path_slash

cli/Cargo.toml

@@ -74,6 +74,7 @@ jj-lib = { workspace = true }
 maplit = { workspace = true }
 minus = { workspace = true }
 once_cell = { workspace = true }
+path-slash = "0.2.1"
 pest = { workspace = true }
 pest_derive = { workspace = true }
 pollster = { workspace = true }

cli/src/commands/git/clone.rs

@@ -20,6 +20,7 @@ use jj_lib::git::{self, GitFetchError, GitFetchStats};
 use jj_lib::repo::Repo;
 use jj_lib::str_util::StringPattern;
 use jj_lib::workspace::Workspace;
+use path_slash::PathBufExt;
 
 use crate::cli_util::{CommandHelper, WorkspaceCommandHelper};
 use crate::command_error::{cli_error, user_error, user_error_with_message, CommandError};
@@ -55,10 +56,12 @@ fn absolute_git_source(cwd: &Path, source: &str) -> String {
     // drive letter.
     if !source.contains(':') && Path::new(source).exists() {
         // It's less likely that cwd isn't utf-8, so just fall back to original source.
+        // TODO: This won't work for Windows UNC path or (less importantly) if the
+        // original source is a non-UTF Windows path. For Windows UNC paths, we
+        // could use dunce, though see also https://gitlab.com/kornelski/dunce/-/issues/7
         cwd.join(source)
-            .into_os_string()
-            .into_string()
-            .unwrap_or_else(|_| source.to_owned())
+            .to_slash()
+            .map_or_else(|| source.to_owned(), |s| s.to_string())
     } else {
         source.to_owned()
     }