Adds support for auto indentation to the JupyterLab Extension for MATLAB.

Author: philipc-mw

src/jupyter_matlab_labextension/.eslintrc.json

@@ -6,6 +6,9 @@
       "ecmaVersion": 6,
       "sourceType": "module"
   },
+  "env": {
+    "jest": true
+  },
   "plugins": ["@typescript-eslint"],
   "extends": ["standard"],
   "rules": {

src/jupyter_matlab_labextension/jest.config.js

@@ -0,0 +1,7 @@
+// Copyright 2025 The MathWorks, Inc.
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  testMatch: ['**/__tests__/**/*.ts?(x)', '**/?(*.)+(spec|test).ts?(x)'],
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
+};

src/jupyter_matlab_labextension/package.json

@@ -1,6 +1,6 @@
 {
   "name": "jupyter_matlab_labextension",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "description": "A JupyterLab extension.",
   "keywords": [
     "jupyter",
@@ -45,6 +45,8 @@
     "prettier:check": "jlpm prettier:base --check",
     "stylelint": "jlpm stylelint:check --fix",
     "stylelint:check": "stylelint --cache \"style/**/*.css\"",
+    "test": "jest && jlpm build:lezer && jlpm test:lezer",
+    "test:lezer": "cd src/lezer-matlab && npm test",
     "watch": "run-p watch:src watch:labextension",
     "watch:src": "tsc -w",
     "watch:labextension": "jupyter labextension watch .",
@@ -65,6 +67,7 @@
   },
   "devDependencies": {
     "@jupyterlab/builder": ">=4.0.0",
+    "@types/jest": "^29.5.14",
     "@typescript-eslint/eslint-plugin": "^5.62.0",
     "@typescript-eslint/parser": "^5.62.0",
     "cross-spawn": "^6.0.6",
@@ -75,10 +78,12 @@
     "eslint-plugin-n": "^15.0.0",
     "eslint-plugin-node": "^11.1.0",
     "eslint-plugin-promise": "^6.0.0",
+    "jest": "^29.7.0",
     "npm-run-all": "^4.1.5",
     "prettier": "^2.8.7",
     "rimraf": "^4.4.1",
     "semver": ">=5.7.2",
+    "ts-jest": "^29.2.5",
     "typescript": "~5.0.2",
     "ws": "^7.5.10",
     "yarn-audit-fix": "^10.1.1"

src/jupyter_matlab_labextension/src/codemirror-lang-matlab/codemirror-lang-matlab.ts

@@ -1,15 +1,35 @@
-// Copyright 2024 The MathWorks, Inc.
+// Copyright 2024-2025 The MathWorks, Inc.
 
 import { parser } from '../lezer-matlab/dist/index';
-import { LRLanguage, LanguageSupport } from '@codemirror/language';
+import { indentNodeProp, LanguageSupport, LRLanguage, TreeIndentContext } from '@codemirror/language';
+import { lineIndent, getDedentPattern } from './indent-matlab';
+
+function determineLineIndent (context: TreeIndentContext) {
+    if (context.pos === 0) { return null; }
+    const currentLine = context.lineAt(context.pos);
+    const previousLine = currentLine.text.length === 0
+        ? context.lineAt(context.pos, -1) // Look to the left of the simulated line break.
+        : context.lineAt(context.pos - 1); // Not on a simulated line break, so step back to the previous line.
+    if (previousLine === null || currentLine === null) {
+        return null;
+    }
+    return lineIndent(context.unit, currentLine.text, previousLine.text);
+}
 
 // Define a CodeMirror language from the Lezer parser.
 // https://codemirror.net/docs/ref/#language.LRLanguage
 export const matlabLanguage = LRLanguage.define({
     name: 'matlab',
-    parser,
+    parser: parser.configure({
+        props: [
+            indentNodeProp.add({
+                Script: determineLineIndent
+            })
+        ]
+    }),
     languageData: {
-        commentTokens: { line: '%' }
+        commentTokens: { line: '%' },
+        indentOnInput: getDedentPattern()
     }
 });
 

src/jupyter_matlab_labextension/src/codemirror-lang-matlab/indent-matlab.ts

@@ -0,0 +1,43 @@
+// Copyright 2025 The MathWorks, Inc.
+
+// Indent after these keywords unless the line ends with "end".
+const indentPattern = /^(?:\s*)(arguments|case|catch|classdef|else|elseif|enumeration|for|function|if|methods|otherwise|parfor|properties|switch|try|while)\b(?!.*\bend;?$)/;
+const dedentPattern = /^(?:\s*)(case|catch|else|end|otherwise)\b$/;
+const leadingWhitespacePattern = /^\s*/;
+
+export function getDedentPattern (): RegExp {
+    return new RegExp(dedentPattern);
+}
+
+export function lineIndent (indentUnit: number, currentLineText: string, previousLineText: string) {
+    const prevLeadingWhitespace = previousLineText.match(leadingWhitespacePattern);
+    const prevLineIndent = prevLeadingWhitespace ? prevLeadingWhitespace[0].length : 0;
+    if (currentLineText.match(/^(?:\s*)(case)\b$/) && previousLineText.match(/^(?:\s*)(switch)\b/)) {
+        // First case in a switch statement.
+        return prevLineIndent + indentUnit;
+    } else if (currentLineText.match(/^(?:\s*)(end)\b$/)) {
+        // Treat "end" separately to avoid mistakenly correcting the end of a switch statement.
+        const currentLeadingWhitespace = currentLineText.match(leadingWhitespacePattern);
+        const currentLineIndent = currentLeadingWhitespace ? currentLeadingWhitespace[0].length : 0;
+        const indentMatch = previousLineText.match(indentPattern);
+        if (indentMatch) {
+            return Math.min(prevLineIndent, currentLineIndent);
+        } else if (prevLineIndent >= indentUnit) {
+            return Math.min(prevLineIndent - indentUnit, currentLineIndent);
+        } else {
+            return 0;
+        }
+    } else {
+        // Other cases
+        let lineIndent = prevLineIndent;
+        const indentMatch = previousLineText.match(indentPattern);
+        if (indentMatch !== null) {
+            lineIndent += indentUnit;
+        }
+        const dedentMatch = currentLineText.match(dedentPattern);
+        if (dedentMatch !== null && lineIndent >= indentUnit) {
+            lineIndent -= indentUnit;
+        }
+        return lineIndent;
+    }
+}

src/jupyter_matlab_labextension/src/codemirror-lang-matlab/test/indent-matlab.test.ts

@@ -0,0 +1,49 @@
+// Copyright 2025 The MathWorks, Inc.
+
+import { lineIndent } from '../indent-matlab';
+
+describe('lineIndent', () => {
+    const indentUnit = 4;
+
+    test('should indent after an indent pattern', () => {
+        const previousLineText = 'if foo';
+        const currentLineText = '';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(indentUnit);
+    });
+
+    test('should indent first case in a switch statement by a single indent', () => {
+        const previousLineText = 'switch foo';
+        const currentLineText = 'case bar';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(indentUnit);
+    });
+
+    test('should dedent "end" after an indented block', () => {
+        const previousLineText = 'for c = 1:s';
+        const currentLineText = 'end';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(0);
+    });
+
+    test('should not change indentation for lines not matching patterns', () => {
+        const previousLineText = '    foo;';
+        const currentLineText = '';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(4);
+    });
+
+    test('should not indent after one-line statement', () => {
+        const previousLineText = 'if foo A=1; else A=2; end;';
+        const currentLineText = '';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(0);
+    });
+
+    test('should not decrease indentation below zero', () => {
+        const previousLineText = 'end';
+        const currentLineText = 'end';
+        const result = lineIndent(indentUnit, currentLineText, previousLineText);
+        expect(result).toBe(0);
+    });
+});

src/jupyter_matlab_labextension/src/lezer-matlab/src/matlab.grammar

@@ -1,4 +1,4 @@
-// Copyright 2024 The MathWorks, Inc.
+// Copyright 2024-2025 The MathWorks, Inc.
 
 @top Script { expression* }
 
@@ -24,7 +24,7 @@ expression {
   charVector { '"' (!["\n])* '"' }
   stringArray { "'" (!['\n])* "'" }
   SystemCommand { "!" (![\n])* }
-  Symbol { "+" | "-" | "*" | "=" | ";" | ":" | "(" | ")" | "{" | "}" | "[" | "]" }
+  Symbol { "+" | "-" | "*" | "=" | ";" | ":" | "(" | ")" | "{" | "}" | "[" | "]" | "," }
   space { @whitespace+ }
   @precedence { SystemCommand, Identifier }
   @precedence { SystemCommand, space }

src/jupyter_matlab_labextension/src/lezer-matlab/test/nested_terms.txt

@@ -78,4 +78,4 @@ Script(String,Symbol,String,Symbol)
 
 ==>
 
-Script(Magic, Magic, Magic)
+Script(Magic, Magic, Magic)

src/jupyter_matlab_labextension/tsconfig.json

@@ -19,7 +19,8 @@
     "strict": true,
     "strictNullChecks": true,
     "target": "es2018",
-    "types": []
+    "types": ["jest"],
+    "lib": ["DOM", "ES2018", "ES2020.Intl"]
   },
   "include": ["src"]
 }