add TODOs for setting git pretty_ref to url encoding

To make things more consistent, we will change to `pretty_ref(true)`
when we are going to stabilize lockfile v4.

src/cargo/core/source/source_id.rs

@@ -575,6 +575,9 @@ impl fmt::Display for SourceId {
                 // Don't replace the URL display for git references,
                 // because those are kind of expected to be URLs.
                 write!(f, "{}", self.inner.url)?;
+                // TODO(-Znext-lockfile-bump): set it to true when stabilizing
+                // lockfile v4, because we want Source ID serialization to be
+                // consistent with lockfile.
                 if let Some(pretty) = reference.pretty_ref(false) {
                     write!(f, "?{}", pretty)?;
                 }

src/cargo/sources/git/source.rs

@@ -164,6 +164,9 @@ impl<'cfg> Debug for GitSource<'cfg> {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         write!(f, "git repo at {}", self.remote.url())?;
 
+        // TODO(-Znext-lockfile-bump): set it to true when stabilizing
+        // lockfile v4, because we want Source ID serialization to be
+        // consistent with lockfile.
         match self.manifest_reference.pretty_ref(false) {
             Some(s) => write!(f, " ({})", s),
             None => Ok(()),

src/cargo/util/toml_mut/dependency.rs

@@ -881,6 +881,10 @@ impl GitSource {
 impl std::fmt::Display for GitSource {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let git_ref = self.git_ref();
+
+        // TODO(-Znext-lockfile-bump): set it to true when stabilizing
+        // lockfile v4, because we want Source ID serialization to be
+        // consistent with lockfile.
         if let Some(pretty_ref) = git_ref.pretty_ref(false) {
             write!(f, "{}?{}", self.git, pretty_ref)
         } else {