diff rust/rhg/src/error.rs @ 49149:006688e36e12 stable

rhg: use `Command::exec` instead of `Command::status`

`rhg` is supposed to be a transparent executable, using a subprocess defeats
that purpose. See inline comments for more details.

This also introduces the `which` crate to check if the fallback executable
actually exists to help debugging (plain `execve` doesn't give much
information).

The error code 253 is used to signify that the fallback is not found, but may
mean in the future that it is otherwise invalid if we start being more
specific.

Differential Revision: https://phab.mercurial-scm.org/D12578

--- a/rust/rhg/src/error.rs	Wed Apr 27 15:47:57 2022 +0200
+++ b/rust/rhg/src/error.rs	Tue Apr 19 12:27:40 2022 +0200
@@ -29,6 +29,9 @@
     /// `rhg` may attempt to silently fall back to Python-based `hg`, which
     /// may or may not support this feature.
     UnsupportedFeature { message: Vec<u8> },
+    /// The fallback executable does not exist (or has some other problem if
+    /// we end up being more precise about broken fallbacks).
+    InvalidFallback { path: Vec<u8>, err: String },
 }
 
 impl CommandError {