr-coverage-layer';
-import {DiffViewMode, RenderPreferences} from '../../../api/diff';
+import {DiffViewMode, LineNumber, RenderPreferences} from '../../../api/diff';
 import {createDefaultDiffPrefs, Side} from '../../../constants/constants';
-import {GrDiffLine, LineNumber} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {
   GrDiffGroup,
   GrDiffGroupType,

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element_test.ts
index da2e9f1..f6f0cb3 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-element_test.ts

@@ -11,12 +11,13 @@
 import './gr-diff-builder-element';
 import {stubBaseUrl, waitUntil} from '../../../test/test-utils';
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {
   DiffContent,
   DiffLayer,
   DiffPreferencesInfo,
   DiffViewMode,
+  GrDiffLineType,
   Side,
 } from '../../../api/diff';
 import {stubRestApi} from '../../../test/test-utils';

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-image.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-image.ts
index 1f7ffd3..59933c3 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-image.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-image.ts

@@ -5,7 +5,7 @@
  */
 import {ImageInfo} from '../../../types/common';
 import {DiffInfo, DiffPreferencesInfo} from '../../../types/diff';
-import {RenderPreferences, Side} from '../../../api/diff';
+import {FILE, RenderPreferences, Side} from '../../../api/diff';
 import '../gr-diff-image-viewer/gr-image-viewer';
 import {html, LitElement, nothing} from 'lit';
 import {customElement, property, query, state} from 'lit/decorators.js';
@@ -32,8 +32,8 @@
 
   override buildSectionElement(group: GrDiffGroup): HTMLElement {
     const section = createElementDiff('tbody');
-    // Do not create a diff row for 'LOST'.
-    if (group.lines[0].beforeNumber !== 'FILE') return section;
+    // Do not create a diff row for LOST.
+    if (group.lines[0].beforeNumber !== FILE) return section;
     return super.buildSectionElement(group);
   }
 

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder.ts
index f38ba5c..b0818e0 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder.ts

@@ -9,9 +9,9 @@
   ContentLoadNeededEventDetail,
   DiffContextExpandedExternalDetail,
   DiffViewMode,
+  LineNumber,
   RenderPreferences,
 } from '../../../api/diff';
-import {LineNumber} from '../gr-diff/gr-diff-line';
 import {GrDiffGroup} from '../gr-diff/gr-diff-group';
 import {BlameInfo} from '../../../types/common';
 import {DiffInfo, DiffPreferencesInfo} from '../../../types/diff';

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
index 9acda81..b898a37 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts

@@ -12,13 +12,16 @@
   Side,
   LineNumber,
   DiffLayer,
+  GrDiffLineType,
+  LOST,
+  FILE,
 } from '../../../api/diff';
 import {BlameInfo} from '../../../types/common';
 import {assertIsDefined} from '../../../utils/common-util';
 import {fire} from '../../../utils/event-util';
 import {getBaseUrl} from '../../../utils/url-util';
 import './gr-diff-text';
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {diffClasses, isResponsive} from '../gr-diff/gr-diff-utils';
 
 @customElement('gr-diff-row')
@@ -281,8 +284,8 @@
     lineNumber: LineNumber,
     side: Side
   ) {
-    if (this.hideFileCommentButton && lineNumber === 'FILE') return;
-    if (lineNumber === 'LOST') return;
+    if (this.hideFileCommentButton && lineNumber === FILE) return;
+    if (lineNumber === LOST) return;
     // .lineNumButton has `white-space: pre`, so prettier must not add spaces.
     // prettier-ignore
     return html`
@@ -298,18 +301,18 @@
           fire(this, 'line-mouse-enter', {lineNum: lineNumber, side})}
         @mouseleave=${() =>
           fire(this, 'line-mouse-leave', {lineNum: lineNumber, side})}
-      >${lineNumber === 'FILE' ? 'File' : lineNumber.toString()}</button>
+      >${lineNumber === FILE ? 'File' : lineNumber.toString()}</button>
     `;
   }
 
   private computeLineNumberAriaLabel(line: GrDiffLine, lineNumber: LineNumber) {
-    if (lineNumber === 'FILE') return 'Add file comment';
+    if (lineNumber === FILE) return 'Add file comment';
 
     // Add aria-labels for valid line numbers.
     // For unified diff, this method will be called with number set to 0 for
     // the empty line number column for added/removed lines. This should not
     // be announced to the screenreader.
-    if (lineNumber === 'LOST' || lineNumber <= 0) return undefined;
+    if (lineNumber === LOST || lineNumber <= 0) return undefined;
 
     switch (line.type) {
       case GrDiffLineType.REMOVE:
@@ -336,8 +339,8 @@
     const extras: string[] = [line.type, side];
     if (line.type !== GrDiffLineType.BLANK) extras.push('content');
     if (!line.hasIntralineInfo) extras.push('no-intraline-info');
-    if (line.beforeNumber === 'FILE') extras.push('file');
-    if (line.beforeNumber === 'LOST') extras.push('lost');
+    if (line.beforeNumber === FILE) extras.push('file');
+    if (line.beforeNumber === LOST) extras.push('lost');
 
     // .content has `white-space: pre`, so prettier must not add spaces.
     // prettier-ignore
@@ -437,7 +440,7 @@
   private renderText(side: Side) {
     const line = this.line(side);
     const lineNumber = this.lineNumber(side);
-    if (lineNumber === 'FILE' || lineNumber === 'LOST') return;
+    if (typeof lineNumber !== 'number') return;
 
     // Note that `this.layersApplied` will wipe away the <gr-diff-text>, and
     // another rendering cycle will be initiated in `updated()`.

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer_test.ts
index 8fd03bb..5651dcf 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/token-highlight-layer_test.ts

@@ -4,8 +4,12 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import '../../../test/common-test-setup';
-import {Side, TokenHighlightEventDetails} from '../../../api/diff';
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {
+  GrDiffLineType,
+  Side,
+  TokenHighlightEventDetails,
+} from '../../../api/diff';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {HOVER_DELAY_MS, TokenHighlightLayer} from './token-highlight-layer';
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
 import {html, render} from 'lit';

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-cursor/gr-diff-cursor.ts b/polygerrit-ui/app/embed/diff/gr-diff-cursor/gr-diff-cursor.ts
index 9e3640b..6a32afb 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-cursor/gr-diff-cursor.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-cursor/gr-diff-cursor.ts

@@ -8,6 +8,7 @@
 import {
   DiffViewMode,
   GrDiffCursor as GrDiffCursorApi,
+  GrDiffLineType,
   LineNumber,
   LineSelectedEventDetail,
 } from '../../../api/diff';
@@ -17,7 +18,6 @@
   GrCursorManager,
   isTargetable,
 } from '../../../elements/shared/gr-cursor-manager/gr-cursor-manager';
-import {GrDiffLineType} from '../gr-diff/gr-diff-line';
 import {GrDiffGroupType} from '../gr-diff/gr-diff-group';
 import {GrDiff} from '../gr-diff/gr-diff';
 import {fire} from '../../../utils/event-util';

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-diff-highlight.ts b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-diff-highlight.ts
index 69c0f5c..0d9250c 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-diff-highlight.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-diff-highlight.ts

@@ -11,7 +11,6 @@
 import {Side} from '../../../constants/constants';
 import {CommentRange} from '../../../types/common';
 import {GrSelectionActionBox} from '../gr-selection-action-box/gr-selection-action-box';
-import {FILE} from '../gr-diff/gr-diff-line';
 import {
   getLineElByChild,
   getLineNumberByChild,
@@ -308,7 +307,7 @@
     const side = getSideByLineEl(lineEl);
     if (!side) return null;
     const line = getLineNumberByChild(lineEl);
-    if (!line || line === FILE || line === 'LOST') return null;
+    if (typeof line !== 'number') return null;
     const contentTd = this.diffBuilder.getContentTdByLineEl(lineEl);
     if (!contentTd) return null;
     const contentText = contentTd.querySelector('.contentText');

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor.ts
index 05e5d3b..256dc11 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor.ts

@@ -3,13 +3,7 @@
  * Copyright 2016 Google LLC
  * SPDX-License-Identifier: Apache-2.0
  */
-import {
-  GrDiffLine,
-  GrDiffLineType,
-  FILE,
-  Highlights,
-  LineNumber,
-} from '../gr-diff/gr-diff-line';
+import {GrDiffLine, Highlights} from '../gr-diff/gr-diff-line';
 import {
   GrDiffGroup,
   GrDiffGroupType,
@@ -20,6 +14,7 @@
 import {debounce, DelayedTask} from '../../../utils/async-util';
 import {assert, assertIsDefined} from '../../../utils/common-util';
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
+import {FILE, GrDiffLineType, LOST, LineNumber} from '../../../api/diff';
 
 const WHOLE_FILE = -1;
 
@@ -130,7 +125,7 @@
 
     assertIsDefined(this.consumer, 'consumer');
     this.consumer.clearGroups();
-    this.consumer.addGroup(this.makeGroup('LOST'));
+    this.consumer.addGroup(this.makeGroup(LOST));
     this.consumer.addGroup(this.makeGroup(FILE));
 
     if (isBinary) return Promise.resolve();

diff --git a/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor_test.ts
index adcfff8..335f0d0 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-processor/gr-diff-processor_test.ts

@@ -5,11 +5,12 @@
  */
 import '../../../test/common-test-setup';
 import './gr-diff-processor';
-import {GrDiffLineType, FILE, GrDiffLine} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {GrDiffGroup, GrDiffGroupType} from '../gr-diff/gr-diff-group';
 import {GrDiffProcessor, State} from './gr-diff-processor';
 import {DiffContent} from '../../../types/diff';
 import {assert} from '@open-wc/testing';
+import {FILE, GrDiffLineType} from '../../../api/diff';
 
 suite('gr-diff-processor tests', () => {
   const WHOLE_FILE = -1;

diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group.ts
index 6d80d78..771e298 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group.ts

@@ -3,9 +3,8 @@
  * Copyright 2016 Google LLC
  * SPDX-License-Identifier: Apache-2.0
  */
-import {BLANK_LINE, GrDiffLine, GrDiffLineType} from './gr-diff-line';
-import {LineRange, Side} from '../../../api/diff';
-import {LineNumber} from './gr-diff-line';
+import {BLANK_LINE, GrDiffLine} from './gr-diff-line';
+import {GrDiffLineType, LineNumber, LineRange, Side} from '../../../api/diff';
 import {assertIsDefined, assert} from '../../../utils/common-util';
 import {untilRendered} from '../../../utils/dom-util';
 import {isDefined} from '../../../types/types';
@@ -133,12 +132,10 @@
     for (const line of group.lines) {
       if (
         (line.beforeNumber &&
-          line.beforeNumber !== 'FILE' &&
-          line.beforeNumber !== 'LOST' &&
+          typeof line.beforeNumber === 'number' &&
           line.beforeNumber < leftSplit) ||
         (line.afterNumber &&
-          line.afterNumber !== 'FILE' &&
-          line.afterNumber !== 'LOST' &&
+          typeof line.afterNumber === 'number' &&
           line.afterNumber < rightSplit)
       ) {
         before.push(line);
@@ -435,7 +432,7 @@
   }
 
   containsLine(side: Side, line: LineNumber) {
-    if (line === 'FILE' || line === 'LOST') {
+    if (typeof line !== 'number') {
       // For FILE and LOST, beforeNumber and afterNumber are the same
       return this.lines[0]?.beforeNumber === line;
     }
@@ -462,14 +459,8 @@
   }
 
   private _updateRangeWithNewLine(line: GrDiffLine) {
-    if (
-      line.beforeNumber === 'FILE' ||
-      line.afterNumber === 'FILE' ||
-      line.beforeNumber === 'LOST' ||
-      line.afterNumber === 'LOST'
-    ) {
-      return;
-    }
+    if (typeof line.beforeNumber !== 'number') return;
+    if (typeof line.afterNumber !== 'number') return;
 
     if (line.type === GrDiffLineType.ADD || line.type === GrDiffLineType.BOTH) {
       if (
@@ -505,8 +496,7 @@
     // untilRendered() promise.
     if (
       this.skip !== undefined ||
-      lineNumber === 'LOST' ||
-      lineNumber === 'FILE' ||
+      typeof lineNumber !== 'number' ||
       this.type === GrDiffGroupType.CONTEXT_CONTROL
     ) {
       return Promise.resolve();

diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group_test.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group_test.ts
index 7ead68f..bbbb4ad 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-group_test.ts

@@ -4,14 +4,14 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import '../../../test/common-test-setup';
-import {GrDiffLine, GrDiffLineType, BLANK_LINE} from './gr-diff-line';
+import {GrDiffLine, BLANK_LINE} from './gr-diff-line';
 import {
   GrDiffGroup,
   GrDiffGroupType,
   hideInContextControl,
 } from './gr-diff-group';
 import {assert} from '@open-wc/testing';
-import {Side} from '../../../api/diff';
+import {FILE, GrDiffLineType, LOST, Side} from '../../../api/diff';
 
 suite('gr-diff-group tests', () => {
   test('delta line pairs', () => {
@@ -297,18 +297,18 @@
 
     test('FILE', () => {
       const lines: GrDiffLine[] = [];
-      lines.push(new GrDiffLine(GrDiffLineType.BOTH, 'FILE', 'FILE'));
+      lines.push(new GrDiffLine(GrDiffLineType.BOTH, FILE, FILE));
       const group = new GrDiffGroup({type: GrDiffGroupType.DELTA, lines});
-      assert.equal(group.startLine(Side.LEFT), 'FILE');
-      assert.equal(group.startLine(Side.RIGHT), 'FILE');
+      assert.equal(group.startLine(Side.LEFT), FILE);
+      assert.equal(group.startLine(Side.RIGHT), FILE);
     });
 
     test('LOST', () => {
       const lines: GrDiffLine[] = [];
-      lines.push(new GrDiffLine(GrDiffLineType.BOTH, 'LOST', 'LOST'));
+      lines.push(new GrDiffLine(GrDiffLineType.BOTH, LOST, LOST));
       const group = new GrDiffGroup({type: GrDiffGroupType.DELTA, lines});
-      assert.equal(group.startLine(Side.LEFT), 'LOST');
-      assert.equal(group.startLine(Side.RIGHT), 'LOST');
+      assert.equal(group.startLine(Side.LEFT), LOST);
+      assert.equal(group.startLine(Side.RIGHT), LOST);
     });
   });
 });

diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-line.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-line.ts
index 338a275..1a89207 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-line.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-line.ts

@@ -4,17 +4,13 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {
+  FILE,
   GrDiffLine as GrDiffLineApi,
   GrDiffLineType,
   LineNumber,
   Side,
 } from '../../../api/diff';
 
-export {GrDiffLineType};
-export type {LineNumber};
-
-export const FILE = 'FILE';
-
 export class GrDiffLine implements GrDiffLineApi {
   constructor(
     readonly type: GrDiffLineType,

diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
index 669537e..927943c 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff-utils.ts

@@ -4,12 +4,14 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {BlameInfo, CommentRange} from '../../../types/common';
-import {FILE, LineNumber} from './gr-diff-line';
 import {Side} from '../../../constants/constants';
 import {DiffInfo} from '../../../types/diff';
 import {
   DiffPreferencesInfo,
   DiffResponsiveMode,
+  FILE,
+  LOST,
+  LineNumber,
   RenderPreferences,
 } from '../../../api/diff';
 import {getBaseUrl} from '../../../utils/url-util';
@@ -103,9 +105,7 @@
 }
 
 export function lineNumberToNumber(lineNumber?: LineNumber | null): number {
-  if (!lineNumber) return 0;
-  if (lineNumber === 'LOST') return 0;
-  if (lineNumber === 'FILE') return 0;
+  if (typeof lineNumber !== 'number') return 0;
   return lineNumber;
 }
 
@@ -138,15 +138,15 @@
   const lineNumberStr = lineEl.getAttribute('data-value');
   if (!lineNumberStr) return null;
   if (lineNumberStr === FILE) return FILE;
-  if (lineNumberStr === 'LOST') return 'LOST';
+  if (lineNumberStr === LOST) return LOST;
   const lineNumber = Number(lineNumberStr);
   return Number.isInteger(lineNumber) ? lineNumber : null;
 }
 
 export function getLine(threadEl: HTMLElement): LineNumber {
   const lineAtt = threadEl.getAttribute('line-num');
-  if (lineAtt === 'LOST') return lineAtt;
-  if (!lineAtt || lineAtt === 'FILE') return FILE;
+  if (lineAtt === LOST) return lineAtt;
+  if (!lineAtt || lineAtt === FILE) return FILE;
   const line = Number(lineAtt);
   if (isNaN(line)) throw new Error(`cannot parse line number: ${lineAtt}`);
   if (line < 1) throw new Error(`line number smaller than 1: ${line}`);

diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
index 3929330..38cb2ba 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff.ts

@@ -12,7 +12,6 @@
 import '../gr-syntax-themes/gr-syntax-theme';
 import '../gr-ranged-comment-themes/gr-ranged-comment-theme';
 import '../gr-ranged-comment-hint/gr-ranged-comment-hint';
-import {LineNumber} from './gr-diff-line';
 import {
   getLine,
   getLineElByChild,
@@ -54,6 +53,8 @@
   RenderPreferences,
   GrDiff as GrDiffApi,
   DisplayLine,
+  LineNumber,
+  LOST,
 } from '../../../api/diff';
 import {isSafari, toggleClass} from '../../../utils/dom-util';
 import {assertIsDefined} from '../../../utils/common-util';
@@ -617,7 +618,7 @@
     const el = e.target as Element;
 
     if (
-      el.getAttribute('data-value') !== 'LOST' &&
+      el.getAttribute('data-value') !== LOST &&
       (el.classList.contains('lineNum') ||
         el.classList.contains('lineNumButton'))
     ) {
@@ -980,7 +981,7 @@
       }
       const contentEl = this.diffBuilder.getContentTdByLineEl(lineEl);
       if (!contentEl) continue;
-      if (lineNum === 'LOST') {
+      if (lineNum === LOST) {
         this.insertPortedCommentsWithoutRangeMessage(contentEl);
       }
 

diff --git a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts
index 38eecfa..e2837ab 100644
--- a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts
+++ b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts

@@ -4,12 +4,13 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {strToClassName} from '../../../utils/dom-util';
 import {Side} from '../../../constants/constants';
 import {CommentRange} from '../../../types/common';
 import {DiffLayer, DiffLayerListener} from '../../../types/types';
 import {isLongCommentRange} from '../gr-diff/gr-diff-utils';
+import {GrDiffLineType} from '../../../api/diff';
 
 /**
  * Enhanced CommentRange by UI state. Interface for incoming ranges set from the
@@ -192,7 +193,7 @@
   // visible for testing
   getRangesForLine(line: GrDiffLine, side: Side): CommentRangeLineLayer[] {
     const lineNum = side === Side.LEFT ? line.beforeNumber : line.afterNumber;
-    if (lineNum === 'FILE' || lineNum === 'LOST') return [];
+    if (typeof lineNum !== 'number') return [];
     const ranges: CommentRangeLineLayer[] = this.rangesMap[side][lineNum] || [];
     return ranges.map(range => {
       // Make a copy, so that the normalization below does not mess with

diff --git a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts
index 7feda47..b90d6f7 100644
--- a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts

@@ -11,8 +11,8 @@
   GrRangedCommentLayer,
 } from './gr-ranged-comment-layer';
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
-import {GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
-import {Side} from '../../../api/diff';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
+import {GrDiffLineType, Side} from '../../../api/diff';
 import {SinonStub} from 'sinon';
 import {assert} from '@open-wc/testing';
 

diff --git a/polygerrit-ui/app/embed/diff/gr-syntax-layer/gr-syntax-layer-worker.ts b/polygerrit-ui/app/embed/diff/gr-syntax-layer/gr-syntax-layer-worker.ts
index da08a1f..baa2ab4 100644
--- a/polygerrit-ui/app/embed/diff/gr-syntax-layer/gr-syntax-layer-worker.ts
+++ b/polygerrit-ui/app/embed/diff/gr-syntax-layer/gr-syntax-layer-worker.ts

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 import {GrAnnotation} from '../gr-diff-highlight/gr-annotation';
-import {FILE, GrDiffLine, GrDiffLineType} from '../gr-diff/gr-diff-line';
+import {GrDiffLine} from '../gr-diff/gr-diff-line';
 import {DiffFileMetaInfo, DiffInfo} from '../../../types/diff';
 import {DiffLayer, DiffLayerListener} from '../../../types/types';
 import {Side} from '../../../constants/constants';
@@ -13,6 +13,8 @@
 import {HighlightService} from '../../../services/highlight/highlight-service';
 import {Provider} from '../../../models/dependency';
 import {ReportingService} from '../../../services/gr-reporting/gr-reporting';
+import {GrDiffLineType} from '../../../api/diff';
+import {assert} from '../../../utils/common-util';
 
 const LANGUAGE_MAP = new Map<string, string>([
   ['application/dart', 'dart'],
@@ -183,8 +185,8 @@
 
   annotate(el: HTMLElement, _: HTMLElement, line: GrDiffLine) {
     if (!this.enabled) return;
-    if (line.beforeNumber === FILE || line.afterNumber === FILE) return;
-    if (line.beforeNumber === 'LOST' || line.afterNumber === 'LOST') return;
+    if (typeof line.beforeNumber !== 'number') return;
+    if (typeof line.afterNumber !== 'number') return;
 
     let side: Side | undefined;
     if (
@@ -203,6 +205,7 @@
 
     const isLeft = side === Side.LEFT;
     const lineNumber = isLeft ? line.beforeNumber : line.afterNumber;
+    assert(typeof lineNumber === 'number', 'lineNumber must be a number');
     const rangesPerLine = isLeft ? this.leftRanges : this.rightRanges;
     const ranges = rangesPerLine[lineNumber - 1]?.ranges ?? [];
 

diff --git a/polygerrit-ui/app/utils/comment-util.ts b/polygerrit-ui/app/utils/comment-util.ts
index ee1a44c..f5649b6 100644
--- a/polygerrit-ui/app/utils/comment-util.ts
+++ b/polygerrit-ui/app/utils/comment-util.ts

@@ -36,6 +36,7 @@
 import {FormattedReviewerUpdateInfo} from '../types/types';
 import {extractMentionedUsers} from './account-util';
 import {assertIsDefined, uuid} from './common-util';
+import {FILE} from '../api/diff';
 
 export function isFormattedReviewerUpdate(
   message: ChangeMessage
@@ -173,7 +174,7 @@
       rootId: id(comment),
     };
     if (!comment.line && !comment.range) {
-      newThread.line = 'FILE';
+      newThread.line = FILE;
     }
     threads.push(newThread);
     if (id(comment)) idThreadMap[id(comment)] = newThread;

diff --git a/polygerrit-ui/app/utils/comment-util_test.ts b/polygerrit-ui/app/utils/comment-util_test.ts
index 7bf0c1e..713e6df 100644
--- a/polygerrit-ui/app/utils/comment-util_test.ts
+++ b/polygerrit-ui/app/utils/comment-util_test.ts

@@ -35,6 +35,7 @@
   UrlEncodedCommentId,
 } from '../types/common';
 import {assert} from '@open-wc/testing';
+import {FILE} from '../api/diff';
 
 suite('comment-util', () => {
   test('isUnresolved', () => {
@@ -213,7 +214,7 @@
       assert.equal(actualThreads[1].comments.length, 1);
       assert.deepEqual(actualThreads[1].comments[0], comments[2]);
       assert.equal(actualThreads[1].patchNum, 1 as RevisionPatchSetNum);
-      assert.equal(actualThreads[1].line, 'FILE');
+      assert.equal(actualThreads[1].line, FILE);
     });
 
     test('derives patchNum and range', () => {