refactor: Convert renderer typecheck methods to typeguards.

core/renderers/common/drawer.ts

@@ -14,7 +14,6 @@ import type {ExternalValueInput} from '../measurables/external_value_input.js';
 import type {Field} from '../measurables/field.js';
 import type {Icon} from '../measurables/icon.js';
 import type {InlineInput} from '../measurables/inline_input.js';
-import type {PreviousConnection} from '../measurables/previous_connection.js';
 import type {Row} from '../measurables/row.js';
 import {Types} from '../measurables/types.js';
 
@@ -117,13 +116,8 @@ export class Drawer {
         this.outlinePath_ += this.constants_.OUTSIDE_CORNERS.topLeft;
       } else if (Types.isRightRoundedCorner(elem)) {
         this.outlinePath_ += this.constants_.OUTSIDE_CORNERS.topRight;
-      } else if (
-        Types.isPreviousConnection(elem) &&
-        elem instanceof Connection
-      ) {
-        this.outlinePath_ += (
-          (elem as PreviousConnection).shape as Notch
-        ).pathLeft;
+      } else if (Types.isPreviousConnection(elem)) {
+        this.outlinePath_ += (elem.shape as Notch).pathLeft;
       } else if (Types.isHat(elem)) {
         this.outlinePath_ += this.constants_.START_HAT.path;
       } else if (Types.isSpacer(elem)) {
@@ -218,7 +212,7 @@ export class Drawer {
     let rightCornerYOffset = 0;
     let outlinePath = '';
     for (let i = elems.length - 1, elem; (elem = elems[i]); i--) {
-      if (Types.isNextConnection(elem) && elem instanceof Connection) {
+      if (Types.isNextConnection(elem)) {
         outlinePath += (elem.shape as Notch).pathRight;
       } else if (Types.isLeftSquareCorner(elem)) {
         outlinePath += svgPaths.lineOnAxis('H', bottomRow.xPos);
@@ -270,9 +264,9 @@ export class Drawer {
     for (let i = 0, row; (row = this.info_.rows[i]); i++) {
       for (let j = 0, elem; (elem = row.elements[j]); j++) {
         if (Types.isInlineInput(elem)) {
-          this.drawInlineInput_(elem as InlineInput);
+          this.drawInlineInput_(elem);
         } else if (Types.isIcon(elem) || Types.isField(elem)) {
-          this.layoutField_(elem as Field | Icon);
+          this.layoutField_(elem);
         }
       }
     }
@@ -296,13 +290,13 @@ export class Drawer {
     }
 
     if (Types.isIcon(fieldInfo)) {
-      const icon = (fieldInfo as Icon).icon;
+      const icon = fieldInfo.icon;
       icon.setOffsetInBlock(new Coordinate(xPos, yPos));
       if (this.info_.isInsertionMarker) {
         icon.hideForInsertionMarker();
       }
     } else {
-      const svgGroup = (fieldInfo as Field).field.getSvgRoot()!;
+      const svgGroup = fieldInfo.field.getSvgRoot()!;
       svgGroup.setAttribute(
         'transform',
         'translate(' + xPos + ',' + yPos + ')' + scale,

core/renderers/common/info.ts

@@ -672,20 +672,17 @@ export class RenderInfo {
       return row.yPos + elem.height / 2;
     }
     if (Types.isBottomRow(row)) {
-      const bottomRow = row as BottomRow;
-      const baseline =
-        bottomRow.yPos + bottomRow.height - bottomRow.descenderHeight;
+      const baseline = row.yPos + row.height - row.descenderHeight;
       if (Types.isNextConnection(elem)) {
         return baseline + elem.height / 2;
       }
       return baseline - elem.height / 2;
     }
     if (Types.isTopRow(row)) {
-      const topRow = row as TopRow;
       if (Types.isHat(elem)) {
-        return topRow.capline - elem.height / 2;
+        return row.capline - elem.height / 2;
       }
-      return topRow.capline + elem.height / 2;
+      return row.capline + elem.height / 2;
     }
     return row.yPos + row.height / 2;
   }

core/renderers/geras/drawer.ts

@@ -101,7 +101,7 @@ export class Drawer extends BaseDrawer {
   }
 
   override drawInlineInput_(input: InlineInput) {
-    this.highlighter_.drawInlineInput(input as InlineInput);
+    this.highlighter_.drawInlineInput(input);
 
     super.drawInlineInput_(input);
   }

core/renderers/geras/info.ts

@@ -10,16 +10,12 @@ import type {BlockSvg} from '../../block_svg.js';
 import type {Input} from '../../inputs/input.js';
 import {RenderInfo as BaseRenderInfo} from '../common/info.js';
 import type {Measurable} from '../measurables/base.js';
-import type {BottomRow} from '../measurables/bottom_row.js';
 import {DummyInput} from '../../inputs/dummy_input.js';
 import {EndRowInput} from '../../inputs/end_row_input.js';
 import {ExternalValueInput} from '../measurables/external_value_input.js';
-import type {Field} from '../measurables/field.js';
 import {InRowSpacer} from '../measurables/in_row_spacer.js';
-import type {InputRow} from '../measurables/input_row.js';
 import type {Row} from '../measurables/row.js';
 import {StatementInput} from '../../inputs/statement_input.js';
-import type {TopRow} from '../measurables/top_row.js';
 import {Types} from '../measurables/types.js';
 import {ValueInput} from '../../inputs/value_input.js';
 
@@ -151,7 +147,7 @@ export class RenderInfo extends BaseRenderInfo {
   override getInRowSpacing_(prev: Measurable | null, next: Measurable | null) {
     if (!prev) {
       // Between an editable field and the beginning of the row.
-      if (next && Types.isField(next) && (next as Field).isEditable) {
+      if (next && Types.isField(next) && next.isEditable) {
         return this.constants_.MEDIUM_PADDING;
       }
       // Inline input at the beginning of the row.
@@ -168,7 +164,7 @@ export class RenderInfo extends BaseRenderInfo {
     // Spacing between a non-input and the end of the row or a statement input.
     if (!Types.isInput(prev) && (!next || Types.isStatementInput(next))) {
       // Between an editable field and the end of the row.
-      if (Types.isField(prev) && (prev as Field).isEditable) {
+      if (Types.isField(prev) && prev.isEditable) {
         return this.constants_.MEDIUM_PADDING;
       }
       // Padding at the end of an icon-only row to make the block shape clearer.
@@ -209,7 +205,7 @@ export class RenderInfo extends BaseRenderInfo {
     // Spacing between a non-input and an input.
     if (!Types.isInput(prev) && next && Types.isInput(next)) {
       // Between an editable field and an input.
-      if (Types.isField(prev) && (prev as Field).isEditable) {
+      if (Types.isField(prev) && prev.isEditable) {
         if (Types.isInlineInput(next)) {
           return this.constants_.SMALL_PADDING;
         } else if (Types.isExternalInput(next)) {
@@ -234,7 +230,7 @@ export class RenderInfo extends BaseRenderInfo {
     // Spacing between an inline input and a field.
     if (Types.isInlineInput(prev) && next && Types.isField(next)) {
       // Editable field after inline input.
-      if ((next as Field).isEditable) {
+      if (next.isEditable) {
         return this.constants_.MEDIUM_PADDING;
       } else {
         // Noneditable field after inline input.
@@ -279,7 +275,7 @@ export class RenderInfo extends BaseRenderInfo {
       Types.isField(prev) &&
       next &&
       Types.isField(next) &&
-      (prev as Field).isEditable === (next as Field).isEditable
+      prev.isEditable === next.isEditable
     ) {
       return this.constants_.LARGE_PADDING;
     }
@@ -324,20 +320,17 @@ export class RenderInfo extends BaseRenderInfo {
       return row.yPos + elem.height / 2;
     }
     if (Types.isBottomRow(row)) {
-      const bottomRow = row as BottomRow;
-      const baseline =
-        bottomRow.yPos + bottomRow.height - bottomRow.descenderHeight;
+      const baseline = row.yPos + row.height - row.descenderHeight;
       if (Types.isNextConnection(elem)) {
         return baseline + elem.height / 2;
       }
       return baseline - elem.height / 2;
     }
     if (Types.isTopRow(row)) {
-      const topRow = row as TopRow;
       if (Types.isHat(elem)) {
-        return topRow.capline - elem.height / 2;
+        return row.capline - elem.height / 2;
       }
-      return topRow.capline + elem.height / 2;
+      return row.capline + elem.height / 2;
     }
 
     let result = row.yPos;
@@ -371,7 +364,7 @@ export class RenderInfo extends BaseRenderInfo {
       rowNextRightEdges.set(row, nextRightEdge);
       if (Types.isInputRow(row)) {
         if (row.hasStatement) {
-          this.alignStatementRow_(row as InputRow);
+          this.alignStatementRow_(row);
         }
         if (
           prevInput &&

core/renderers/measurables/in_row_spacer.ts

@@ -16,6 +16,14 @@ import {Types} from './types.js';
  * row.
  */
 export class InRowSpacer extends Measurable {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private inRowSpacer: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param width The width of the spacer.

core/renderers/measurables/input_row.ts

@@ -7,11 +7,7 @@
 // Former goog.module ID: Blockly.blockRendering.InputRow
 
 import type {ConstantProvider} from '../common/constants.js';
-
-import {ExternalValueInput} from './external_value_input.js';
-import {InputConnection} from './input_connection.js';
 import {Row} from './row.js';
-import {StatementInput} from './statement_input.js';
 import {Types} from './types.js';
 
 /**
@@ -41,12 +37,11 @@ export class InputRow extends Row {
     for (let i = 0; i < this.elements.length; i++) {
       const elem = this.elements[i];
       this.width += elem.width;
-      if (Types.isInput(elem) && elem instanceof InputConnection) {
-        if (Types.isStatementInput(elem) && elem instanceof StatementInput) {
+      if (Types.isInput(elem)) {
+        if (Types.isStatementInput(elem)) {
           connectedBlockWidths += elem.connectedBlockWidth;
         } else if (
           Types.isExternalInput(elem) &&
-          elem instanceof ExternalValueInput &&
           elem.connectedBlockWidth !== 0
         ) {
           connectedBlockWidths +=

core/renderers/measurables/jagged_edge.ts

@@ -16,6 +16,14 @@ import {Types} from './types.js';
  * collapsed block takes up during rendering.
  */
 export class JaggedEdge extends Measurable {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private jaggedEdge: undefined;
+
   /**
    * @param constants The rendering constants provider.
    */

core/renderers/measurables/next_connection.ts

@@ -17,6 +17,14 @@ import {Types} from './types.js';
  * up during rendering.
  */
 export class NextConnection extends Connection {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private nextConnection: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param connectionModel The connection object on the block that this

core/renderers/measurables/previous_connection.ts

@@ -17,6 +17,14 @@ import {Types} from './types.js';
  * up during rendering.
  */
 export class PreviousConnection extends Connection {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private previousConnection: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param connectionModel The connection object on the block that this

core/renderers/measurables/round_corner.ts

@@ -16,6 +16,14 @@ import {Types} from './types.js';
  * during rendering.
  */
 export class RoundCorner extends Measurable {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private roundCorner: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param opt_position The position of this corner.

core/renderers/measurables/row.ts

@@ -128,7 +128,7 @@ export class Row {
     for (let i = this.elements.length - 1; i >= 0; i--) {
       const elem = this.elements[i];
       if (Types.isInput(elem)) {
-        return elem as InputConnection;
+        return elem;
       }
     }
     return null;
@@ -167,8 +167,8 @@ export class Row {
   getFirstSpacer(): InRowSpacer | null {
     for (let i = 0; i < this.elements.length; i++) {
       const elem = this.elements[i];
-      if (Types.isSpacer(elem)) {
-        return elem as InRowSpacer;
+      if (Types.isInRowSpacer(elem)) {
+        return elem;
       }
     }
     return null;
@@ -182,8 +182,8 @@ export class Row {
   getLastSpacer(): InRowSpacer | null {
     for (let i = this.elements.length - 1; i >= 0; i--) {
       const elem = this.elements[i];
-      if (Types.isSpacer(elem)) {
-        return elem as InRowSpacer;
+      if (Types.isInRowSpacer(elem)) {
+        return elem;
       }
     }
     return null;

core/renderers/measurables/square_corner.ts

@@ -16,6 +16,14 @@ import {Types} from './types.js';
  * during rendering.
  */
 export class SquareCorner extends Measurable {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private squareCorner: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param opt_position The position of this corner.

core/renderers/measurables/statement_input.ts

@@ -18,6 +18,14 @@ import {Types} from './types.js';
  * during rendering
  */
 export class StatementInput extends InputConnection {
+  // This field exists solely to structurally distinguish this type from other
+  // Measurable subclasses. Because this class otherwise has the same fields as
+  // Measurable, and Typescript doesn't support nominal typing, Typescript will
+  // consider it and other subclasses in the same situation as being of the same
+  // type, even if typeguards are used, which could result in Typescript typing
+  // objects of this class as `never`.
+  private statementInput: undefined;
+
   /**
    * @param constants The rendering constants provider.
    * @param input The statement input to measure and store information for.

core/renderers/measurables/top_row.ts

@@ -8,8 +8,6 @@
 
 import type {BlockSvg} from '../../block_svg.js';
 import type {ConstantProvider} from '../common/constants.js';
-
-import {Hat} from './hat.js';
 import type {PreviousConnection} from './previous_connection.js';
 import {Row} from './row.js';
 import {Types} from './types.js';
@@ -86,7 +84,7 @@ export class TopRow extends Row {
       const elem = this.elements[i];
       width += elem.width;
       if (!Types.isSpacer(elem)) {
-        if (Types.isHat(elem) && elem instanceof Hat) {
+        if (Types.isHat(elem)) {
           ascenderHeight = Math.max(ascenderHeight, elem.ascenderHeight);
         } else {
           height = Math.max(height, elem.height);