rhg: add support for ignoring all extensions

Some workflows just want what `rhg` does and don't care about any extensions,
this makes it easier.

Differential Revision: https://phab.mercurial-scm.org/D12385

rust/rhg/src/main.rs

@@ -643,6 +643,11 b' const SUPPORTED_EXTENSIONS: &[&[u8]] ='
     &[b"blackbox", b"share", b"sparse", b"narrow", b"*"];
 
 fn check_extensions(config: &Config) -> Result<(), CommandError> {
+    if let Some(b"*") = config.get(b"rhg", b"ignored-extensions") {
+        // All extensions are to be ignored, nothing to do here
+        return Ok(());
+    }
+
     let enabled: HashSet<&[u8]> = config
         .get_section_keys(b"extensions")
         .into_iter()

tests/test-rhg.t

@@ -391,3 +391,17 b' The `:required` extension suboptions are'
   $ echo "*:required = yes" >> $HGRCPATH
   $ rhg files
   a
+
+We can ignore all extensions at once
+
+  $ echo "[extensions]" >> $HGRCPATH
+  $ echo "thisextensionbetternotexist=" >> $HGRCPATH
+  $ echo "thisextensionbetternotexisteither=" >> $HGRCPATH
+  $ $NO_FALLBACK rhg files
+  unsupported feature: extensions: thisextensionbetternotexist, thisextensionbetternotexisteither (consider adding them to 'rhg.ignored-extensions' config)
+  [252]
+
+  $ echo "[rhg]" >> $HGRCPATH
+  $ echo "ignored-extensions=*" >> $HGRCPATH
+  $ $NO_FALLBACK rhg files
+  a