3 files changed, 54 insertions, 20 deletions
diff --git a/app/assets/javascripts/diffs/store/actions.js b/app/assets/javascripts/diffs/store/actions.js
index c87e178c8cf..c0456c18e44 100644
--- a/app/assets/javascripts/diffs/store/actions.js
+++ b/app/assets/javascripts/diffs/store/actions.js
@@ -147,13 +147,19 @@ export const scrollToLineIfNeededParallel = (_, line) => {
   }
 };
 
-export const loadCollapsedDiff = ({ commit }, file) =>
-  axios.get(file.load_collapsed_diff_url).then(res => {
-    commit(types.ADD_COLLAPSED_DIFFS, {
-      file,
-      data: res.data,
+export const loadCollapsedDiff = ({ commit, getters }, file) =>
+  axios
+    .get(file.load_collapsed_diff_url, {
+      params: {
+        commit_id: getters.commitId,
+      },
+    })
+    .then(res => {
+      commit(types.ADD_COLLAPSED_DIFFS, {
+        file,
+        data: res.data,
+      });
     });
-  });
 
 export const expandAllFiles = ({ commit }) => {
   commit(types.EXPAND_ALL_FILES);
diff --git a/changelogs/unreleased/diff-expand-commit-file.yml b/changelogs/unreleased/diff-expand-commit-file.yml
new file mode 100644
index 00000000000..8ca784d75c1
--- /dev/null
+++ b/changelogs/unreleased/diff-expand-commit-file.yml
@@ -0,0 +1,5 @@
+---
+title: Fixed diff files expanding not loading commit content
+merge_request:
+author:
+type: fixed
diff --git a/spec/javascripts/diffs/store/actions_spec.js b/spec/javascripts/diffs/store/actions_spec.js
index 5656ce16db0..4b339a0553f 100644
--- a/spec/javascripts/diffs/store/actions_spec.js
+++ b/spec/javascripts/diffs/store/actions_spec.js
@@ -382,24 +382,47 @@ describe('DiffsStoreActions', () => {
       const file = { hash: 123, load_collapsed_diff_url: '/load/collapsed/diff/url' };
       const data = { hash: 123, parallelDiffLines: [{ lineCode: 1 }] };
       const mock = new MockAdapter(axios);
+      const commit = jasmine.createSpy('commit');
       mock.onGet(file.loadCollapsedDiffUrl).reply(200, data);
 
-      testAction(
-        loadCollapsedDiff,
-        file,
-        {},
-        [
-          {
-            type: types.ADD_COLLAPSED_DIFFS,
-            payload: { file, data },
-          },
-        ],
-        [],
-        () => {
+      loadCollapsedDiff({ commit, getters: { commitId: null } }, file)
+        .then(() => {
+          expect(commit).toHaveBeenCalledWith(types.ADD_COLLAPSED_DIFFS, { file, data });
+
           mock.restore();
           done();
-        },
-      );
+        })
+        .catch(done.fail);
+    });
+
+    it('should fetch data without commit ID', () => {
+      const file = { load_collapsed_diff_url: '/load/collapsed/diff/url' };
+      const getters = {
+        commitId: null,
+      };
+
+      spyOn(axios, 'get').and.returnValue(Promise.resolve({ data: {} }));
+
+      loadCollapsedDiff({ commit() {}, getters }, file);
+
+      expect(axios.get).toHaveBeenCalledWith(file.load_collapsed_diff_url, {
+        params: { commit_id: null },
+      });
+    });
+
+    it('should fetch data with commit ID', () => {
+      const file = { load_collapsed_diff_url: '/load/collapsed/diff/url' };
+      const getters = {
+        commitId: '123',
+      };
+
+      spyOn(axios, 'get').and.returnValue(Promise.resolve({ data: {} }));
+
+      loadCollapsedDiff({ commit() {}, getters }, file);
+
+      expect(axios.get).toHaveBeenCalledWith(file.load_collapsed_diff_url, {
+        params: { commit_id: '123' },
+      });
     });
   });