commit: Add an API to warn but continue on files in /var

xref coreos/rpm-ostree#4017

I want to have rpm-ostree use this API, but in order to do so
in a backwards compatible way we need a mode that just warns but
continues.

lib/src/commit.rs

@@ -47,10 +47,7 @@ fn process_dir_recurse(root: &Dir, path: &Utf8Path, error_count: &mut i32) -> Re
     Ok(validated)
 }
 
-/// Given a root filesystem, clean out empty directories and warn about
-/// files in /var.  /run, /tmp, and /var/tmp have their contents recursively cleaned.
-pub fn prepare_ostree_commit_in(root: &Dir) -> Result<()> {
-    let mut error_count = 0;
+fn clean_paths_in(root: &Dir) -> Result<()> {
     for path in FORCE_CLEAN_PATHS {
         if let Some(subdir) = root.open_dir_optional(path)? {
             for entry in subdir.entries()? {
@@ -59,13 +56,34 @@ pub fn prepare_ostree_commit_in(root: &Dir) -> Result<()> {
             }
         }
     }
+    Ok(())
+}
+
+fn process_var(root: &Dir, strict: bool) -> Result<()> {
     let var = Utf8Path::new("var");
+    let mut error_count = 0;
     if root.try_exists(var)? && !process_dir_recurse(root, var, &mut error_count)? {
-        anyhow::bail!("Found content in {var}");
+        if strict {
+            anyhow::bail!("Found content in {var}");
+        }
     }
     Ok(())
 }
 
+/// Given a root filesystem, clean out empty directories and warn about
+/// files in /var.  /run, /tmp, and /var/tmp have their contents recursively cleaned.
+pub fn prepare_ostree_commit_in(root: &Dir) -> Result<()> {
+    clean_paths_in(root)?;
+    process_var(root, true)
+}
+
+/// Like [`prepare_ostree_commit_in`] but only emits warnings about unsupported
+/// files in `/var` and will not error.
+pub fn prepare_ostree_commit_in_nonstrict(root: &Dir) -> Result<()> {
+    clean_paths_in(root)?;
+    process_var(root, false)
+}
+
 /// Entrypoint to the commit procedures, initially we just
 /// have one validation but we expect more in the future.
 pub(crate) async fn container_commit() -> Result<()> {
@@ -87,6 +105,7 @@ mod tests {
 
         // Handle the empty case
         prepare_ostree_commit_in(td).unwrap();
+        prepare_ostree_commit_in_nonstrict(td).unwrap();
 
         let var = Utf8Path::new("var");
         let run = Utf8Path::new("run");
@@ -119,6 +138,10 @@ mod tests {
         assert!(prepare_ostree_commit_in(td).is_err());
         assert!(td.try_exists(var)?);
 
+        td.write(var.join("foo"), "somefile")?;
+        prepare_ostree_commit_in_nonstrict(td).unwrap();
+        assert!(td.try_exists(var)?);
+
         let nested = Utf8Path::new("var/lib/nested");
         td.create_dir_all(&nested)?;
         td.write(nested.join("foo"), "test1")?;