[git] Fix switching branch of shallow clone (#18728)

* [git] Fix fetching branch of shallow clone

* Use absolute file:// paths to make sure git uses shallow clones

* Improve tests

* Fix sanity errors
* Match style according to other (depth) tests

* Improve tests

Now they will fail without the fix of this PR

lib/ansible/modules/source_control/git.py

@@ -716,8 +716,6 @@ def fetch(git_path, module, repo, dest, version, remote, depth, bare, refspec, g
                 # ensure that remote branch is available as both local and remote ref
                 refspecs.append('+refs/heads/%s:refs/heads/%s' % (version, version))
             refspecs.append('+refs/heads/%s:refs/remotes/%s/%s' % (version, remote, version))
-            else:
-                refspecs.append(version)
         elif is_remote_tag(git_path, module, dest, repo, version):
             refspecs.append('+refs/tags/' + version + ':refs/tags/' + version)
         if refspecs:

test/integration/targets/git/tasks/depth.yml

@@ -171,3 +171,54 @@
   file:
     state: absent
     path: "{{ checkout_dir }}"
+
+#
+# Make sure shallow fetch works when switching to (fetching) a new a branch
+#
+
+- name: DEPTH | clone from branch with depth specified
+  git:
+    repo: 'file://{{ repo_dir|expanduser }}/shallow_branches'
+    dest: '{{ checkout_dir }}'
+    depth: 1
+    version: test_branch
+
+- name: DEPTH | check if clone is shallow
+  stat: path={{ checkout_dir }}/.git/shallow
+  register: is_shallow
+  when: git_version.stdout is version(git_version_supporting_depth, '>=')
+
+- name: DEPTH | assert that clone is shallow
+  assert:
+    that:
+      - is_shallow.stat.exists
+  when: git_version.stdout is version(git_version_supporting_depth, '>=')
+
+- name: DEPTH | switch to new branch (fetch) with the shallow clone
+  git:
+    repo: 'file://{{ repo_dir|expanduser }}/shallow_branches'
+    dest: '{{ checkout_dir }}'
+    depth: 1
+    version: new_branch
+  register: git_fetch
+
+- name: DEPTH | assert if switching a shallow clone to a new branch worked
+  assert:
+    that:
+      - git_fetch is changed
+
+- name: DEPTH | check if clone is still shallow
+  stat: path={{ checkout_dir }}/.git/shallow
+  register: is_shallow
+  when: git_version.stdout is version(git_version_supporting_depth, '>=')
+
+- name: DEPTH | assert that clone still is shallow
+  assert:
+    that:
+      - is_shallow.stat.exists
+  when: git_version.stdout is version(git_version_supporting_depth, '>=')
+
+- name: DEPTH | clear checkout_dir
+  file:
+    state: absent
+    path: "{{ checkout_dir }}"

test/integration/targets/git/tasks/setup-local-repos.yml

@@ -5,6 +5,7 @@
   with_items:
     - "{{ repo_dir }}/minimal"
     - "{{ repo_dir }}/shallow"
+    - "{{ repo_dir }}/shallow_branches"
 
 - name: SETUP-LOCAL-REPOS | prepare minimal git repo
   shell: git init; echo "1" > a; git add a; git commit -m "1"
@@ -24,3 +25,12 @@
   register: git_shallow_head_1
   args:
     chdir: "{{ repo_dir }}/shallow"
+
+- name: prepare tmp git repo with two branches
+  shell: |
+    git init
+    echo "1" > a; git add a; git commit -m "1"
+    git checkout -b test_branch; echo "2" > a; git commit -m "2 on branch" a
+    git checkout -b new_branch; echo "3" > a; git commit -m "3 on new branch" a
+  args:
+    chdir: "{{ repo_dir }}/shallow_branches"