feat(extraction): add Objective-C language support (#165)

Adds tree-sitter-objc extractor for `.m`/`.mm` files and `.h` files
that content-sniff as Objective-C (`@interface`/`@implementation`/`@protocol`/`@synthesize`).

Extraction covers:
- `@interface` / `@implementation` (deduplicated into a single class node)
- `@protocol` (as `protocol` nodes via new `interfaceKind` config)
- Methods with full multi-part selectors (`doThing:with:`, not just `doThing`),
  including `+`/`-` static distinction
- `@property` declarations
- Inheritance (`extends`) and protocol conformance (`implements`)
- C-style `function_definition` and `#import` (both `<system>` and `"local"` forms)
- Call edges from both `call_expression` and `message_expression`,
  with `self`/`super` skipped on qualified callee names

Two new generic hooks on `LanguageExtractor` (`resolveName`,
`extractPropertyName`) handle the cases where the default name walk
doesn't fit; usable by future languages with similar shape.

Import resolver tries `.h`, `.m`, `.mm` for `objc` imports.

Validated on AFNetworking (84 files, 100% file coverage), RestKit
(282 files, 99.6%), and Texture (926 files, 100%, heavy `.mm`
content) — multi-keyword selectors preserved up to 7 parts, no parse
failures on ObjC++.

Known limitations (disclosed in README):
- Categories produce duplicate class nodes (one per category file)
- Chained/nested message sends record only the innermost method
- `[Class alloc]` patterns don't emit `instantiates` edges
- `@protocol Foo <Bar>` refinement lists not yet wired to `implements`
- Heavy C++ in `.mm` files may parse incompletely under the ObjC grammar

src/extraction/languages/index.ts

@@ -25,6 +25,7 @@ import { pascalExtractor } from './pascal';
 import { scalaExtractor } from './scala';
 import { luaExtractor } from './lua';
 import { luauExtractor } from './luau';
+import { objcExtractor } from './objc';
 
 export const EXTRACTORS: Partial<Record<Language, LanguageExtractor>> = {
   typescript: typescriptExtractor,
@@ -47,4 +48,5 @@ export const EXTRACTORS: Partial<Record<Language, LanguageExtractor>> = {
   scala: scalaExtractor,
   lua: luaExtractor,
   luau: luauExtractor,
+  objc: objcExtractor,
 };

src/extraction/languages/objc.ts

@@ -0,0 +1,136 @@
+import type { Node as SyntaxNode } from 'web-tree-sitter';
+import { getChildByField, getNodeText } from '../tree-sitter-helpers';
+import type { ExtractorContext, LanguageExtractor } from '../tree-sitter-types';
+
+function findCompoundStatement(node: SyntaxNode): SyntaxNode | null {
+  for (let i = 0; i < node.namedChildCount; i++) {
+    const child = node.namedChild(i);
+    if (child?.type === 'compound_statement') {
+      return child;
+    }
+  }
+  return null;
+}
+
+/** Build ObjC selector: `greet`, `doThing:`, or `doThing:with:`. */
+function extractObjcMethodName(node: SyntaxNode, source: string): string | undefined {
+  if (node.type !== 'method_definition' && node.type !== 'method_declaration') {
+    return undefined;
+  }
+
+  const identifiers = node.namedChildren.filter((c) => c.type === 'identifier');
+  if (identifiers.length === 0) return undefined;
+
+  const hasParameters = node.namedChildren.some((c) => c.type === 'method_parameter');
+  const firstIdentifier = identifiers[0];
+  if (!firstIdentifier) return undefined;
+  if (!hasParameters) {
+    return getNodeText(firstIdentifier, source);
+  }
+
+  return identifiers.map((id) => `${getNodeText(id, source)}:`).join('');
+}
+
+function extractObjcPropertyName(node: SyntaxNode, source: string): string | null {
+  if (node.type !== 'property_declaration') return null;
+
+  const structDecl = node.namedChildren.find((c) => c.type === 'struct_declaration');
+  if (!structDecl) return null;
+
+  const structDeclarator = structDecl.namedChildren.find((c) => c.type === 'struct_declarator');
+  if (!structDeclarator) return null;
+
+  let current: SyntaxNode | null = structDeclarator;
+  while (current) {
+    const inner: SyntaxNode | undefined =
+      getChildByField(current, 'declarator') ||
+      current.namedChildren.find((c) => c.type === 'identifier' || c.type === 'pointer_declarator');
+    if (!inner) break;
+    if (inner.type === 'identifier') {
+      return getNodeText(inner, source);
+    }
+    current = inner;
+  }
+
+  return null;
+}
+
+export const objcExtractor: LanguageExtractor = {
+  functionTypes: ['function_definition'],
+  // Only @interface emits a class node; @implementation reuses it via visitNode.
+  classTypes: ['class_interface'],
+  methodTypes: ['method_definition'],
+  interfaceTypes: ['protocol_declaration'],
+  interfaceKind: 'protocol',
+  structTypes: ['struct_specifier'],
+  enumTypes: ['enum_specifier'],
+  enumMemberTypes: ['enumerator'],
+  typeAliasTypes: ['type_definition'],
+  importTypes: ['preproc_include'],
+  callTypes: ['call_expression', 'message_expression'],
+  variableTypes: ['declaration'],
+  propertyTypes: ['property_declaration'],
+  nameField: 'declarator',
+  bodyField: 'body',
+  paramsField: 'parameters',
+  resolveName: extractObjcMethodName,
+  extractPropertyName: extractObjcPropertyName,
+  resolveBody: (node, bodyField) => {
+    const fromField = getChildByField(node, bodyField);
+    if (fromField) {
+      return fromField;
+    }
+    return findCompoundStatement(node);
+  },
+  resolveTypeAliasKind: (node, _source) => {
+    for (let i = 0; i < node.namedChildCount; i++) {
+      const child = node.namedChild(i);
+      if (!child) continue;
+      if (child.type === 'enum_specifier' && getChildByField(child, 'body')) return 'enum';
+      if (child.type === 'struct_specifier' && getChildByField(child, 'body')) return 'struct';
+    }
+    return undefined;
+  },
+  isStatic: (node) => /^\s*\+/.test(node.text),
+  visitNode: (node, ctx: ExtractorContext) => {
+    if (node.type !== 'class_implementation') return false;
+
+    const classNameNode = node.namedChildren.find((c) => c.type === 'identifier');
+    if (!classNameNode) return true;
+
+    const className = getNodeText(classNameNode, ctx.source);
+    const classNode =
+      ctx.nodes.find(
+        (n) => n.name === className && n.filePath === ctx.filePath && n.kind === 'class'
+      ) ?? ctx.createNode('class', className, node, {});
+    if (!classNode) return true;
+
+    ctx.pushScope(classNode.id);
+    for (let i = 0; i < node.namedChildCount; i++) {
+      const child = node.namedChild(i);
+      if (child?.type === 'implementation_definition') {
+        for (let j = 0; j < child.namedChildCount; j++) {
+          const implChild = child.namedChild(j);
+          if (implChild) ctx.visitNode(implChild);
+        }
+      }
+    }
+    ctx.popScope();
+    return true;
+  },
+  extractImport: (node, source) => {
+    const importText = source.substring(node.startIndex, node.endIndex).trim();
+    const systemLib = node.namedChildren.find((c: SyntaxNode) => c.type === 'system_lib_string');
+    if (systemLib) {
+      return { moduleName: getNodeText(systemLib, source).replace(/^<|>$/g, ''), signature: importText };
+    }
+    const stringLiteral = node.namedChildren.find((c: SyntaxNode) => c.type === 'string_literal');
+    if (stringLiteral) {
+      const stringContent = stringLiteral.namedChildren.find((c: SyntaxNode) => c.type === 'string_content');
+      if (stringContent) {
+        return { moduleName: getNodeText(stringContent, source), signature: importText };
+      }
+    }
+    return null;
+  },
+};