fix: normalize relative git submodule urls with ssh://

Git only assumes a submodule URL is a relative path if it starts with `./`
or `../` [^1]. To fetch the correct repo, we need to construct an aboslute
submodule URL.

At this moment it comes with some limitations:

* GitHub doesn't accept non-normalized URLs wth relative paths.
  (`ssh://git@github.com/rust-lang/cargo.git/relative/..` is invalid)
* `url` crate cannot parse SCP-like URLs.
  (`git@github.com:rust-lang/cargo.git` is not a valid WHATWG URL)

To overcome these, this patch always tries `Url::parse` first to normalize
the path. If it couldn't, append the relative path as the last resort and
pray the remote git service supports non-normalized URLs.

See also rust-lang/cargo#12404 and rust-lang/cargo#12295.

[^1]: <https://git-scm.com/docs/git-submodule>

src/cargo/sources/git/utils.rs

@@ -440,20 +440,7 @@ impl<'a> GitCheckout<'a> {
                 return Ok(());
             }
 
-            // Git only assumes a URL is a relative path if it starts with `./` or `../`.
+            let child_remote_url = absolute_submodule_url(parent_remote_url, child_url_str)?;
-            // See [`git submodule add`] documentation.
-            //
-            // [`git submodule add`]: https://git-scm.com/docs/git-submodule
-            let child_remote_url = if ["./", "../"].iter().any(|p| child_url_str.starts_with(p)) {
-                let mut new_remote_url = parent_remote_url.to_string();
-                if !new_remote_url.ends_with('/') {
-                    new_remote_url.push('/');
-                }
-                new_remote_url.push_str(child_url_str);
-                Cow::from(new_remote_url)
-            } else {
-                Cow::from(child_url_str)
-            };
 
             // A submodule which is listed in .gitmodules but not actually
             // checked out will not have a head id, so we should ignore it.
@@ -507,6 +494,58 @@ impl<'a> GitCheckout<'a> {
     }
 }
 
+/// Constructs an absolute URL for a child submodule URL with its parent base URL.
+///
+/// Git only assumes a submodule URL is a relative path if it starts with `./`
+/// or `../` [^1]. To fetch the correct repo, we need to construct an absolute
+/// submodule URL.
+///
+/// At this moment it comes with some limitations:
+///
+/// * GitHub doesn't accept non-normalized URLs with relative paths.
+///   (`ssh://git@github.com/rust-lang/cargo.git/relative/..` is invalid)
+/// * `url` crate cannot parse SCP-like URLs.
+///   (`git@github.com:rust-lang/cargo.git` is not a valid WHATWG URL)
+///
+/// To overcome these, this patch always tries [`Url::parse`] first to normalize
+/// the path. If it couldn't, append the relative path as the last resort and
+/// pray the remote git service supports non-normalized URLs.
+///
+/// See also rust-lang/cargo#12404 and rust-lang/cargo#12295.
+///
+/// [^1]: <https://git-scm.com/docs/git-submodule>
+fn absolute_submodule_url<'s>(base_url: &str, submodule_url: &'s str) -> CargoResult<Cow<'s, str>> {
+    let absolute_url = if ["./", "../"].iter().any(|p| submodule_url.starts_with(p)) {
+        match Url::parse(base_url) {
+            Ok(mut base_url) => {
+                let path = base_url.path();
+                if !path.ends_with('/') {
+                    base_url.set_path(&format!("{path}/"));
+                }
+                let absolute_url = base_url.join(submodule_url).with_context(|| {
+                    format!(
+                        "failed to parse relative child submodule url `{submodule_url}` \
+                        using parent base url `{base_url}`"
+                    )
+                })?;
+                Cow::from(absolute_url.to_string())
+            }
+            Err(_) => {
+                let mut absolute_url = base_url.to_string();
+                if !absolute_url.ends_with('/') {
+                    absolute_url.push('/');
+                }
+                absolute_url.push_str(submodule_url);
+                Cow::from(absolute_url)
+            }
+        }
+    } else {
+        Cow::from(submodule_url)
+    };
+
+    Ok(absolute_url)
+}
+
 /// Prepare the authentication callbacks for cloning a git repository.
 ///
 /// The main purpose of this function is to construct the "authentication
@@ -1486,3 +1525,102 @@ fn is_short_hash_of(rev: &str, oid: Oid) -> bool {
         None => false,
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::absolute_submodule_url;
+
+    #[test]
+    fn test_absolute_submodule_url() {
+        let cases = [
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "git@github.com:rust-lang/cargo.git",
+                "git@github.com:rust-lang/cargo.git",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "./",
+                "ssh://git@gitub.com/rust-lang/cargo/",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "../",
+                "ssh://git@gitub.com/rust-lang/",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "./foo",
+                "ssh://git@gitub.com/rust-lang/cargo/foo",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo/",
+                "./foo",
+                "ssh://git@gitub.com/rust-lang/cargo/foo",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo/",
+                "../foo",
+                "ssh://git@gitub.com/rust-lang/foo",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "../foo",
+                "ssh://git@gitub.com/rust-lang/foo",
+            ),
+            (
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "../foo/bar/../baz",
+                "ssh://git@gitub.com/rust-lang/foo/baz",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "ssh://git@gitub.com/rust-lang/cargo",
+                "ssh://git@gitub.com/rust-lang/cargo",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "./",
+                "git@github.com:rust-lang/cargo.git/./",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "../",
+                "git@github.com:rust-lang/cargo.git/../",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "./foo",
+                "git@github.com:rust-lang/cargo.git/./foo",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git/",
+                "./foo",
+                "git@github.com:rust-lang/cargo.git/./foo",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "../foo",
+                "git@github.com:rust-lang/cargo.git/../foo",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git/",
+                "../foo",
+                "git@github.com:rust-lang/cargo.git/../foo",
+            ),
+            (
+                "git@github.com:rust-lang/cargo.git",
+                "../foo/bar/../baz",
+                "git@github.com:rust-lang/cargo.git/../foo/bar/../baz",
+            ),
+        ];
+
+        for (base_url, submodule_url, expected) in cases {
+            let url = absolute_submodule_url(base_url, submodule_url).unwrap();
+            assert_eq!(
+                expected, url,
+                "base `{base_url}`; submodule `{submodule_url}`"
+            );
+        }
+    }
+}

tests/testsuite/git.rs

@@ -3633,7 +3633,7 @@ fn different_user_relative_submodules() {
             .file("Cargo.toml", &basic_lib_manifest("dep1"))
             .file("src/lib.rs", "")
     });
-    let _user2_git_project2 = git::new("user2/dep2", |project| {
+    let user2_git_project2 = git::new("user2/dep2", |project| {
         project
             .file("Cargo.toml", &basic_lib_manifest("dep1"))
             .file("src/lib.rs", "")
@@ -3673,14 +3673,14 @@ fn different_user_relative_submodules() {
             "\
 [UPDATING] git repository `{}`
 [UPDATING] git submodule `{}`
-[UPDATING] git submodule `{}/../dep2`
+[UPDATING] git submodule `{}`
 [COMPILING] dep1 v0.5.0 ({}#[..])
 [COMPILING] foo v0.5.0 ([CWD])
 [FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
 ",
             path2url(&user1_git_project.root()),
             path2url(&user2_git_project.root()),
-            path2url(&user2_git_project.root()),
+            path2url(&user2_git_project2.root()),
             path2url(&user1_git_project.root()),
         ))
         .run();