MIDL Language Support for VS Code

A complete MIDL3 development environment — catch errors as you type, get context-aware completions, and ship correct WinRT APIs faster.

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⚡ Real-Time Diagnostics

Errors and warnings surface instantly as you type — no build step required. Syntax errors, undefined types, MIDL2/MIDL3 migration issues, and duplicate definitions are caught with precise source locations and actionable messages.

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🧠 Context-Aware IntelliSense

Completions adapt to where your cursor is. Inside an attribute bracket on a runtimeclass? You'll see activatable, composable, contract. Inside a struct body? Only value types that are valid there. Inside attribute arguments like [threading(|? You'll get sta, mta, both.

Includes WinRT primitives, collection/async types, external .winmd types, and trigger characters on . and space.

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🎯 Code Quality

16 built-in code quality rules with one-click quick fixers — enforce WinRT naming conventions, simplify verbose patterns, and catch common mistakes.

Async Naming Convention

Methods returning IAsyncOperation or IAsyncAction should follow the Async suffix convention. WinMIDL detects violations and offers one-click renames.

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🔗 Navigation

Go to Definition — F12 into Decompiled WinMD

F12 on any Windows SDK type jumps to a decompiled IDL view straight from the .winmd — no source code needed.

F2 Rename Symbol

Rename a symbol and all its references in one shot. Works across interface declarations, requires clauses, and return types.

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🌐 Windows SDK Integration

Namespace Drill-In

Type a dot after any Windows namespace and IntelliSense walks you through the hierarchy — Windows. → UI. → Composition, Core, Xaml…

Microsoft Learn Integration

Hover any Windows SDK type to see its documentation inline, with a direct link to Microsoft Learn. The side panel shows full API docs without leaving VS Code.

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Features

🎨 Syntax Highlighting

Full TextMate grammar covering both MIDL3 and classic MIDL syntax:

• Keywords — namespace, runtimeclass, interface, delegate, struct, enum, event, import, apicontract, and classic keywords like coclass, library, typedef, union
• Types — WinRT primitives (Boolean, Int32, String, Guid, Object, …) and classic types (HRESULT, BSTR, IUnknown, IDispatch, …)
• Qualified type names — Dotted names like Windows.Foundation.Uri highlighted as types
• Attributes — Keywords inside [...] brackets (e.g., uuid, contract, activatable, composable, threading, deprecated, and many more)
• GUIDs — Inline GUID literals colorized as constants
• Strings, numbers, comments — Double-quoted strings with escape sequences, hex (0xFF) and decimal literals, line (//) and block (/* */) comments
• Storage modifiers — static, partial, unsealed, protected, overridable, get, set, out, ref, const

📝 Code Snippets

19 snippets for common MIDL3 patterns — type a prefix and press Tab:

Prefix	Description
namespace	Namespace declaration
runtimeclass	Runtime class with default constructor
unsealedruntimeclass	Unsealed (composable) runtime class with base class
staticruntimeclass	Static-only runtime class
interface	Interface declaration
interfacerequires	Interface with requires clause
delegate	Delegate type
struct	Struct with fields
enum	Enumeration
flagsenum	Flags enumeration with [flags] attribute
propget	Read-only property ({ get; })
proprw	Read-write property (shorthand)
event	Typed event (TypedEventHandler)
asyncmethod	Async method returning IAsyncOperation<T>
asyncaction	Async method returning IAsyncAction
contract	Contract version attribute
apicontract	API contract definition with [contractversion]
versionedblock	Versioned member block with contract attribute
import	Import directive

🖱️ Hover Information

Hover over any token for contextual documentation — keywords, built-in types, user-defined types, and external .winmd symbols.

🔗 Go to Definition

Ctrl+Click or F12 on any type or member name to jump to its declaration. Also works on attribute names — F12 on [threading] or [contract] navigates to the SDK attribute type definition (decompiled from .winmd).

🔎 Find All References

Shift+F12 to find every usage of a symbol in the document.

✍️ Signature Help

Parameter hints triggered by ( and , — shows full method/constructor/delegate signatures with active parameter highlighting. Also works inside attribute arguments: [contract(| shows (ContractName, version), [composable(| shows (FactoryType, access, version), etc.

📂 Code Folding

Collapse namespaces, runtime classes, interfaces, structs, enums, and versioned blocks using the editor fold controls.

🎯 Semantic Highlighting

14 semantic token types with declaration/static modifiers — identifiers resolved against the compilation for precise highlighting.

📐 Document Formatting

Shift+Alt+F — consistent 4-space indentation, normalized spacing, blank lines between declarations, trailing whitespace cleanup.

📋 Document Outline

Hierarchical symbol tree in Outline view and Breadcrumbs — namespaces, types, and members.

🔢 Namespace Type Count Code Lens

Each namespace block shows a summary of its contained types — e.g., 2 enums, 3 classes, 1 interface.

📝 Doc Comments (///)

Triple-slash comments are parsed as XML doc comments:

• Hover shows <summary> text for documented types and members
• Autocomplete generates <param> and <returns> skeletons
• /doc CLI switch emits .xdc XML doc comment files

🖥️ Inactive Region Graying

Code inside #ifdef / #ifndef blocks that are inactive (based on defined macros) is rendered with reduced opacity. Configure active defines via midl.defines in settings.

📊 Interactive Class Diagram

Command: MIDL: Show Class Diagram

Generates a UML-style class diagram from the current IDL file:

• Color-coded type boxes (enum, struct, interface, class, delegate)
• UML inheritance and implementation arrows
• Drag nodes to rearrange the layout
• Right-click → Copy as PNG to clipboard
• Ctrl+scroll to zoom in/out

📄 Language Configuration

Comment toggling, bracket matching, auto-closing pairs, smart indentation, and doc comment continuation — all configured out of the box.

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Configuration

Setting	Type	Default	Description
midl.strictMode	boolean	true	Enable strict MIDL3 mode. Classic MIDL constructs (coclass, library, typedef, etc.) produce warnings. Disable for mixed MIDL2/MIDL3 codebases.
midl.codeQualityHints	boolean	true	Show code quality hints (naming conventions, empty types, etc.)
midl.useWindowsSdk	boolean	true	Automatically reference Windows.winmd from the installed Windows SDK for type completion and F12 navigation.
midl.windowsSdkVersion	string	"latest"	Windows SDK version to use. Use the MIDL: Select Windows SDK Version command to pick from installed versions.
midl.flatSdkTypeCompletions	boolean	false	Show all SDK types by short name in completions (e.g. Button, Control). When off, only namespace names appear and you drill in with dot notation.
midl.fetchSdkDocs	boolean	true	Fetch type descriptions from Microsoft Learn on hover. Requires internet access.
midl.inlineDocsBrowser	boolean	true	Open Microsoft Learn documentation in a VS Code side panel instead of the external browser.
midl.defines	array	[]	Preprocessor defines for inactive region detection (e.g., ["FEATURE_X", "DEBUG"]).
midl.serverPath	string	"midl"	Path to the MIDL CLI executable. The extension ships its own copy — you shouldn't need to change this unless using a custom build.

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Getting Started

1. Install the Extension

Install MIDL Language Support from the VS Code marketplace or from a .vsix package.

2. Open a .idl File

The extension activates automatically when you open any .idl file. All features — syntax highlighting, diagnostics, completions, hover, and more — are available immediately.

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Requirements

• VS Code 1.85+ — Minimum supported VS Code version

The extension ships a self-contained Native AOT binary — no .NET SDK or runtime installation required.

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Known Limitations

• Go to Definition — Works within the current file, across .idl files (via winmidl.json or // @ref: directives), and for external .winmd types (decompiled view)
• Full document sync — The entire document is re-sent and reparsed on every keystroke (incremental text sync planned)
• No refactoring — Code actions are available but full refactoring support is still growing

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License

MIT