fetchTree/fetchGit: re-enable shallow fetching

Add several tests for git fetching:
- shallow-cache-separation: can fetch the same repo shallowly and non-shallowly
- shallow-ignore-ref: ensure that ref gets ignored when shallow=true is set
- ssh-shallow: can fetch a git repo via ssh using shallow=1

tests/nixos/fetch-git/test-cases/shallow-cache-separation/default.nix

@@ -0,0 +1,57 @@
+{
+  description = "can fetch the same repo shallowly and non-shallowly";
+  script = ''
+    # create branch1 off of main
+    client.succeed(f"""
+      echo chiang-mai > {repo.path}/thailand \
+      && {repo.git} add thailand \
+      && {repo.git} commit -m 'commit1' \
+      \
+      && {repo.git} push origin --all
+    """)
+
+    # save the revision
+    mainRev = client.succeed(f"""
+      {repo.git} rev-parse main
+    """).strip()
+
+    # fetch shallowly
+    revCountShallow = client.succeed(f"""
+      nix eval --impure --expr '
+        (builtins.fetchGit {{
+          url = "{repo.remote}";
+          rev = "{mainRev}";
+          shallow = true;
+        }}).revCount
+      '
+    """).strip()
+    # ensure the revCount is 0
+    assert revCountShallow == "0", f"revCountShallow should be 0, but is {revCountShallow}"
+
+    # fetch non-shallowly
+    revCountNonShallow = client.succeed(f"""
+      nix eval --impure --expr '
+        (builtins.fetchGit {{
+          url = "{repo.remote}";
+          rev = "{mainRev}";
+          shallow = false;
+        }}).revCount
+      '
+    """).strip()
+    # ensure the revCount is 1
+    assert revCountNonShallow == "1", f"revCountNonShallow should be 1, but is {revCountNonShallow}"
+
+    # fetch shallowly again
+    revCountShallow2 = client.succeed(f"""
+      nix eval --impure --expr '
+        (builtins.fetchGit {{
+          url = "{repo.remote}";
+          rev = "{mainRev}";
+          shallow = true;
+        }}).revCount
+      '
+    """).strip()
+    # ensure the revCount is 0
+    assert revCountShallow2 == "0", f"revCountShallow2 should be 0, but is {revCountShallow2}"
+  '';
+}

tests/nixos/fetch-git/test-cases/shallow-ignore-ref/default.nix

@@ -0,0 +1,40 @@
+{
+  description = "ensure that ref gets ignored when shallow=true is set";
+  script = ''
+    # create branch1 off of main
+    client.succeed(f"""
+      echo chiang-mai > {repo.path}/thailand \
+      && {repo.git} add thailand \
+      && {repo.git} commit -m 'commit1' \
+      \
+      && {repo.git} checkout -b branch1 main \
+      && echo bangkok > {repo.path}/thailand \
+      && {repo.git} add thailand \
+      && {repo.git} commit -m 'commit2' \
+      \
+      && {repo.git} push origin --all
+    """)
+
+    # save the revisions
+    mainRev = client.succeed(f"""
+      {repo.git} rev-parse main
+    """).strip()
+    branch1Rev = client.succeed(f"""
+      {repo.git} rev-parse branch1
+    """).strip()
+
+    # Ensure that ref gets ignored when fetching shallowly.
+    # This would fail if the ref was respected, as branch1Rev is not on main.
+    client.succeed(f"""
+      nix eval --impure --raw --expr '
+        (builtins.fetchGit {{
+          url = "{repo.remote}";
+          rev = "{branch1Rev}";
+          ref = "main";
+          shallow = true;
+        }})
+      '
+    """)
+
+  '';
+}

tests/nixos/fetch-git/test-cases/ssh-shallow/default.nix

@@ -0,0 +1,52 @@
+{
+  description = "can fetch a git repo via ssh using shallow=1";
+  script = ''
+    # add a file to the repo
+    client.succeed(f"""
+      echo chiang-mai > {repo.path}/thailand \
+      && {repo.git} add thailand \
+      && {repo.git} commit -m 'commit1'
+    """)
+
+    # memoize the revision
+    rev1 = client.succeed(f"""
+      {repo.git} rev-parse HEAD
+    """).strip()
+
+    # push to the server
+    client.succeed(f"""
+      {repo.git} push origin-ssh main
+    """)
+
+    fetchGit_expr = f"""
+      builtins.fetchGit {{
+        url = "{repo.remote_ssh}";
+        rev = "{rev1}";
+        shallow = true;
+      }}
+    """
+
+    # fetch the repo via nix
+    fetched1 = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_expr}).outPath'
+    """)
+
+    # check if the committed file is there
+    client.succeed(f"""
+      test -f {fetched1}/thailand
+    """)
+
+    # check if the revision is the same
+    rev1_fetched = client.succeed(f"""
+      nix eval --impure --raw --expr '({fetchGit_expr}).rev'
+    """).strip()
+    assert rev1 == rev1_fetched, f"rev1: {rev1} != rev1_fetched: {rev1_fetched}"
+
+    # check if revCount is 1
+    revCount1 = client.succeed(f"""
+      nix eval --impure --expr '({fetchGit_expr}).revCount'
+    """).strip()
+    print(f"revCount1: {revCount1}")
+    assert revCount1 == '0', f"rev count is not 0 but {revCount1}"
+  '';
+}

tests/nixos/fetch-git/testsupport/gitea-repo.nix

@@ -72,4 +72,4 @@ in
           """)
     '';
   };
-}
+}