remove all old format (tar/container) support

[cgwalters]

Let's do this alongside the next semver break in 0.9.

[cgwalters]

OK and when we do this, we can convert the main tar export path to be identical to a single-layer chunked container image. This will drop a lot of duplicate code in the tar export path.
(The cost though is we'll need to build up a mapping of the content objects in checksum order instead of directory order in that case too, but eh)

[cgwalters]

Started on this

commit 7fa1c40f5c2b65071dec73917bd5c8be0ac5b9a4
Author:     Colin Walters <walters@verbum.org>
AuthorDate: Tue Jun 28 13:36:33 2022 -0400
Commit:     Colin Walters <walters@verbum.org>
CommitDate: Tue Jun 28 13:36:33 2022 -0400

    tar: Always export metadata first, then content objects

diff --git a/lib/src/tar/export.rs b/lib/src/tar/export.rs
index f7180d9..bcb1205 100644
--- a/lib/src/tar/export.rs
+++ b/lib/src/tar/export.rs
@@ -70,8 +70,6 @@ struct OstreeTarWriter<'a, W: std::io::Write> {
     out: &'a mut tar::Builder<W>,
     options: ExportOptions,
     wrote_initdirs: bool,
-    /// True if we're only writing directories
-    structure_only: bool,
     wrote_dirtree: HashSet<String>,
     wrote_dirmeta: HashSet<String>,
     wrote_content: HashSet<String>,
@@ -155,7 +153,6 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
             out,
             options,
             wrote_initdirs: false,
-            structure_only: false,
             wrote_dirmeta: HashSet::new(),
             wrote_dirtree: HashSet::new(),
             wrote_content: HashSet::new(),
@@ -266,7 +263,7 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
     }
 
     /// Recursively serialize a commit object to the target tar stream.
-    fn write_commit(&mut self) -> Result<()> {
+    fn write_metadata(&mut self) -> Result<()> {
         let cancellable = gio::NONE_CANCELLABLE;
 
         let commit_bytes = self.commit_object.data_as_bytes();
@@ -299,11 +296,30 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
             Utf8Path::new(TAR_PATH_PREFIX_V0),
             contents,
             true,
+            true,
             cancellable,
         )?;
         Ok(())
     }
 
+    fn write_contents(&mut self) -> Result<()> {
+        let cancellable = gio::NONE_CANCELLABLE;
+        let commit_bytes = self.commit_object.data_as_bytes();
+        let commit_bytes = commit_bytes.try_as_aligned()?;
+        let commit = gv_commit!().cast(commit_bytes);
+        let commit = commit.to_tuple();
+        let contents = hex::encode(commit.6);
+
+        // Recurse and write everything else.
+        self.append_dirtree(
+            Utf8Path::new(TAR_PATH_PREFIX_V0),
+            contents,
+            true,
+            false,
+            cancellable,
+        )
+    }
+
     fn append_commit_object(&mut self) -> Result<()> {
         self.append(
             ostree::ObjectType::Commit,
@@ -493,6 +509,7 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
         dirpath: &Utf8Path,
         checksum: String,
         is_root: bool,
+        metadata_only: bool,
         cancellable: Option<&C>,
     ) -> Result<()> {
         let v = &self
@@ -509,7 +526,7 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
             c.set_error_if_cancelled()?;
         }
 
-        if !self.structure_only {
+        if !metadata_only {
             for file in files {
                 let (name, csum) = file.to_tuple();
                 let name = name.to_str();
@@ -529,7 +546,9 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
                 let meta_v = &self
                     .repo
                     .load_variant(ostree::ObjectType::DirMeta, meta_csum)?;
-                self.append(ostree::ObjectType::DirMeta, meta_csum, meta_v)?;
+                if metadata_only {
+                    self.append(ostree::ObjectType::DirMeta, meta_csum, meta_v)?;
+                }
                 // Safety: We passed the correct variant type just above
                 ostree::DirMetaParsed::from_variant(meta_v).unwrap()
             };
@@ -540,8 +559,10 @@ impl<'a, W: std::io::Write> OstreeTarWriter<'a, W> {
             let dirtree_csum = hex::encode(contents_csum);
             let subpath = &dirpath.join(name);
             let subpath = map_path(subpath);
-            self.append_dir(&*subpath, &metadata)?;
-            self.append_dirtree(&*subpath, dirtree_csum, false, cancellable)?;
+            if metadata_only {
+                self.append_dir(&*subpath, &metadata)?;
+            }
+            self.append_dirtree(&*subpath, dirtree_csum, false, metadata_only, cancellable)?;
         }
 
         Ok(())
@@ -559,7 +580,8 @@ fn impl_export<W: std::io::Write>(
     options: ExportOptions,
 ) -> Result<()> {
     let writer = &mut OstreeTarWriter::new(repo, commit_checksum, out, options)?;
-    writer.write_commit()?;
+    writer.write_metadata()?;
+    writer.write_contents()?;
     Ok(())
 }
 
@@ -636,11 +658,7 @@ pub(crate) fn export_final_chunk<W: std::io::Write>(
         ..Default::default()
     };
     let writer = &mut OstreeTarWriter::new(repo, commit_checksum, out, options)?;
-    // For the final chunk, output the commit object, plus all ostree metadata objects along with
-    // the containing directories.
-    writer.structure_only = true;
-    writer.write_commit()?;
-    writer.structure_only = false;
+    writer.write_metadata()?;
     write_chunk(writer, remainder.content)
 }
 

[cgwalters]

OK fully pulling off the bandaid here would be a big move. Let's try to be a bit more incremental; did that in #378

[cgwalters]

If everything goes well after shipping 0.9, let's do this in 0.10.