Implement textDocument/documentHighlight

Author: AJenbo

docs/ARCHITECTURE.md

@@ -109,6 +109,8 @@ src/
 ├── references/
 │   ├── mod.rs              # Find References handler: same-file and cross-file symbol scanning
 │   └── tests.rs            # Unit tests for find-references
+├── highlight/
+│   └── mod.rs              # Document highlighting: same-file symbol occurrence highlighting
 ├── diagnostics/
 │   ├── mod.rs              # Diagnostic collection and publishing (skips vendor files)
 │   ├── deprecated.rs       # @deprecated usage diagnostics (strikethrough)
@@ -122,6 +124,7 @@ tests/
 ├── hover.rs                # Hover integration tests
 ├── signature_help.rs       # Signature help integration tests
 ├── implementation.rs       # Go-to-implementation integration tests
+├── document_highlight.rs   # Document highlighting integration tests
 ├── docblock_*.rs           # Docblock parsing and type tests
 ├── parser.rs               # PHP parser / AST extraction tests
 ├── composer.rs             # Composer integration tests

docs/CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Find References.** "Find All References" locates every usage of a symbol across the project. Supports classes, interfaces, traits, enums, methods, properties, constants, functions, and variables. Variable references are scoped to the enclosing function or closure. Cross-file scanning lazily indexes user files on demand (vendor and stub files are excluded, matching PhpStorm's behaviour). The workspace walk respects `.gitignore` rules, so generated/cached directories (blade cache, Symfony `var/cache/`, `node_modules/`, etc.) are automatically skipped.
 - **`#[Deprecated]` attribute support.** PHPantom now reads the `#[Deprecated]` attribute used by phpstorm-stubs (~362 elements) in addition to docblock `@deprecated` tags. The `reason` and `since` fields appear in hover, completion strikethrough, and deprecation diagnostics. When both a docblock tag and an attribute are present, the docblock message takes priority. Works on classes, interfaces, traits, enums, methods, properties, constants, and standalone functions.
 - **Deprecation diagnostics for variable member access.** Calling a deprecated method or accessing a deprecated property through a variable (e.g. `$svc->oldMethod()`) now produces a strikethrough diagnostic. Previously only `self::`, `static::`, `$this->`, and explicit class name accesses were checked.
+- **Document highlighting.** Placing the cursor on a symbol highlights all other occurrences in the current file. Variables are scoped to their enclosing function or closure. Assignment targets, parameters, foreach bindings, and catch variables are marked as writes; all other occurrences are reads. Class names, members, functions, and constants highlight file-wide.
 
 ### Changed
 

docs/todo.md

@@ -76,7 +76,6 @@ Each one removes a reason someone might look elsewhere.
 
 | # | Item | Effort | Domain | Doc Link |
 |---|---|---|---|---|
-| 18 | Document Highlighting (`textDocument/documentHighlight`) | Low | LSP Features | [lsp-features.md §2](todo/lsp-features.md#2-document-highlighting-textdocumentdocumenthighlight) |
 | 19 | Document Symbols (`textDocument/documentSymbol`) | Low | LSP Features | [lsp-features.md §4](todo/lsp-features.md#4-document-symbols-textdocumentdocumentsymbol) |
 | 20 | Workspace Symbols (`workspace/symbol`) | Low-Medium | LSP Features | [lsp-features.md §5](todo/lsp-features.md#5-workspace-symbols-workspacesymbol) |
 | 21 | Folding Ranges (`textDocument/foldingRange`) | Low | LSP Features | [lsp-features.md §12](todo/lsp-features.md#12-folding-ranges-textdocumentfoldingrange) |