Comment about unsupported merge strategies

backport.sh

@@ -19,7 +19,9 @@ then
     1: incorrect usage / this message
     2: unable to access worktree directory
     3: unable to create new branch
-    4: unable to cherry-pick commit"
+    4: unable to cherry-pick commit
+    5: headref not found
+    6: baseref not found"
   exit 1
 fi
 
@@ -46,6 +48,9 @@ export GIT_COMMITTER_NAME="$user_name"
 user_email="github-actions[bot]@users.noreply.github.com"
 export GIT_COMMITTER_EMAIL="$user_email"
 
+git cat-file -t "$headref" || exit 5
+git cat-file -t "$baseref" || exit 6
+
 echo "Find common ancestor between $baseref and $headref"
 ancref=$(git merge-base "$baseref" "$headref")
 

src/backport.ts

@@ -213,19 +213,28 @@ export class Backport {
       2: "because it was unable to create/access the git worktree directory",
       3: "because it was unable to create a new branch",
       4: "because it was unable to cherry-pick the commit(s)",
+      5: "because 1 or more of the commits are not available",
+      6: "because 1 or more of the commits are not available",
     };
     const reason = reasons[exitcode] ?? "due to an unknown script error";
+
+    const suggestion =
+      exitcode <= 4
+        ? dedent`\`\`\`bash
+                git fetch origin ${target}
+                git worktree add -d .worktree/${branchname} origin/${target}
+                cd .worktree/${branchname}
+                git checkout -b ${branchname}
+                ancref=$(git merge-base ${baseref} ${headref})
+                git cherry-pick -x $ancref..${headref}
+                \`\`\``
+        : dedent`Note that rebase and squash merges are not supported at this time.
+                For more information see https://github.com/zeebe-io/backport-action/issues/46.`;
+
     return dedent`Backport failed for \`${target}\`, ${reason}.
 
-                  Please cherry-pick the changes locally:
-                  \`\`\`bash
-                  git fetch origin ${target}
-                  git worktree add -d .worktree/${branchname} origin/${target}
-                  cd .worktree/${branchname}
-                  git checkout -b ${branchname}
-                  ancref=$(git merge-base ${baseref} ${headref})
-                  git cherry-pick -x $ancref..${headref}
-                  \`\`\``;
+                  Please cherry-pick the changes locally.
+                  ${suggestion}`;
   }
 
   private composeMessageForGitPushFailure(

src/test/backport.test.ts

@@ -52,7 +52,7 @@ describe("the backport action", () => {
           issue_number: 1347,
           body: dedent`Backport failed for \`stable/0.25\`, due to an unknown script error.
 
-                      Please cherry-pick the changes locally:
+                      Please cherry-pick the changes locally.
                       \`\`\`bash
                       git fetch origin stable/0.25
                       git worktree add -d .worktree/backport-1347-to-stable/0.25 origin/stable/0.25
@@ -65,6 +65,27 @@ describe("the backport action", () => {
       });
     });
 
+    describe("and backport.sh returns exit code 5", () => {
+      beforeEach(() => {
+        mockedExec.callBackportScript.mockResolvedValue(5);
+      });
+      it("comments on failure", async () => {
+        await backport.run();
+        expect(
+          mockedDefaultGithubWithBackportLabel.createComment
+        ).toHaveBeenCalledWith({
+          owner: "octocat",
+          repo: "Hello-World",
+          issue_number: 1347,
+          body: dedent`Backport failed for \`stable/0.25\`, because 1 or more of the commits are not available.
+
+                Please cherry-pick the changes locally.
+                Note that rebase and squash merges are not supported at this time.
+                For more information see https://github.com/zeebe-io/backport-action/issues/46.`,
+        });
+      });
+    });
+
     describe("and backport.sh returns exit code 0", () => {
       beforeEach(() => {
         mockedExec.callBackportScript.mockResolvedValue(0);

test/acceptance.test.ts

@@ -6,23 +6,31 @@ async function exec({
   command,
   args = [],
   options = { cwd: "test" },
+  quiet = true,
+  verbose = false,
 }: Command): Promise<Output> {
   const fullCommand = `${command} ${args?.join(" ")}`;
   const execution = execPromised(fullCommand, options);
-  execution.then((ps) => {
-    console.log(fullCommand);
-    if (ps.stdout) console.log(ps.stdout);
-    if (ps.stderr) console.log(ps.stderr);
-  });
-  execution.catch(console.error);
+  if (!quiet) {
+    execution.then((ps) => {
+      console.log(fullCommand);
+      if (verbose) {
+        if (ps.stdout) console.log(ps.stdout);
+        if (ps.stderr) console.log(ps.stderr);
+      }
+    });
+    if (verbose) {
+      execution.catch(console.error);
+    }
+  }
   return execution;
 }
 
 describe("given a git repository with a merged pr", () => {
-  beforeEach(async () => {
+  beforeAll(async () => {
     await exec({ command: "./setup.sh" });
 
-    // print and check the history graph
+    // check the history graph
     const { stdout } = await exec({
       command: "git log --graph --oneline --decorate",
       options: {
@@ -34,8 +42,19 @@ describe("given a git repository with a merged pr", () => {
     );
   });
 
+  describe("when backport.sh script is executed with unavailable headref", () => {
+    test("then it returns exit code 5", () => {
+      // promisedExec's error is unhandled when exit code is non-zero, use child.exec instead
+      child
+        .exec(
+          "./backport.sh test/repo abcdef123456 master^ release-1 backport-b-to-1"
+        )
+        .on("exit", (code) => expect(code).toBe(5));
+    });
+  });
+
   describe("when backport.sh script is executed", () => {
-    beforeEach(async () => {
+    beforeAll(async () => {
       await exec({
         command: "./backport.sh",
         args: [
@@ -46,6 +65,7 @@ describe("given a git repository with a merged pr", () => {
           "backport-b-to-1", // branchname (name of new backport branch)
         ],
         options: { cwd: "./" },
+        quiet: false,
       });
     });
 
@@ -82,7 +102,7 @@ describe("given a git repository with a merged pr", () => {
     });
   });
 
-  afterEach(async () => {
+  afterAll(async () => {
     await exec({ command: "./cleanup.sh" });
   });
 });
@@ -91,5 +111,7 @@ type Command = {
   command: string;
   args?: string[];
   options?: child.ExecOptions;
+  quiet?: boolean;
+  verbose?: boolean;
 };
 type Output = { stdout: string; stderr: string };

test/setup.sh

@@ -63,6 +63,9 @@ setup () {
 
     git init
 
+    echo "[commit]" >> .git/config
+    echo "	gpgsign = false" >> .git/config
+
     name="test-setup[bot]"
     export GIT_AUTHOR_NAME="$name"
     export GIT_COMMITTER_NAME="$name"