rhg: support "!" syntax for disabling extensions

rhg: support "!" syntax for disabling extensions

This makes it so that calls in test-log.t do not fall back immediately because
of the disabled extension, instead going through the CLI parsing code, which
breaks because of invalid UTF-8 in a flag.

I *think* clap 3.x+ supports this? I'm not sure, and we have to upgrade the
minimum Rust version to use clap 3.x anyway which is out of scope for this
series, so let's just kick that can down the road a little bit.

--- a/rust/rhg/src/main.rs	Fri May 20 11:02:52 2022 +0100
+++ b/rust/rhg/src/main.rs	Mon Jul 11 17:27:39 2022 +0200
@@ -687,13 +687,18 @@
     }
 
     let enabled: HashSet<&[u8]> = config
-        .get_section_keys(b"extensions")
-        .into_iter()
-        .map(|extension| {
+        .iter_section(b"extensions")
+        .filter_map(|(extension, value)| {
+            if value == b"!" {
+                // Filter out disabled extensions
+                return None;
+            }
             // Ignore extension suboptions. Only `required` exists for now.
             // `rhg` either supports an extension or doesn't, so it doesn't
             // make sense to consider the loading of an extension.
-            extension.split_2(b':').unwrap_or((extension, b"")).0
+            let actual_extension =
+                extension.split_2(b':').unwrap_or((extension, b"")).0;
+            Some(actual_extension)
         })
         .collect();
 

--- a/tests/test-log.t	Fri May 20 11:02:52 2022 +0100
+++ b/tests/test-log.t	Mon Jul 11 17:27:39 2022 +0200
@@ -2157,6 +2157,8 @@
   ... '''.encode('utf-8')) and None
   $ sh < setup.sh
 
+#if no-rhg
+
 test in problematic encoding
   >>> with open('test.sh', 'wb') as f:
   ...     f.write(u'''
@@ -2179,6 +2181,8 @@
   3
   1
 
+#endif
+
   $ cd ..
 
 test hg log on non-existent files and on directories