fix(oca-gen-addon-readme): reduce unneeded merge conflicts

As seen in OCA#190 (comment), when somebody tried to merge 2 PRs for the same module, chances are that both imply different readme digests and the merge fails.

As seen in OCA#220 (comment), this was already happening under some circumstances with `requirements.txt` files.

Here I added a `.gitattributes` file which specifies a `merge=union` driver for those files. [Git docs][1] explain that this driver will just keep the changes from all files, marking the merge as succeeded and not including merge markers. This is not ideal, but is OK for our current situation because:

1. Duplicate/conflicting lines in those files should not really harm a lot.
2. The bot will re-render the README upon merge anyways, fixing that conflict automatically.
3. We could define a custom merge driver, but `union` is built into Git, meaning less configurations required downstream.

Still, it doesn't seem to work in octopus merges. At least, if you do consecutive merges instead, all will work as expected.

At the same time, I moved the hook to be the last. This is because previous hooks can reformat the files used to obtain the digest.

Closes OCA#220.

[1]: https://git-scm.com/docs/gitattributes.html#Documentation/gitattributes.txt-union

src/.gitattributes

@@ -0,0 +1,3 @@
+*/README.rst merge=union
+*/static/description/index.html merge=union
+requirements.txt merge=union

src/.pre-commit-config.yaml.jinja

@@ -107,20 +107,14 @@ repos:
     hooks:
       - id: whool-init
   {%- endif %}
-  - repo: https://github.com/oca/maintainer-tools
+  - &maintainer_tools
+    repo: https://github.com/oca/maintainer-tools
     rev: {{ repo_rev.maintainer_tools }}
     hooks:
       # update the NOT INSTALLABLE ADDONS section above
       - id: oca-update-pre-commit-excluded-addons
       - id: oca-fix-manifest-website
         args: ["{{ repo_website }}"]
-      - id: oca-gen-addon-readme
-        args:
-          - --addons-dir=.
-          - --branch={{ "%.01f" | format(odoo_version) }}
-          - --org-name={{ org_slug }}
-          - --repo-name={{ repo_slug }}
-          - --if-source-changed
       {%- if use_pyproject_toml and generate_requirements_txt %}
       - id: oca-gen-external-dependencies
       {%- endif %}
@@ -245,4 +239,13 @@ repos:
       - id: pylint_odoo
         args:
           - --rcfile=.pylintrc-mandatory
+  - <<: *maintainer_tools
+    hooks:
+      - id: oca-gen-addon-readme
+        args:
+          - --addons-dir=.
+          - --branch={{ "%.01f" | format(odoo_version) }}
+          - --org-name={{ org_slug }}
+          - --repo-name={{ repo_slug }}
+          - --if-source-changed
 {%- endif %}

tests/test_pre_commit.py

@@ -1,5 +1,7 @@
+import re
 from pathlib import Path
 
+import pytest
 from copier import run_copy
 from plumbum import local
 from plumbum.cmd import git, pre_commit
@@ -17,3 +19,99 @@ def test_hooks_installable(tmp_path: Path, odoo_version: float, cloned_template:
     with local.cwd(tmp_path):
         git("init")
         pre_commit("install-hooks")
+
+
+def test_no_readme_generator_conflicts(
+    tmp_path: Path, cloned_template: Path, odoo_version: Path
+):
+    """Test that you can merge more than one PR targeting the same module."""
+    if odoo_version < 14.0:
+        pytest.skip("Older versions don't generate READMEs")
+    # Generate a repo
+    data = {
+        "odoo_version": odoo_version,
+        "repo_slug": "oca-addons-repo-template",
+        "repo_name": "Test repo",
+        "repo_description": "Test repo description",
+    }
+    run_copy(str(cloned_template), tmp_path, data=data, defaults=True, unsafe=True)
+    with local.cwd(tmp_path):
+        git("init")
+        git("checkout", "-b", odoo_version)
+        pre_commit("install")
+        git("add", "-A")
+        git("commit", "-m", "[BUILD] hello world", retcode=1)
+        git("commit", "-am", "[BUILD] hello world")
+        # Create a module
+        Path("useless_module").mkdir()
+        with local.cwd("useless_module"):
+            Path("__init__.py").touch()
+            Path("README.rst").touch()
+            Path("__manifest__.py").write_text(
+                repr(
+                    {
+                        "name": "Useless module",
+                        "version": f"{odoo_version}.0.1.0",
+                        "author": "Odoo Community Association (OCA)",
+                        "summary": "A module that does nothing.",
+                        "license": "LGPL-3",
+                        "website": "https://github.com/OCA/oca-addons-repo-template",
+                    }
+                )
+            )
+            Path("readme").mkdir()
+            Path("readme", "DESCRIPTION.md").write_text(
+                "This module is absurdly useless.\n"
+            )
+            # Commit it and let pre-commit reformat it
+            git("add", "-A")
+            git("commit", "-m", "[ADD] useless_module", retcode=1)
+            git("add", "-A")
+            git("commit", "-m", "[ADD] useless_module")
+            # At this point, the README contains the dir hash
+            orig_digest = re.search(
+                r"source digest: (.*)", Path("README.rst").read_text()
+            ).group(1)
+            assert orig_digest
+            assert Path("static", "description", "index.html").is_file()
+            # Change the module, and thus the digest in two different branches
+            git("checkout", "-b", "change1")
+            Path("readme", "USAGE.md").write_text("You cannot use this.\n")
+            git("add", "-A")
+            git("commit", "-m", "[IMP] useless_module: Usage", retcode=1)
+            git("commit", "-am", "[IMP] useless_module: Usage")
+            chg1_digest = re.search(
+                r"source digest: (.*)", Path("README.rst").read_text()
+            ).group(1)
+            assert chg1_digest
+            git("checkout", odoo_version)
+            git("checkout", "-b", "change2")
+            Path("readme", "CONFIGURE.md").write_text("You cannot configure this.\n")
+            git("add", "-A")
+            git("commit", "-m", "[IMP] useless_module: Configuration", retcode=1)
+            git("commit", "-am", "[IMP] useless_module: Configuration")
+            chg2_digest = re.search(
+                r"source digest: (.*)", Path("README.rst").read_text()
+            ).group(1)
+            assert chg2_digest
+            assert orig_digest != chg1_digest != chg2_digest
+            git("checkout", odoo_version)
+            # Merge the two branches and check there are no conflicts
+            git("merge", "change1")
+            assert f"source digest: {orig_digest}" not in Path("README.rst").read_text()
+            assert f"source digest: {chg1_digest}" in Path("README.rst").read_text()
+            assert f"source digest: {chg2_digest}" not in Path("README.rst").read_text()
+            git("merge", "change2")
+            assert f"source digest: {orig_digest}" not in Path("README.rst").read_text()
+            assert f"source digest: {chg1_digest}" in Path("README.rst").read_text()
+            assert f"source digest: {chg2_digest}" in Path("README.rst").read_text()
+            # Pre-commit can still fix the README
+            assert not git("status", "--porcelain=v1")
+            pre_commit("run", "-a", retcode=1)
+            assert git("status", "--porcelain=v1") == (
+                " M useless_module/README.rst\n"
+                " M useless_module/static/description/index.html\n"
+            )
+            assert f"source digest: {orig_digest}" not in Path("README.rst").read_text()
+            assert f"source digest: {chg1_digest}" not in Path("README.rst").read_text()
+            assert f"source digest: {chg2_digest}" not in Path("README.rst").read_text()