C+
October 16, 2026 ·The C+ team

Announcing C+ 0.0.30

C+ 0.0.30 moves the Windows UI and agent stack to WinUI 3, brings native design-system parity across Apple, Android, Linux, and Windows, adds #target_feature and #bitcast to the compiler, tightens error and status checking in the standard library, and expands the package and tooling surface.

Like every C+ release, 0.0.30 compiles to native machine code through LLVM with no virtual machine and no garbage collector.

WinUI 3 on Windows

On Windows, the Facet and agent stacks now target WinUI 3 (Windows App SDK 1.6) through four packages:

  • winrt: foundational HSTRING, IInspectable, activation factories, and apartment initialization.
  • winui: typed WinRT COM vtable bindings for Microsoft.UI.Xaml.* controls, layouts, brushes, and events, with a zero-SDK C ABI stub (winui_c_abi.c) that builds against standard MinGW headers.
  • facet_winui: the Windows Facet backend (App, Window, NavigationView, TabView, CommandBar, MenuBar, ContentDialog, ScrollViewer, and Direct2D canvas).
  • agent_winui, agent_winui_mcp, and facet_agent_winui: the Windows agent surface and MCP bridge over live UIElement trees.

facet_runtime and facet_agent now dispatch to facet_winui and agent_winui on Windows. facet_win32 is deprecated on Windows and retained only for legacy compatibility.

Cross-platform design-system parity

Every Facet backend now renders through its platform's native design system from the same declarative @view tree:

  • macOS (facet_appkit) and iOS (facet_uikit): Liquid Glass materials (NSGlassEffectView on macOS 26+ with NSVisualEffectView fallback; UIVisualEffectView blur chrome on iOS), semantic colors, SF Symbols, and native springs.
  • Android (facet_android): Material 3 tonal surfaces, 28 dp dialog radii, pill buttons and badges, Material 3 typography and switches, and spring animator physics.
  • Linux (facet_gtk): Libadwaita / GNOME HIG surface hierarchy, semantic badge and progress colors, boxed lists, and 12 px card radii.
  • Windows (facet_winui): Fluent 2 / WinUI 3 Mica backdrop, acrylic overlays, and native Xaml controls.

In the shared @view grammar, scroll is now a container block (scroll { ... }, scroll_x { ... }, scroll_both { ... }), matching row, column, and stack. Attaching a trailing { ... } block to a leaf control (text, button, badge, spacer, divider, progress, and so on) is now rejected at compile time with E1010.

Compiler and language updates

#target_feature("NAME") and #bitcast::[T](v)

#target_feature("NAME") is a compile-time bool intrinsic that reports whether a CPU feature ("avx2", "fma", "avx512f", "neon", "dotprod", and others) is enabled for the active target by --target-cpu and --target-feature:

if #target_feature("avx2") {
    return dot_256(a, b, n);
}
return dot_128(a, b, n);

A feature belonging to another architecture evaluates to false; an unknown feature name is rejected with E0903.

Bit-preserving conversion between equal-width scalars (i8/u8, i16/u16/f16/bf16, i32/u32/f32, i64/u64/f64) is now the #bitcast::[T](v) intrinsic (introduced in 0.0.29), lowering to an LLVM bitcast or constant fold:

let bits: u32 = #bitcast::[u32](1.0f32);
let back: f32 = #bitcast::[f32](bits);

Width mismatches and non-scalar operands are rejected with E0310. The earlier f16::from_bits, bf16::from_bits, f32::from_bits, f64::from_bits, and .to_bits() methods have been removed.

Template checking on generic impl blocks

Generic impl blocks are now type-checked at template definition time before any concrete instantiation exists. Bad field accesses, undefined names, return type mismatches, and unsatisfied interface bounds inside a generic method body are caught immediately even when no caller instantiates the type.

Diagnostics and safety checks

  • W0009 (unused Status): discarding a status::Status return value as a bare statement now warns with W0009. Bind the result and check .is_ok(), or write let _ = ...; when discarding on purpose.
  • E0415 (export extern fn signature collision): declaring two export extern fn items with the same unmangled C symbol and different parameter or return types is now an error.
  • W0007 (non-UTF-8 string literal): string literals containing raw \xNN byte escapes that do not form valid UTF-8 now warn with W0007.
  • W0008 (redundant import): importing a module that is already in scope or never referenced warns with W0008.
  • Exhaustive guard let ... else Pattern: when a guard let names a complement pattern after else, the compiler verifies that the two patterns cover the enum without gaps (E0340) or overlap (E0350).

Standard library and packages

  • stdlib/path and stdlib/template: stdlib/path provides allocation-free str path slicing (basename, dirname, extension, stem, is_absolute) alongside owned join and with_extension. stdlib/template renders {{key}} placeholders with default HTML escaping and {{{raw}}} unescaped interpolation.
  • Total stdlib value producers: functions that construct and return a new Text or Vec (text::from_str, text::join, repeating, appending, replacing, pad_start, pad_end, str.split, vec::collect) return a valid empty value if an allocation fails partway through, rather than returning a truncated prefix.
  • appenv: application data, cache, config, state, log, runtime, and temporary directory resolution now live in the standalone appenv package. facet_runtime::app_data_dir() and facet_runtime::cache_dir() have been removed.
  • hybrid_web: unified around a single Page handle (load_url, load_html, eval_js, reload, back, forward, set_title_handler, set_load_handler). Each facet_* backend mounts a Page through mount_hybrid_web.

Tooling and agent sockets

  • Doctests accept ```cplus fences: cpc test now extracts doctests from both bare ``` and ```cplus doc-comment code fences. An unclosed C+ doc fence fails the test build instead of being silently skipped.
  • Per-UID agent socket directory: on macOS and Linux, agent_mcp places Unix-domain sockets inside /tmp/cplus-<uid>/ (0700) as cplus-agent-<pid>.sock. On Windows, agent_winui_mcp uses a named pipe (\\.\pipe\cplus-agent-<pid>).
  • LSP and MCP: added --log-file PATH for session tracing, improved hover docs and inlay hints, and added scope_at to cpc query and cpc mcp.

Install and read

brew update && brew upgrade cplus
cpc --version

Linux and Windows builds are available from the GitHub releases page. Read the C+ 0.0.30 manual and the complete release notes for the full list of changes and migration details. Earlier manuals remain archived under /docs/{version}.

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