Log like a debug build on macOS, where a Mac user can find it

Nobody working on DarkRoom has a Mac, so every macOS build is in the hands
of someone who can send a log and cannot attach a debugger. Three changes
make that log worth sending:

- The desktop's default filter on macOS is `debug` for every `dr_*` crate,
  the desktop crate and `onnxruntime` (the runtime's own session log).
- The state directory — the log and crash records — is `~/Library/Logs`
  on macOS rather than the `~/.local/state` Finder hides; Console.app
  lists it. Config and data keep the Unix rules.
- A `diagnostic` cargo profile: release plus line tables, so a crash
  record's backtrace reads file:line. On macOS the tables are in the
  `.dSYM` beside the executable, which the bundle must keep.

platform/dr-plat/src/crash.rs

@@ -98,7 +98,8 @@ pub fn set_state_dir(dir: PathBuf) {
 
 /// Where this application keeps state that is neither configuration nor cache.
 ///
-/// `$XDG_STATE_HOME/darkroom`, falling back to `~/.local/state/darkroom`.
+/// `$XDG_STATE_HOME/darkroom`, falling back to `~/.local/state/darkroom` —
+/// `~/Library/Logs/darkroom` on macOS (`dirs`).
 /// State rather than cache because a crash record must survive the sweep that
 /// a cache directory exists to permit, and rather than config because it is
 /// not something the user edits.

platform/dr-plat/src/diagnostics.rs

@@ -46,6 +46,8 @@
 //!
 //! * Linux: `$XDG_STATE_HOME/darkroom/darkroom.log`, else
 //!   `~/.local/state/darkroom/darkroom.log`.
+//! * macOS: `$XDG_STATE_HOME/darkroom/darkroom.log`, else
+//!   `~/Library/Logs/darkroom/darkroom.log`, where Console.app lists it.
 //! * Android: `/sdcard/Android/data/paris.tourolle.darkroom/files/darkroom.log`,
 //!   which `adb pull` reads from an ordinary release build. See
 //!   [`crate::state`] for why not the internal directory, and

platform/dr-plat/src/dirs.rs

@@ -17,6 +17,11 @@
 //! | Unix default | `~/.config` | `~/.local/share` | `~/.local/state` |
 //! | Windows | `%APPDATA%` | `%LOCALAPPDATA%` | `%LOCALAPPDATA%`, then `state` |
 //! | Windows default | `%USERPROFILE%\AppData\Roaming` | `…\AppData\Local` | `…\AppData\Local` |
+//! | macOS default | `~/.config` | `~/.local/share` | `~/Library/Logs` |
+//!
+//! macOS follows the Unix rules except for the one directory a user is asked
+//! to find by hand: the log. Finder hides `~/.local`, and `~/Library/Logs`
+//! is where Console.app and a Mac user already look (docs/dev/macos.md).
 //!
 //! then `darkroom` under each. Config roams on Windows and the rest does not,
 //! which is the same split XDG makes between config and everything else, and
@@ -100,11 +105,18 @@ fn resolve(kind: Base, env: impl Fn(&str) -> Option<OsString>) -> PathBuf {
     }
 }
 
+/// Where state goes under `$HOME` when `XDG_STATE_HOME` does not say.
+const STATE_UNDER_HOME: &str = if cfg!(target_os = "macos") {
+    "Library/Logs"
+} else {
+    ".local/state"
+};
+
 fn xdg_base(kind: Base, env: &impl Fn(&str) -> Option<OsString>) -> Option<PathBuf> {
     let (var, under_home) = match kind {
         Base::Config => ("XDG_CONFIG_HOME", ".config"),
         Base::Data => ("XDG_DATA_HOME", ".local/share"),
-        Base::State => ("XDG_STATE_HOME", ".local/state"),
+        Base::State => ("XDG_STATE_HOME", STATE_UNDER_HOME),
     };
     absolute(env(var)).or_else(|| absolute(env("HOME")).map(|h| h.join(under_home)))
 }
@@ -150,7 +162,7 @@ mod tests {
         );
         assert_eq!(
             xdg_base(Base::State, &e),
-            Some(PathBuf::from("/home/someone/.local/state"))
+            Some(PathBuf::from("/home/someone").join(STATE_UNDER_HOME))
         );
     }
 
@@ -162,7 +174,7 @@ mod tests {
         let e = env(&[("XDG_STATE_HOME", "state"), ("HOME", "/home/someone")]);
         assert_eq!(
             xdg_base(Base::State, &e),
-            Some(PathBuf::from("/home/someone/.local/state"))
+            Some(PathBuf::from("/home/someone").join(STATE_UNDER_HOME))
         );
         assert_eq!(xdg_base(Base::State, &env(&[("HOME", "")])), None);
     }