cli: consistently check that a commit can be rewritten before rewriting it

This patch adds checks in all (?) commands that rewrite commits to
make sure the commit they're about to rewrite is allowed to be
rewritten. The only check we do is that it's not a root commit. We
should at least add checks for public commits later.

src/commands.rs

@@ -268,6 +268,15 @@ impl RepoCommandHelper {
         Ok(revset::parse(revision_str)?)
     }
 
+    fn check_rewriteable(&self, commit: &Commit) -> Result<(), CommandError> {
+        if commit.id() == self.repo.store().root_commit_id() {
+            return Err(CommandError::UserError(String::from(
+                "Cannot rewrite the root commit",
+            )));
+        }
+        Ok(())
+    }
+
     fn commit_working_copy(&mut self) -> Commit {
         let (reloaded_repo, commit) = self
             .repo
@@ -1389,6 +1398,7 @@ fn cmd_describe(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let description;
     if sub_matches.is_present("stdin") {
@@ -1415,6 +1425,7 @@ fn cmd_open(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let mut tx = repo_command.start_transaction(&format!("open commit {}", commit.id().hex()));
     CommitBuilder::for_rewrite_from(ui.settings(), repo.store(), &commit)
@@ -1431,6 +1442,7 @@ fn cmd_close(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let mut commit_builder =
         CommitBuilder::for_rewrite_from(ui.settings(), repo.store(), &commit).set_open(false);
@@ -1477,12 +1489,8 @@ fn cmd_prune(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let predecessor = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&predecessor)?;
     let repo = repo_command.repo();
-    if predecessor.id() == repo.store().root_commit_id() {
-        return Err(CommandError::UserError(String::from(
-            "Cannot prune the root commit",
-        )));
-    }
     let mut tx =
         repo_command.start_transaction(&format!("prune commit {}", predecessor.id().hex()));
     CommitBuilder::for_rewrite_from(ui.settings(), repo.store(), &predecessor)
@@ -1523,6 +1531,7 @@ fn cmd_squash(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let parents = commit.parents();
     if parents.len() != 1 {
@@ -1531,11 +1540,7 @@ fn cmd_squash(
         )));
     }
     let parent = &parents[0];
-    if parent.id() == repo.store().root_commit_id() {
+    repo_command.check_rewriteable(parent)?;
-        return Err(CommandError::UserError(String::from(
-            "Cannot squash into the root commit",
-        )));
-    }
     let mut tx = repo_command.start_transaction(&format!("squash commit {}", commit.id().hex()));
     let mut_repo = tx.mut_repo();
     let new_parent_tree_id;
@@ -1585,6 +1590,7 @@ fn cmd_unsquash(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let parents = commit.parents();
     if parents.len() != 1 {
@@ -1593,11 +1599,7 @@ fn cmd_unsquash(
         )));
     }
     let parent = &parents[0];
-    if parent.id() == repo.store().root_commit_id() {
+    repo_command.check_rewriteable(&parent)?;
-        return Err(CommandError::UserError(String::from(
-            "Cannot unsquash from the root commit",
-        )));
-    }
     let mut tx = repo_command.start_transaction(&format!("unsquash commit {}", commit.id().hex()));
     let mut_repo = tx.mut_repo();
     let parent_base_tree = merge_commit_trees(repo.as_repo_ref(), &parent.parents());
@@ -1667,6 +1669,7 @@ fn cmd_restore(
     let mut repo_command = command.repo_helper(ui)?;
     let from_commit = repo_command.resolve_single_rev(sub_matches.value_of("from").unwrap())?;
     let to_commit = repo_command.resolve_single_rev(sub_matches.value_of("to").unwrap())?;
+    repo_command.check_rewriteable(&to_commit)?;
     let repo = repo_command.repo();
     let tree_id;
     if sub_matches.is_present("interactive") {
@@ -1732,6 +1735,7 @@ fn cmd_edit(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let base_tree = merge_commit_trees(repo.as_repo_ref(), &commit.parents());
     let instructions = format!(
@@ -1767,6 +1771,7 @@ fn cmd_split(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit)?;
     let repo = repo_command.repo();
     let base_tree = merge_commit_trees(repo.as_repo_ref(), &commit.parents());
     let instructions = format!(
@@ -1863,6 +1868,7 @@ fn cmd_rebase(
 ) -> Result<(), CommandError> {
     let mut repo_command = command.repo_helper(ui)?;
     let commit_to_rebase = repo_command.resolve_revision_arg(sub_matches)?;
+    repo_command.check_rewriteable(&commit_to_rebase)?;
     let mut parents = vec![];
     for revision_str in sub_matches.values_of("destination").unwrap() {
         let destination = repo_command.resolve_single_rev(revision_str)?;