implement gix index from-tree

gitoxide-core/src/index/mod.rs

@@ -1,6 +1,6 @@
-use std::path::Path;
-
+use git::odb::FindExt;
 use git_repository as git;
+use std::path::{Path, PathBuf};
 
 pub struct Options {
     pub object_hash: git::hash::Kind,
@@ -86,3 +86,29 @@ pub fn information(
         }
     }
 }
+
+pub fn from_tree(
+    id: git::hash::ObjectId,
+    path: PathBuf,
+    force: bool,
+    repo: git::Repository,
+    mut err: impl std::io::Write,
+) -> anyhow::Result<()> {
+    let state = git::index::State::from_tree(&id, |oid, buf| repo.objects.find_tree_iter(oid, buf).ok())?;
+
+    if path.is_file() {
+        writeln!(err, "File {:?} already exists", path).ok();
+        if force {
+            writeln!(err, "overwriting").ok();
+        } else {
+            anyhow::bail!("exiting");
+        }
+    }
+
+    let mut file = std::fs::File::create(&path)?;
+    state.write_to(&mut file, git::index::write::Options::default())?;
+
+    writeln!(err, "Successfully wrote file {:?}", path).ok();
+
+    Ok(())
+}

src/plumbing/main.rs

@@ -15,7 +15,7 @@ use gitoxide_core::pack::verify;
 
 use crate::{
     plumbing::options::{
-        commit, config, credential, exclude, free, mailmap, odb, remote, revision, tree, Args, Subcommands,
+        commit, config, credential, exclude, free, index, mailmap, odb, remote, revision, tree, Args, Subcommands,
     },
     shared::pretty::prepare_and_run,
 };
@@ -755,6 +755,16 @@ pub fn main() -> Result<()> {
                 },
             ),
         },
+        Subcommands::Index(cmd) => match cmd {
+            index::Subcommands::FromTree { force, id, path } => prepare_and_run(
+                "index-read-tree",
+                verbose,
+                progress,
+                progress_keep_open,
+                None,
+                move |_progress, _out, err| core::index::from_tree(id, path, force, repository(Mode::Strict)?, err),
+            ),
+        },
     }?;
     Ok(())
 }

src/plumbing/options.rs

@@ -1,8 +1,7 @@
-use std::path::PathBuf;
-
 use git_repository as git;
 use git_repository::bstr::BString;
 use gitoxide_core as core;
+use std::path::PathBuf;
 
 #[derive(Debug, clap::Parser)]
 #[clap(name = "gix-plumbing", about = "The git underworld", version = clap::crate_version!())]
@@ -93,6 +92,9 @@ pub enum Subcommands {
     /// Subcommands that need no git repository to run.
     #[clap(subcommand)]
     Free(free::Subcommands),
+    /// Interact with index files
+    #[clap(subcommand)]
+    Index(index::Subcommands),
 }
 
 pub mod config {
@@ -304,6 +306,7 @@ pub mod free {
         }
     }
 
+    ///
     pub mod index {
         use std::path::PathBuf;
 
@@ -664,3 +667,21 @@ pub mod exclude {
         },
     }
 }
+
+pub mod index {
+    use std::path::PathBuf;
+
+    #[derive(Debug, clap::Subcommand)]
+    pub enum Subcommands {
+        #[clap(visible_alias = "read-tree")]
+        FromTree {
+            /// Overwrite the specified file if it already exists
+            #[clap(long, short = 'f')]
+            force: bool,
+            /// Hash of the tree object to generate the index from
+            id: git_repository::hash::ObjectId,
+            /// Path to the index file to be written
+            path: PathBuf,
+        },
+    }
+}