Add support for Fossil SCM branch names in vc.py. (#5046)

Add support for Fossil VCS in vc.py.

The prompt now shows the currently active Fossil branch, while inside a Fossil checkout.

news/vc.rst

@@ -0,0 +1,24 @@
+**Added:**
+
+* Display the current branch of Fossil VCS checkouts in the prompt,
+  similar to git and hg.
+
+**Changed:**
+
+* <news item>
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>

tests/prompt/test_vc.py

@@ -1,5 +1,7 @@
 import os
 import subprocess as sp
+import textwrap
+from typing import Dict, List
 from pathlib import Path
 from unittest.mock import Mock
 
@@ -8,7 +10,19 @@ import pytest
 from xonsh.prompt import vc
 
 # Xonsh interaction with version control systems.
-VC_BRANCH = {"git": {"master", "main"}, "hg": {"default"}}
+VC_BRANCH = {
+    "git": {"master", "main"},
+    "hg": {"default"},
+    "fossil": {"trunk"},
+}
+VC_INIT: Dict[str, List[List[str]]] = {
+    # A sequence of commands required to initialize a repository
+    "git": [["init"]],
+    "hg": [["init"]],
+    # Fossil "init" creates a central repository file with the given name,
+    # "open" creates the working directory at another, arbitrary location.
+    "fossil": [["init", "test.fossil"], ["open", "test.fossil"]]
+}
 
 
 @pytest.fixture(params=VC_BRANCH.keys())
@@ -20,28 +34,32 @@ def repo(request, tmpdir_factory):
     temp_dir = Path(tmpdir_factory.mktemp("dir"))
     os.chdir(temp_dir)
     try:
-        sp.call([vc, "init"])
+        for init_command in VC_INIT[vc]:
+            sp.call([vc] + init_command)
     except FileNotFoundError:
         pytest.skip(f"cannot find {vc} executable")
     if vc == "git":
-        git_config = temp_dir / ".git/config"
-        git_config.write_text(
-            """
-[user]
-name = me
-email = my@email.address
-[init]
-defaultBranch = main
-"""
-        )
-
-        # git needs at least one commit
-        Path("test-file").touch()
-        sp.call(["git", "add", "test-file"])
-        sp.call(["git", "commit", "-m", "test commit"])
+        _init_git_repository(temp_dir)
     return {"vc": vc, "dir": temp_dir}
 
 
+def _init_git_repository(temp_dir):
+    git_config = temp_dir / ".git/config"
+    git_config.write_text(textwrap.dedent(
+        """\
+        [user]
+        name = me
+        email = my@email.address
+        [init]
+        defaultBranch = main
+        """
+    ))
+    # git needs at least one commit
+    Path("test-file").touch()
+    sp.call(["git", "add", "test-file"])
+    sp.call(["git", "commit", "-m", "test commit"])
+
+
 @pytest.fixture
 def set_xenv(xession, monkeypatch):
     def _wrapper(path):
@@ -52,8 +70,15 @@ def set_xenv(xession, monkeypatch):
 
 
 def test_test_repo(repo):
-    test_vc_dir = repo["dir"] / ".{}".format(repo["vc"])
-    assert test_vc_dir.is_dir()
+    if repo["vc"] == "fossil":
+        # Fossil stores the check-out meta-data in a special file within the open check-out.
+        # At least one of these below must exist
+        metadata_file_names = {".fslckout", "_FOSSIL_"}  # .fslckout on Unix, _FOSSIL_ on Windows
+        existing_files = set(file.name for file in repo["dir"].iterdir())
+        assert existing_files.intersection(metadata_file_names)
+    else:
+        test_vc_dir = repo["dir"] / ".{}".format(repo["vc"])
+        assert test_vc_dir.is_dir()
     if repo["vc"] == "git":
         test_file = repo["dir"] / "test-file"
         assert test_file.exists()

xonsh/prompt/vc.py

@@ -124,6 +124,27 @@ def get_hg_branch(root=None):
     return branch
 
 
+def _run_fossil_cmd(cmd):
+    timeout = XSH.env.get("VC_BRANCH_TIMEOUT")
+    result = subprocess.check_output(cmd, stderr=subprocess.DEVNULL, timeout=timeout)
+    return result
+
+
+def get_fossil_branch():
+    """Attempts to find the current fossil branch. If this could not
+    be determined (timeout, not in a fossil checkout, etc.) then this returns None.
+    """
+    # from fossil branch --help: "fossil branch current: Print the name of the branch for the current check-out"
+    cmd = "fossil branch current".split()
+    try:
+        branch = xt.decode_bytes(_run_fossil_cmd(cmd))
+    except (subprocess.CalledProcessError, OSError):
+        branch = None
+    else:
+        branch = RE_REMOVE_ANSI.sub("", branch.splitlines()[0])
+    return branch
+
+
 _FIRST_BRANCH_TIMEOUT = True
 
 
@@ -156,7 +177,7 @@ def _vc_has(binary):
 
 def current_branch():
     """Gets the branch for a current working directory. Returns an empty string
-    if the cwd is not a repository.  This currently only works for git and hg
+    if the cwd is not a repository.  This currently only works for git, hg, and fossil
     and should be extended in the future.  If a timeout occurred, the string
     '<branch-timeout>' is returned.
     """
@@ -165,6 +186,8 @@ def current_branch():
         branch = get_git_branch()
     if not branch and _vc_has("hg"):
         branch = get_hg_branch()
+    if not branch and _vc_has("fossil"):
+        branch = get_fossil_branch()
     if isinstance(branch, subprocess.TimeoutExpired):
         branch = "<branch-timeout>"
         _first_branch_timeout_message()
@@ -234,6 +257,20 @@ def hg_dirty_working_directory():
         return None
 
 
+def fossil_dirty_working_directory():
+    """Returns whether the fossil checkout is dirty. If this could not
+    be determined (timeout, file not found, etc.) then this returns None.
+    """
+    cmd = ["fossil", "changes"]
+    try:
+        status = _run_fossil_cmd(cmd)
+    except (subprocess.CalledProcessError, OSError):
+        status = None
+    else:
+        status = bool(status)
+    return status
+
+
 def dirty_working_directory():
     """Returns a boolean as to whether there are uncommitted files in version
     control repository we are inside. If this cannot be determined, returns
@@ -244,6 +281,8 @@ def dirty_working_directory():
         dwd = git_dirty_working_directory()
     if dwd is None and _vc_has("hg"):
         dwd = hg_dirty_working_directory()
+    if dwd is None and _vc_has("fossil"):
+        dwd = fossil_dirty_working_directory()
     return dwd