Open the sign-in URL on Windows

Login Flow v2 cannot complete without a browser, and the launcher had
a branch for xdg-open, one for Android's Intent, and an honest
Unsupported error for everything else — which on Windows stranded the
flow on "approve the sign-in in your browser". rundll32
url.dll,FileProtocolHandler is ShellExecute on the URL and needs no
crate; chosen over cmd /C start, whose quoting of & in a query string
is a known trap. Not verified: Wine has no browser to open.

docs/traceability.md

@@ -10,7 +10,7 @@ Denominators are parsed from [`requirements.md`](requirements.md) at run time, n
 | Metric | Value |
 |---|---|
 | Source files scanned | 354 |
-| TRACES tags found | 1468 |
+| TRACES tags found | 1469 |
 | Requirements defined | 191 |
 | Requirements covered | 140 |
 | **Coverage** | **73.3%** (140/191) |
@@ -121,7 +121,7 @@ _None._
 | FR-PLAT-LIN-1 | [`core/dr-types/src/settings.rs:1`](../core/dr-types/src/settings.rs#L1), [`platform/dr-plat/src/dirs.rs:1`](../platform/dr-plat/src/dirs.rs#L1), [`platform/dr-plat/src/storage.rs:344`](../platform/dr-plat/src/storage.rs#L344), [`ui/dr-ui/src/lib.rs:1129`](../ui/dr-ui/src/lib.rs#L1129), [`ui/dr-ui/src/preset_store.rs:1`](../ui/dr-ui/src/preset_store.rs#L1), [`ui/dr-ui/src/settings_store.rs:1`](../ui/dr-ui/src/settings_store.rs#L1) |
 | FR-PLAT-LIN-2 | [`platform/dr-plat/src/display.rs:1`](../platform/dr-plat/src/display.rs#L1), [`platform/dr-plat/src/display/wayland.rs:1`](../platform/dr-plat/src/display/wayland.rs#L1), [`platform/dr-plat/src/display/x11.rs:1`](../platform/dr-plat/src/display/x11.rs#L1) |
 | FR-PLAT-WIN-1 | [`platform/dr-plat/src/dirs.rs:1`](../platform/dr-plat/src/dirs.rs#L1) |
-| FR-PLAT-WIN-2 | [`apps/darkroom-desktop/build.rs:1`](../apps/darkroom-desktop/build.rs#L1), [`apps/darkroom-desktop/src/main.rs:6`](../apps/darkroom-desktop/src/main.rs#L6) |
+| FR-PLAT-WIN-2 | [`apps/darkroom-desktop/build.rs:1`](../apps/darkroom-desktop/build.rs#L1), [`apps/darkroom-desktop/src/main.rs:6`](../apps/darkroom-desktop/src/main.rs#L6), [`ui/dr-ui/src/launch_ui.rs:819`](../ui/dr-ui/src/launch_ui.rs#L819) |
 | FR-PLAT-WIN-3 | [`apps/darkroom-desktop/src/main.rs:19`](../apps/darkroom-desktop/src/main.rs#L19) |
 | FR-PLG-2 | [`core/dr-pipeline/src/declared/decl.rs:1`](../core/dr-pipeline/src/declared/decl.rs#L1), [`core/dr-pipeline/src/declared/expr.rs:152`](../core/dr-pipeline/src/declared/expr.rs#L152), [`core/dr-pipeline/src/declared/expr.rs:1`](../core/dr-pipeline/src/declared/expr.rs#L1), [`core/dr-pipeline/src/declared/mod.rs:1`](../core/dr-pipeline/src/declared/mod.rs#L1), [`core/dr-pipeline/src/declared/mod.rs:82`](../core/dr-pipeline/src/declared/mod.rs#L82), [`core/dr-pipeline/src/descriptor.rs:15`](../core/dr-pipeline/src/descriptor.rs#L15), [`core/dr-pipeline/src/descriptor.rs:734`](../core/dr-pipeline/src/descriptor.rs#L734), [`core/dr-pipeline/src/operation.rs:232`](../core/dr-pipeline/src/operation.rs#L232), [`core/dr-pipeline/tests/declared_parity.rs:1`](../core/dr-pipeline/tests/declared_parity.rs#L1), [`core/dr-pipeline/tests/declared_parity.rs:240`](../core/dr-pipeline/tests/declared_parity.rs#L240), [`core/dr-pipeline/tests/declared_parity.rs:305`](../core/dr-pipeline/tests/declared_parity.rs#L305), [`core/dr-pipeline/tests/declared_parity.rs:358`](../core/dr-pipeline/tests/declared_parity.rs#L358), [`core/dr-pipeline/tests/declared_parity.rs:418`](../core/dr-pipeline/tests/declared_parity.rs#L418) |
 | FR-PLG-2d | [`core/dr-pipeline/src/declared/decl.rs:112`](../core/dr-pipeline/src/declared/decl.rs#L112), [`core/dr-pipeline/src/declared/decl.rs:154`](../core/dr-pipeline/src/declared/decl.rs#L154), [`core/dr-pipeline/src/declared/decl.rs:1`](../core/dr-pipeline/src/declared/decl.rs#L1), [`core/dr-pipeline/src/declared/decl.rs:422`](../core/dr-pipeline/src/declared/decl.rs#L422), [`core/dr-pipeline/src/declared/decl.rs:67`](../core/dr-pipeline/src/declared/decl.rs#L67), [`core/dr-pipeline/src/declared/mod.rs:1`](../core/dr-pipeline/src/declared/mod.rs#L1), [`core/dr-pipeline/src/declared/mod.rs:384`](../core/dr-pipeline/src/declared/mod.rs#L384), [`core/dr-pipeline/src/declared/mod.rs:403`](../core/dr-pipeline/src/declared/mod.rs#L403) |

ui/dr-ui/src/launch_ui.rs

@@ -816,9 +816,26 @@ fn open_in_browser(url: &str) -> std::io::Result<()> {
     {
         android_open_url(url).map_err(|e| std::io::Error::other(e))
     }
+    // TRACES: FR-PLAT-WIN-2
+    // `ShellExecute` by way of the shell's URL handler, which is what a
+    // double-click on a link does, and needs no crate: `rundll32
+    // url.dll,FileProtocolHandler` has opened the default browser since
+    // Windows 98 and is still what the platform documents for the purpose.
+    // Not `cmd /C start`, whose quoting of `&` in a query string is a
+    // well-known trap.
+    #[cfg(windows)]
+    {
+        std::process::Command::new("rundll32")
+            .args(["url.dll,FileProtocolHandler", url])
+            .stdout(std::process::Stdio::null())
+            .stderr(std::process::Stdio::null())
+            .spawn()
+            .map(|_| ())
+    }
     #[cfg(not(any(
         all(unix, not(target_os = "android"), not(target_os = "macos")),
-        target_os = "android"
+        target_os = "android",
+        windows
     )))]
     {
         let _ = url;