feat: Add core.largeFileThreshold config for TextMate large file mode

spec/text-mate-language-mode-spec.js

@@ -51,6 +51,48 @@ describe('TextMateLanguageMode', () => {
     });
   });
 
+  describe('editor.largeFileThreshold config', () => {
+    afterEach(() => {
+      config.unset('editor.largeFileThreshold');
+    });
+
+    it('uses the configured threshold to determine large file mode', () => {
+      config.set('editor.largeFileThreshold', 0.001); // 1KB
+      const line = 'a b c d\n';
+      buffer = new TextBuffer(line.repeat(200)); // ~1.6KB
+      languageMode = new TextMateLanguageMode({
+        buffer,
+        config,
+        grammar: atom.grammars.grammarForScopeName('source.js')
+      });
+      expect(languageMode.largeFileMode).toBe(true);
+    });
+
+    it('disables automatic large file mode when threshold is 0', () => {
+      config.set('editor.largeFileThreshold', 0);
+      const line = 'a b c d\n';
+      buffer = new TextBuffer(line.repeat(256 * 1024)); // 2MB
+      languageMode = new TextMateLanguageMode({
+        buffer,
+        config,
+        grammar: atom.grammars.grammarForScopeName('source.js')
+      });
+      expect(languageMode.largeFileMode).toBe(false);
+    });
+
+    it('respects explicit largeFileMode param over config', () => {
+      config.set('editor.largeFileThreshold', 0);
+      buffer = new TextBuffer('small file');
+      languageMode = new TextMateLanguageMode({
+        buffer,
+        config,
+        grammar: atom.grammars.grammarForScopeName('source.js'),
+        largeFileMode: true
+      });
+      expect(languageMode.largeFileMode).toBe(true);
+    });
+  });
+
   describe('tokenizing', () => {
     describe('when the buffer is destroyed', () => {
       beforeEach(() => {

src/config-schema.js

@@ -455,6 +455,13 @@ const configSchema = {
         type: ['string', 'null']
       },
       // These can be used as globals or scoped, thus defaults.
+      largeFileThreshold: {
+        description:
+          'Files larger than this size in megabytes will open in large file mode with syntax highlighting disabled. Only applies to TextMate grammars; Tree-sitter grammars handle large files efficiently without this limitation. Set to 0 to always enable syntax highlighting regardless of file size.',
+        type: 'number',
+        default: 2,
+        minimum: 0
+      },
       fontFamily: {
         type: 'string',
         default: 'Menlo, Consolas, DejaVu Sans Mono, monospace',

src/text-mate-language-mode.js

@@ -29,17 +29,16 @@ class TextMateLanguageMode {
     this.tokenizationStarted = false;
     this.id = params.id != null ? params.id : nextId++;
     this.buffer = params.buffer;
-    this.largeFileMode = params.largeFileMode;
     this.config = params.config ?? atom.config;
-    this.largeFileMode =
-      params.largeFileMode != null
-        ? params.largeFileMode
-        : this.buffer.buffer.getLength() >= 2 * 1024 * 1024;
-
     this.grammar = params.grammar || NullGrammar;
     this.rootScopeDescriptor = new ScopeDescriptor({
       scopes: [this.grammar.scopeName]
     });
+    const largeFileThreshold = this.config.get('editor.largeFileThreshold', { scope: this.rootScopeDescriptor }) ?? 2;
+    this.largeFileMode =
+      params.largeFileMode != null
+        ? params.largeFileMode
+        : largeFileThreshold > 0 && this.buffer.buffer.getLength() >= largeFileThreshold * 1024 * 1024;
     this.disposables.add(
       this.grammar.onDidUpdate(() => this.retokenizeLines())
     );