feat: add fetch::Arguments::add_feature() for unconditional additions of arguments that are supposed to be features.

This differentiation is important to support V1 and V2 correctly, which have a different notion of features with V1
special-casing them, and V2 just sees everything as arguments.

Author: Byron

gix-protocol/src/fetch/arguments/blocking_io.rs

@@ -45,9 +45,7 @@ impl Arguments {
                 }
                 transport.invoke(
                     Command::Fetch.as_str(),
-                    self.features
-                        .iter()
-                        .filter_map(|(k, v)| v.as_ref().map(|v| (*k, Some(v.as_ref())))),
+                    self.features.iter().filter(|(_, v)| v.is_some()).cloned(),
                     Some(std::mem::replace(&mut self.args, retained_state).into_iter()),
                 )
             }

gix-protocol/src/fetch/arguments/mod.rs

@@ -165,20 +165,30 @@ impl Arguments {
     pub fn use_include_tag(&mut self) {
         debug_assert!(self.supports_include_tag, "'include-tag' feature required");
         if self.supports_include_tag {
-            match self.version {
-                gix_transport::Protocol::V0 | gix_transport::Protocol::V1 => {
-                    let features = self
-                        .features_for_first_want
-                        .as_mut()
-                        .expect("call use_include_tag before want()");
-                    features.push("include-tag".into())
-                }
-                gix_transport::Protocol::V2 => {
-                    self.args.push("include-tag".into());
-                }
+            self.add_feature("include-tag");
+        }
+    }
+
+    /// Add the given `feature`, unconditionally.
+    ///
+    /// Note that sending an unknown or unsupported feature may cause the remote to terminate
+    /// the connection. Use this method if you know what you are doing *and* there is no specialized
+    /// method for this, e.g. [`Self::use_include_tag()`].
+    pub fn add_feature(&mut self, feature: &str) {
+        match self.version {
+            gix_transport::Protocol::V0 | gix_transport::Protocol::V1 => {
+                let features = self
+                    .features_for_first_want
+                    .as_mut()
+                    .expect("call add_feature before first want()");
+                features.push(feature.into())
+            }
+            gix_transport::Protocol::V2 => {
+                self.args.push(feature.into());
             }
         }
     }
+
     fn prefixed(&mut self, prefix: &str, value: impl fmt::Display) {
         self.args.push(format!("{prefix}{value}").into());
     }

gix-protocol/src/fetch/tests.rs

@@ -319,6 +319,7 @@ mod arguments {
             assert!(arguments.is_stateless(true), "V2 is stateless…");
             assert!(arguments.is_stateless(false), "…in all cases");
 
+            arguments.add_feature("no-progress");
             arguments.deepen(1);
             arguments.deepen_relative();
             arguments.want(id("7b333369de1221f9bfbbe03a3a13e9a09bc1c907"));
@@ -329,6 +330,7 @@ mod arguments {
                 b"0012command=fetch
 0001000ethin-pack
 000eofs-delta
+0010no-progress
 000ddeepen 1
 0014deepen-relative
 0032want 7b333369de1221f9bfbbe03a3a13e9a09bc1c907
@@ -347,6 +349,7 @@ mod arguments {
                 let mut t = transport(&mut out, *is_stateful);
                 let mut arguments = arguments_v2(Some("shallow"));
 
+                arguments.add_feature("no-progress");
                 arguments.deepen(1);
                 arguments.deepen_since(12345);
                 arguments.shallow(id("7b333369de1221f9bfbbe03a3a13e9a09bc1c9ff"));
@@ -362,6 +365,7 @@ mod arguments {
                     b"0012command=fetch
 0001000ethin-pack
 000eofs-delta
+0010no-progress
 000ddeepen 1
 0017deepen-since 12345
 0035shallow 7b333369de1221f9bfbbe03a3a13e9a09bc1c9ff
@@ -371,6 +375,7 @@ mod arguments {
 00000012command=fetch
 0001000ethin-pack
 000eofs-delta
+0010no-progress
 000ddeepen 1
 0017deepen-since 12345
 0035shallow 7b333369de1221f9bfbbe03a3a13e9a09bc1c9ff