Assure short ids are not ambiguous

It's actually quite involved to get proper short-ids, and git even
applies some heuristics to calculate good starting values for
the abbreviation length, right before validating uniqueness.

Author: Byron

src/info/head_refs.rs

@@ -1,31 +1,32 @@
-use git_repository as git;
 use serde::ser::SerializeStruct;
 use serde::Serialize;
 
 pub struct HeadRefs {
-    commit: git::hash::ObjectId,
+    short_commit_id: String,
     refs: Vec<String>,
 }
 
 impl HeadRefs {
-    pub fn new(commit: git::hash::ObjectId, refs: Vec<String>) -> HeadRefs {
-        HeadRefs { commit, refs }
+    pub fn new(short_commit_id: String, refs: Vec<String>) -> HeadRefs {
+        HeadRefs {
+            short_commit_id,
+            refs,
+        }
     }
 }
 
 impl std::fmt::Display for HeadRefs {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        let short_commit = self.commit.to_string().chars().take(7).collect::<String>();
         if !self.refs.is_empty() {
             let refs_str = self
                 .refs
                 .iter()
                 .map(|ref_name| ref_name.as_str())
                 .collect::<Vec<&str>>()
                 .join(", ");
-            write!(f, "{} ({})", short_commit, refs_str)
+            write!(f, "{} ({})", self.short_commit_id, refs_str)
         } else {
-            write!(f, "{}", short_commit)
+            write!(f, "{}", self.short_commit_id)
         }
     }
 }
@@ -37,10 +38,7 @@ impl Serialize for HeadRefs {
     {
         let mut state = serializer.serialize_struct("HeadRefs", 2)?;
         state.serialize_field("refs", &self.refs)?;
-        state.serialize_field(
-            "oid",
-            &self.commit.to_string().chars().take(7).collect::<String>(),
-        )?;
+        state.serialize_field("oid", &self.short_commit_id)?;
         state.end()
     }
 }

src/info/repo.rs

@@ -304,9 +304,9 @@ impl<'a> Repo<'a> {
         let head_oid = self
             .repo
             .head()
-            .with_context(|| "Could not read HEAD")?
-            .peel_to_commit_in_place()?
-            .id;
+            .context("Could not read HEAD")?
+            .peel_to_id_in_place()
+            .context("The repository isn't initialized")??;
         let refs_info = self
             .repo
             .references()?
@@ -319,7 +319,7 @@ impl<'a> Repo<'a> {
                 .then(|| reference.name().shorten().to_string())
             })
             .collect();
-        Ok(HeadRefs::new(head_oid, refs_info))
+        Ok(HeadRefs::new(head_oid.shorten()?.to_string(), refs_info))
     }
 
     fn work_dir(&self) -> Result<&Path> {