Lumotia/docs/architecture-map/02-tauri-runtime/cargo-and-features.md

name, type, slice, last_verified

name	type	slice	last_verified
Cargo and features	architecture-map-page	02-tauri-runtime	2026/05/09

Cargo and features

Where you are: Architecture map → Tauri runtime → Cargo and features

Plain English summary. This page walks the Tauri crate's Cargo.toml, its build.rs, and its .cargo/config.toml. The crate is the binary entry for the desktop app and the library entry for the Android target. The whisper cargo feature is the kill-switch for the whisper.cpp backend. Per-target dependency blocks gate macOS objc2 bindings, Linux GTK / WebKitGTK, and Windows base64 (used by the TTS PowerShell shim). build.rs enforces the CSP regression guard documented in docs/whisper-ecosystem/brief.md item #2.

At a glance

• Path: src-tauri/Cargo.toml (108 LOC), src-tauri/build.rs (81 LOC), src-tauri/.cargo/config.toml (3 LOC).
• Tauri commands exposed: none. Build-system files only.
• Events emitted: none.
• Depends on: every workspace crate (slices 03–05) plus the Tauri ecosystem.
• Called from frontend at: nothing direct. The build outputs land in the dev / packaged binary.

What's in here

Cargo.toml

Package metadata: name = "lumotia", version = "0.1.0", description = "Lumotia — Think out loud", authors = ["CORBEL Ltd"], edition = "2021".

Lib stanza (src-tauri/Cargo.toml:8):

name       = "lumotia_lib"
crate-type = ["staticlib", "cdylib", "rlib"]

staticlib and cdylib are needed for the Android target where Tauri builds an .aar from a cdylib. rlib makes it consumable from main.rs.

[features]

default = ["whisper"]
whisper = ["lumotia-transcription/whisper"]

The whisper feature transitively enables lumotia-transcription/whisper. The crate-level default-features = false on lumotia-transcription (src-tauri/Cargo.toml:33) means a --no-default-features workspace build drops whisper-rs-sys entirely; Parakeet still works. commands::models::load_model_from_disk returns a clear runtime error for Engine::Whisper when the feature is off.

[build-dependencies]

tauri-build = "2", plus serde_json = "1" for the CSP regression guard in build.rs.

[dependencies] — workspace crates

lumotia-core
lumotia-audio
lumotia-transcription   { default-features = false }
lumotia-ai-formatting
lumotia-storage
lumotia-cloud-providers
lumotia-hotkey
lumotia-llm

The cloud-providers crate is referenced here even though no command file currently imports it. Likely reserved for the Phase-N upload flow that the diagnostic-report bundler hints at.

[dependencies] — Tauri

tauri                       = { version = "2" }
tauri-plugin-opener         = "2"
tauri-plugin-dialog         = "2"
tauri-plugin-notification   = "2"

These three plugins are unconditional. notification supports Android natively (Phase 6 nudges) so it stays out of the desktop-only block.

[dependencies] — runtime

serde       = { version = "1", features = ["derive"] }
serde_json  = "1"
tokio       = { version = "1", features = ["rt", "sync"] }
arboard     = "3.6.1"
sqlx        = { version = "0.8", default-features = false, features = ["runtime-tokio", "sqlite"] }
uuid        = { version = "1", features = ["v4"] }

The sqlx block has default-features = false and only opts into runtime-tokio and sqlite. lumotia-storage already pulls the macros / migrate / any / json features via its own re-export, so duplicating them here would just bloat compile time. sqlx is named directly because AppState types it as SqlitePool; naming a transitive dep type still requires the dep be listed.

[dev-dependencies]

tempfile = "3" for the Phase 9 commands::fs::write_text_file_cmd tests.

[target.'cfg(not(target_os = "android"))'.dependencies]

tauri                          = { version = "2", features = ["tray-icon"] }
tauri-plugin-global-shortcut   = "2"
tauri-plugin-window-state      = "2"
tauri-plugin-autostart         = "2"

Each is justified inline in src-tauri/Cargo.toml:74. Tray icons, global shortcuts, multi-window state, and autostart all either fail to compile against the Android NDK or are structurally meaningless on a single-window mobile activity. The Cargo gate matches the #[cfg(not(target_os = "android"))] blocks in lib.rs and commands/windows.rs.

Per-OS dependency blocks

linux:   webkit2gtk = "2.0", gtk = "0.18", gdk = "0.18"
macos:   objc2 = "0.6.4", objc2-foundation = { ... features = ["std", "NSString", "NSProcessInfo"] }
windows: base64 = "0.22"

• webkit2gtk/gtk/gdk are used in lib.rs (auto-grant audio capture) and commands/windows.rs (set GTK WindowTypeHint::Utility on the preview overlay). Versions track what webkit2gtk 2.0 transitively depends on.
• objc2 + objc2-foundation power the macOS App Nap power assertion (commands/power.rs::objc_bridge).
• base64 is the Windows TTS encoder. PowerShell -EncodedCommand requires UTF-16-LE base64.

build.rs

Two responsibilities:

1. Linker workaround. --allow-multiple-definition is passed to GNU ld / lld on Linux because llama-cpp-sys-2 and whisper-rs-sys both statically link their own copy of ggml, leading to duplicate symbols (src-tauri/build.rs:8). Documented as INTERIM; the intended fix is system-ggml shared-lib linking. Only emitted on Linux.
2. CSP regression guard. assert_loopback_llm_csp (src-tauri/build.rs:30) parses tauri.conf.json with serde_json, finds the connect-src directive (full-name match, not prefix), and asserts the four required tokens: http://127.0.0.1:* and ws://127.0.0.1:* must be present, http://localhost:* and ws://localhost:* must be absent. Fails compilation with a brief-item-#2 reference if any of those break. Re-runs when tauri.conf.json changes.

tauri_build::build() is called last. Order matters: the CSP guard fails fast, before tauri-build does any of its own work.

.cargo/config.toml

[env]
LIBCLANG_PATH = "C:\\Program Files\\LLVM\\bin"

Hard-coded Windows path so bindgen (used by Tauri 2's macros and a couple of dependencies) can find clang during a Windows build. Harmless on non-Windows hosts — the env var is just unused. Foot-gun: a Windows developer with Clang in a non-default path will have to override or remove this.

Data flow

• cargo build reads Cargo.toml, runs build.rs, then compiles src/lib.rs and src/main.rs. The CSP regression guard fires before any source compiles.
• The default features include whisper. A workspace-wide cargo build --no-default-features drops both whisper.cpp and the Tauri default features (which would also drop tray-icon, etc., so this is a niche build).
• Plugin crates land in the dependency graph and contribute permission manifests that gen/schemas/ is regenerated from at build time.

Watch-outs

• Adding a workspace crate dependency here also requires that crate to be in the root Cargo.toml's workspace members (or referenced by path = here, which is what is done now). All eight workspace crates appear in this Cargo.toml.
• The --allow-multiple-definition link arg is the kind of thing that hides bugs. If both ggml copies ever drift, the binary picks "the first definition" and the second copy's slightly-different symbol is silently shadowed. Track the whisper-rs-sys and llama-cpp-sys-2 ggml pins together.
• Bumping any of objc2, objc2-foundation, webkit2gtk, gtk, gdk is an ABI move. Test on each platform.
• The hard-coded LIBCLANG_PATH should ideally come from an environment variable or a build-script probe. Until then, document it in docs/dev-setup.md for Windows contributors.

See also

• App lifecycle — lib.rs::run is what consumes everything declared here.
• Tauri config — build.rs reads tauri.conf.json and pins the CSP shape.
• Tests — runtime regression for the same CSP property.
• Capabilities and ACL — gen/schemas/ files are regenerated when a plugin in this Cargo manifest changes.