version: move to module, avoid circular imports (#39077)

8 files changed, 358 insertions, 268 deletions

diff --git a/lib/spack/spack/fetch_strategy.py b/lib/spack/spack/fetch_strategy.py
index f440ea94b7..1f99c4ce9e 100644
--- a/lib/spack/spack/fetch_strategy.py
+++ b/lib/spack/spack/fetch_strategy.py
@@ -45,6 +45,7 @@ import spack.util.git
 import spack.util.url as url_util
 import spack.util.web as web_util
 import spack.version
+import spack.version.git_ref_lookup
 from spack.util.compression import decompressor_for, extension_from_path
 from spack.util.executable import CommandNotFoundError, which
 from spack.util.string import comma_and, quote
@@ -1540,7 +1541,7 @@ def for_package_version(pkg, version=None):
                 f"Cannot fetch git version for {pkg.name}. Package has no 'git' attribute"
             )
         # Populate the version with comparisons to other commits
-        version.attach_git_lookup_from_package(pkg.name)
+        version.attach_lookup(spack.version.git_ref_lookup.GitRefLookup(pkg.name))
 
         # For GitVersion, we have no way to determine whether a ref is a branch or tag
         # Fortunately, we handle branches and tags identically, except tags are
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 4612f3aeb3..7a4117667b 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -48,6 +48,7 @@ import spack.util.path
 import spack.util.timer
 import spack.variant
 import spack.version as vn
+import spack.version.git_ref_lookup
 
 # these are from clingo.ast and bootstrapped later
 ASTType = None
@@ -2672,7 +2673,9 @@ class SpecBuilder:
         for root in self._specs.values():
             for spec in root.traverse():
                 if isinstance(spec.version, vn.GitVersion):
-                    spec.version.attach_git_lookup_from_package(spec.fullname)
+                    spec.version.attach_lookup(
+                        spack.version.git_ref_lookup.GitRefLookup(spec.fullname)
+                    )
 
         return self._specs
 
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 4a8ba6ae5b..6238bb8c65 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -88,6 +88,7 @@ import spack.util.spack_yaml as syaml
 import spack.util.string
 import spack.variant as vt
 import spack.version as vn
+import spack.version.git_ref_lookup
 
 __all__ = [
     "CompilerSpec",
@@ -4801,7 +4802,7 @@ class Spec:
             return
         for v in self.versions:
             if isinstance(v, vn.GitVersion) and v._ref_version is None:
-                v.attach_git_lookup_from_package(self.fullname)
+                v.attach_lookup(spack.version.git_ref_lookup.GitRefLookup(self.fullname))
 
 
 def parse_with_version_concrete(string: str, compiler: bool = False):
diff --git a/lib/spack/spack/version/__init__.py b/lib/spack/spack/version/__init__.py
new file mode 100644
index 0000000000..25745a94fd
--- /dev/null
+++ b/lib/spack/spack/version/__init__.py
@@ -0,0 +1,58 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+"""
+This module implements Version and version-ish objects.  These are:
+
+StandardVersion: A single version of a package.
+ClosedOpenRange: A range of versions of a package.
+VersionList: A ordered list of Version and VersionRange elements.
+
+The set of Version and ClosedOpenRange is totally ordered wiht <
+defined as Version(x) < VersionRange(Version(y), Version(x))
+if Version(x) <= Version(y).
+"""
+
+from .common import (
+    VersionChecksumError,
+    VersionError,
+    VersionLookupError,
+    infinity_versions,
+    is_git_version,
+)
+from .version_types import (
+    ClosedOpenRange,
+    GitVersion,
+    StandardVersion,
+    Version,
+    VersionList,
+    VersionRange,
+    from_string,
+    next_version,
+    prev_version,
+    ver,
+)
+
+#: This version contains all possible versions.
+any_version: VersionList = VersionList([":"])
+
+__all__ = [
+    "Version",
+    "VersionRange",
+    "ver",
+    "from_string",
+    "is_git_version",
+    "infinity_versions",
+    "prev_version",
+    "next_version",
+    "VersionList",
+    "ClosedOpenRange",
+    "StandardVersion",
+    "GitVersion",
+    "VersionError",
+    "VersionChecksumError",
+    "VersionLookupError",
+    "any_version",
+]
diff --git a/lib/spack/spack/version/common.py b/lib/spack/spack/version/common.py
new file mode 100644
index 0000000000..e26339d132
--- /dev/null
+++ b/lib/spack/spack/version/common.py
@@ -0,0 +1,37 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import re
+
+import spack.error
+
+# regex for a commit version
+COMMIT_VERSION = re.compile(r"^[a-f0-9]{40}$")
+
+# Infinity-like versions. The order in the list implies the comparison rules
+infinity_versions = ["stable", "trunk", "head", "master", "main", "develop"]
+
+iv_min_len = min(len(s) for s in infinity_versions)
+
+
+def is_git_version(string: str) -> bool:
+    return (
+        string.startswith("git.")
+        or len(string) == 40
+        and bool(COMMIT_VERSION.match(string))
+        or "=" in string[1:]
+    )
+
+
+class VersionError(spack.error.SpackError):
+    """This is raised when something is wrong with a version."""
+
+
+class VersionChecksumError(VersionError):
+    """Raised for version checksum errors."""
+
+
+class VersionLookupError(VersionError):
+    """Raised for errors looking up git commits as versions."""
diff --git a/lib/spack/spack/version/git_ref_lookup.py b/lib/spack/spack/version/git_ref_lookup.py
new file mode 100644
index 0000000000..93f1dfeba8
--- /dev/null
+++ b/lib/spack/spack/version/git_ref_lookup.py
@@ -0,0 +1,222 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import os
+import re
+from typing import Dict, Optional, Tuple
+
+from llnl.util.filesystem import mkdirp, working_dir
+
+import spack.caches
+import spack.fetch_strategy
+import spack.paths
+import spack.repo
+import spack.util.executable
+import spack.util.spack_json as sjson
+import spack.util.url
+import spack.version
+
+from .common import VersionLookupError
+from .lookup import AbstractRefLookup
+
+# regular expression for semantic versioning
+SEMVER_REGEX = re.compile(
+    ".+(?P<semver>([0-9]+)[.]([0-9]+)[.]([0-9]+)"
+    "(?:-([0-9A-Za-z-]+(?:[.][0-9A-Za-z-]+)*))?"
+    "(?:[+][0-9A-Za-z-]+)?)"
+)
+
+
+class GitRefLookup(AbstractRefLookup):
+    """An object for cached lookups of git refs
+
+    GitRefLookup objects delegate to the misc_cache for locking. GitRefLookup objects may
+    be attached to a GitVersion to allow for comparisons between git refs and versions as
+    represented by tags in the git repository.
+    """
+
+    def __init__(self, pkg_name):
+        self.pkg_name = pkg_name
+
+        self.data: Dict[str, Tuple[Optional[str], int]] = {}
+
+        self._pkg = None
+        self._fetcher = None
+        self._cache_key = None
+        self._cache_path = None
+
+    # The following properties are used as part of a lazy reference scheme
+    # to avoid querying the package repository until it is necessary (and
+    # in particular to wait until after the configuration has been
+    # assembled)
+    @property
+    def cache_key(self):
+        if not self._cache_key:
+            key_base = "git_metadata"
+            if not self.repository_uri.startswith("/"):
+                key_base += "/"
+            self._cache_key = key_base + self.repository_uri
+
+            # Cache data in misc_cache
+            # If this is the first lazy access, initialize the cache as well
+            spack.caches.misc_cache.init_entry(self.cache_key)
+        return self._cache_key
+
+    @property
+    def cache_path(self):
+        if not self._cache_path:
+            self._cache_path = spack.caches.misc_cache.cache_path(self.cache_key)
+        return self._cache_path
+
+    @property
+    def pkg(self):
+        if not self._pkg:
+            try:
+                pkg = spack.repo.path.get_pkg_class(self.pkg_name)
+                pkg.git
+            except (spack.repo.RepoError, AttributeError) as e:
+                raise VersionLookupError(f"Couldn't get the git repo for {self.pkg_name}") from e
+            self._pkg = pkg
+        return self._pkg
+
+    @property
+    def fetcher(self):
+        if not self._fetcher:
+            # We require the full git repository history
+            fetcher = spack.fetch_strategy.GitFetchStrategy(git=self.pkg.git)
+            fetcher.get_full_repo = True
+            self._fetcher = fetcher
+        return self._fetcher
+
+    @property
+    def repository_uri(self):
+        """Identifier for git repos used within the repo and metadata caches."""
+        try:
+            components = [
+                str(c).lstrip("/") for c in spack.util.url.parse_git_url(self.pkg.git) if c
+            ]
+            return os.path.join(*components)
+        except ValueError:
+            # If it's not a git url, it's a local path
+            return os.path.abspath(self.pkg.git)
+
+    def save(self):
+        """Save the data to file"""
+        with spack.caches.misc_cache.write_transaction(self.cache_key) as (old, new):
+            sjson.dump(self.data, new)
+
+    def load_data(self):
+        """Load data if the path already exists."""
+        if os.path.isfile(self.cache_path):
+            with spack.caches.misc_cache.read_transaction(self.cache_key) as cache_file:
+                self.data = sjson.load(cache_file)
+
+    def get(self, ref) -> Tuple[Optional[str], int]:
+        if not self.data:
+            self.load_data()
+
+        if ref not in self.data:
+            self.data[ref] = self.lookup_ref(ref)
+            self.save()
+
+        return self.data[ref]
+
+    def lookup_ref(self, ref) -> Tuple[Optional[str], int]:
+        """Lookup the previous version and distance for a given commit.
+
+        We use git to compare the known versions from package to the git tags,
+        as well as any git tags that are SEMVER versions, and find the latest
+        known version prior to the commit, as well as the distance from that version
+        to the commit in the git repo. Those values are used to compare Version objects.
+        """
+        dest = os.path.join(spack.paths.user_repos_cache_path, self.repository_uri)
+        if dest.endswith(".git"):
+            dest = dest[:-4]
+
+        # prepare a cache for the repository
+        dest_parent = os.path.dirname(dest)
+        if not os.path.exists(dest_parent):
+            mkdirp(dest_parent)
+
+        # Only clone if we don't have it!
+        if not os.path.exists(dest):
+            self.fetcher.clone(dest, bare=True)
+
+        # Lookup commit info
+        with working_dir(dest):
+            # TODO: we need to update the local tags if they changed on the
+            # remote instance, simply adding '-f' may not be sufficient
+            # (if commits are deleted on the remote, this command alone
+            # won't properly update the local rev-list)
+            self.fetcher.git("fetch", "--tags", output=os.devnull, error=os.devnull)
+
+            # Ensure ref is a commit object known to git
+            # Note the brackets are literals, the ref replaces the format string
+            try:
+                self.fetcher.git(
+                    "cat-file", "-e", "%s^{commit}" % ref, output=os.devnull, error=os.devnull
+                )
+            except spack.util.executable.ProcessError:
+                raise VersionLookupError("%s is not a valid git ref for %s" % (ref, self.pkg_name))
+
+            # List tags (refs) by date, so last reference of a tag is newest
+            tag_info = self.fetcher.git(
+                "for-each-ref",
+                "--sort=creatordate",
+                "--format",
+                "%(objectname) %(refname)",
+                "refs/tags",
+                output=str,
+            ).split("\n")
+
+            # Lookup of commits to spack versions
+            commit_to_version = {}
+
+            for entry in tag_info:
+                if not entry:
+                    continue
+                tag_commit, tag = entry.split()
+                tag = tag.replace("refs/tags/", "", 1)
+
+                # For each tag, try to match to a version
+                for v in [v.string for v in self.pkg.versions]:
+                    if v == tag or "v" + v == tag:
+                        commit_to_version[tag_commit] = v
+                        break
+                else:
+                    # try to parse tag to copare versions spack does not know
+                    match = SEMVER_REGEX.match(tag)
+                    if match:
+                        semver = match.groupdict()["semver"]
+                        commit_to_version[tag_commit] = semver
+
+            ancestor_commits = []
+            for tag_commit in commit_to_version:
+                self.fetcher.git("merge-base", "--is-ancestor", tag_commit, ref, ignore_errors=[1])
+                if self.fetcher.git.returncode == 0:
+                    distance = self.fetcher.git(
+                        "rev-list", "%s..%s" % (tag_commit, ref), "--count", output=str, error=str
+                    ).strip()
+                    ancestor_commits.append((tag_commit, int(distance)))
+
+            if ancestor_commits:
+                # Get nearest ancestor that is a known version
+                prev_version_commit, distance = min(ancestor_commits, key=lambda x: x[1])
+                prev_version = commit_to_version[prev_version_commit]
+            else:
+                # Get list of all commits, this is in reverse order
+                # We use this to get the first commit below
+                ref_info = self.fetcher.git("log", "--all", "--pretty=format:%H", output=str)
+                commits = [c for c in ref_info.split("\n") if c]
+
+                # No previous version and distance from first commit
+                prev_version = None
+                distance = int(
+                    self.fetcher.git(
+                        "rev-list", "%s..%s" % (commits[-1], ref), "--count", output=str, error=str
+                    ).strip()
+                )
+
+        return prev_version, distance
diff --git a/lib/spack/spack/version/lookup.py b/lib/spack/spack/version/lookup.py
new file mode 100644
index 0000000000..e33b5c2176
--- /dev/null
+++ b/lib/spack/spack/version/lookup.py
@@ -0,0 +1,17 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from typing import Optional, Tuple
+
+
+class AbstractRefLookup:
+    def get(self, ref) -> Tuple[Optional[str], int]:
+        """Get the version string and distance for a given git ref.
+
+        Args:
+            ref (str): git ref to lookup
+
+        Returns: optional version string and distance"""
+        return None, 0
diff --git a/lib/spack/spack/version.py b/lib/spack/spack/version/version_types.py
index 4be1afd90c..223cad40d6 100644
--- a/lib/spack/spack/version.py
+++ b/lib/spack/spack/version/version_types.py
@@ -3,54 +3,28 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
-"""
-This module implements Version and version-ish objects.  These are:
-
-StandardVersion: A single version of a package.
-ClosedOpenRange: A range of versions of a package.
-VersionList: A ordered list of Version and VersionRange elements.
-
-The set of Version and ClosedOpenRange is totally ordered wiht <
-defined as Version(x) < VersionRange(Version(y), Version(x))
-if Version(x) <= Version(y).
-"""
 import numbers
-import os
 import re
 from bisect import bisect_left
-from typing import Dict, List, Optional, Tuple, Union
-
-from llnl.util.filesystem import mkdirp, working_dir
+from typing import List, Optional, Tuple, Union
 
-import spack.caches
-import spack.error
-import spack.paths
-import spack.util.executable
-import spack.util.spack_json as sjson
-import spack.util.url
 from spack.util.spack_yaml import syaml_dict
 
+from .common import (
+    COMMIT_VERSION,
+    VersionLookupError,
+    infinity_versions,
+    is_git_version,
+    iv_min_len,
+)
+from .lookup import AbstractRefLookup
+
 # Valid version characters
 VALID_VERSION = re.compile(r"^[A-Za-z0-9_.-][=A-Za-z0-9_.-]*$")
 
-# regex for a commit version
-COMMIT_VERSION = re.compile(r"^[a-f0-9]{40}$")
-
 # regex for version segments
 SEGMENT_REGEX = re.compile(r"(?:(?P<num>[0-9]+)|(?P<str>[a-zA-Z]+))(?P<sep>[_.-]*)")
 
-# regular expression for semantic versioning
-SEMVER_REGEX = re.compile(
-    ".+(?P<semver>([0-9]+)[.]([0-9]+)[.]([0-9]+)"
-    "(?:-([0-9A-Za-z-]+(?:[.][0-9A-Za-z-]+)*))?"
-    "(?:[+][0-9A-Za-z-]+)?)"
-)
-
-# Infinity-like versions. The order in the list implies the comparison rules
-infinity_versions = ["stable", "trunk", "head", "master", "main", "develop"]
-
-iv_min_len = min(len(s) for s in infinity_versions)
-
 
 class VersionStrComponent:
     __slots__ = ["data"]
@@ -407,7 +381,7 @@ class GitVersion(ConcreteVersion):
 
     def __init__(self, string: str):
         # An object that can lookup git refs to compare them to versions
-        self._ref_lookup: Optional[CommitLookup] = None
+        self._ref_lookup: Optional[AbstractRefLookup] = None
 
         # This is the effective version.
         self._ref_version: Optional[StandardVersion]
@@ -440,8 +414,7 @@ class GitVersion(ConcreteVersion):
 
         if self.ref_lookup is None:
             raise VersionLookupError(
-                f"git ref '{self.ref}' cannot be looked up: "
-                "call attach_git_lookup_from_package first"
+                f"git ref '{self.ref}' cannot be looked up: " "call attach_lookup first"
             )
 
         version_string, distance = self.ref_lookup.get(self.ref)
@@ -573,7 +546,7 @@ class GitVersion(ConcreteVersion):
             self._ref_lookup.get(self.ref)
             return self._ref_lookup
 
-    def attach_git_lookup_from_package(self, pkg_name):
+    def attach_lookup(self, lookup: AbstractRefLookup):
         """
         Use the git fetcher to look up a version for a commit.
 
@@ -585,7 +558,7 @@ class GitVersion(ConcreteVersion):
         alongside the GitFetcher because eventually the git repos cache will
         be one and the same with the source cache.
         """
-        self._ref_lookup = self._ref_lookup or CommitLookup(pkg_name)
+        self._ref_lookup = lookup
 
     def __iter__(self):
         return self.ref_version.__iter__()
@@ -758,7 +731,7 @@ class VersionList:
         if vlist is not None:
             if isinstance(vlist, str):
                 vlist = from_string(vlist)
-                if type(vlist) == VersionList:
+                if isinstance(vlist, VersionList):
                     self.versions = vlist.versions
                 else:
                     self.versions = [vlist]
@@ -792,7 +765,7 @@ class VersionList:
 
             self.versions.insert(i, item)
 
-        elif type(item) == VersionList:
+        elif isinstance(item, VersionList):
             for v in item:
                 self.add(v)
 
@@ -1073,15 +1046,6 @@ def prev_version(v: StandardVersion) -> StandardVersion:
     return StandardVersion("".join(string_components), v.version[:-1] + (prev,), v.separators)
 
 
-def is_git_version(string: str) -> bool:
-    return (
-        string.startswith("git.")
-        or len(string) == 40
-        and bool(COMMIT_VERSION.match(string))
-        or "=" in string[1:]
-    )
-
-
 def Version(string: Union[str, int]) -> Union[GitVersion, StandardVersion]:
     if not isinstance(string, (str, int)):
         raise ValueError(f"Cannot construct a version from {type(string)}")
@@ -1140,216 +1104,3 @@ def ver(obj) -> Union[VersionList, ClosedOpenRange, StandardVersion, GitVersion]
         return obj
     else:
         raise TypeError("ver() can't convert %s to version!" % type(obj))
-
-
-#: This version contains all possible versions.
-any_version: VersionList = VersionList([":"])
-
-
-class VersionError(spack.error.SpackError):
-    """This is raised when something is wrong with a version."""
-
-
-class VersionChecksumError(VersionError):
-    """Raised for version checksum errors."""
-
-
-class VersionLookupError(VersionError):
-    """Raised for errors looking up git commits as versions."""
-
-
-class CommitLookup:
-    """An object for cached lookups of git commits
-
-    CommitLookup objects delegate to the misc_cache for locking. CommitLookup objects may
-    be attached to a GitVersion to allow for comparisons between git refs and versions as
-    represented by tags in the git repository.
-    """
-
-    def __init__(self, pkg_name):
-        self.pkg_name = pkg_name
-
-        self.data: Dict[str, Tuple[Optional[str], int]] = {}
-
-        self._pkg = None
-        self._fetcher = None
-        self._cache_key = None
-        self._cache_path = None
-
-    # The following properties are used as part of a lazy reference scheme
-    # to avoid querying the package repository until it is necessary (and
-    # in particular to wait until after the configuration has been
-    # assembled)
-    @property
-    def cache_key(self):
-        if not self._cache_key:
-            key_base = "git_metadata"
-            if not self.repository_uri.startswith("/"):
-                key_base += "/"
-            self._cache_key = key_base + self.repository_uri
-
-            # Cache data in misc_cache
-            # If this is the first lazy access, initialize the cache as well
-            spack.caches.misc_cache.init_entry(self.cache_key)
-        return self._cache_key
-
-    @property
-    def cache_path(self):
-        if not self._cache_path:
-            self._cache_path = spack.caches.misc_cache.cache_path(self.cache_key)
-        return self._cache_path
-
-    @property
-    def pkg(self):
-        if not self._pkg:
-            import spack.repo  # break cycle
-
-            try:
-                pkg = spack.repo.path.get_pkg_class(self.pkg_name)
-                pkg.git
-            except (spack.repo.RepoError, AttributeError) as e:
-                raise VersionLookupError(f"Couldn't get the git repo for {self.pkg_name}") from e
-            self._pkg = pkg
-        return self._pkg
-
-    @property
-    def fetcher(self):
-        if not self._fetcher:
-            # We require the full git repository history
-            import spack.fetch_strategy  # break cycle
-
-            fetcher = spack.fetch_strategy.GitFetchStrategy(git=self.pkg.git)
-            fetcher.get_full_repo = True
-            self._fetcher = fetcher
-        return self._fetcher
-
-    @property
-    def repository_uri(self):
-        """Identifier for git repos used within the repo and metadata caches."""
-        try:
-            components = [
-                str(c).lstrip("/") for c in spack.util.url.parse_git_url(self.pkg.git) if c
-            ]
-            return os.path.join(*components)
-        except ValueError:
-            # If it's not a git url, it's a local path
-            return os.path.abspath(self.pkg.git)
-
-    def save(self):
-        """Save the data to file"""
-        with spack.caches.misc_cache.write_transaction(self.cache_key) as (old, new):
-            sjson.dump(self.data, new)
-
-    def load_data(self):
-        """Load data if the path already exists."""
-        if os.path.isfile(self.cache_path):
-            with spack.caches.misc_cache.read_transaction(self.cache_key) as cache_file:
-                self.data = sjson.load(cache_file)
-
-    def get(self, ref) -> Tuple[Optional[str], int]:
-        if not self.data:
-            self.load_data()
-
-        if ref not in self.data:
-            self.data[ref] = self.lookup_ref(ref)
-            self.save()
-
-        return self.data[ref]
-
-    def lookup_ref(self, ref) -> Tuple[Optional[str], int]:
-        """Lookup the previous version and distance for a given commit.
-
-        We use git to compare the known versions from package to the git tags,
-        as well as any git tags that are SEMVER versions, and find the latest
-        known version prior to the commit, as well as the distance from that version
-        to the commit in the git repo. Those values are used to compare Version objects.
-        """
-        dest = os.path.join(spack.paths.user_repos_cache_path, self.repository_uri)
-        if dest.endswith(".git"):
-            dest = dest[:-4]
-
-        # prepare a cache for the repository
-        dest_parent = os.path.dirname(dest)
-        if not os.path.exists(dest_parent):
-            mkdirp(dest_parent)
-
-        # Only clone if we don't have it!
-        if not os.path.exists(dest):
-            self.fetcher.clone(dest, bare=True)
-
-        # Lookup commit info
-        with working_dir(dest):
-            # TODO: we need to update the local tags if they changed on the
-            # remote instance, simply adding '-f' may not be sufficient
-            # (if commits are deleted on the remote, this command alone
-            # won't properly update the local rev-list)
-            self.fetcher.git("fetch", "--tags", output=os.devnull, error=os.devnull)
-
-            # Ensure ref is a commit object known to git
-            # Note the brackets are literals, the ref replaces the format string
-            try:
-                self.fetcher.git(
-                    "cat-file", "-e", "%s^{commit}" % ref, output=os.devnull, error=os.devnull
-                )
-            except spack.util.executable.ProcessError:
-                raise VersionLookupError("%s is not a valid git ref for %s" % (ref, self.pkg_name))
-
-            # List tags (refs) by date, so last reference of a tag is newest
-            tag_info = self.fetcher.git(
-                "for-each-ref",
-                "--sort=creatordate",
-                "--format",
-                "%(objectname) %(refname)",
-                "refs/tags",
-                output=str,
-            ).split("\n")
-
-            # Lookup of commits to spack versions
-            commit_to_version = {}
-
-            for entry in tag_info:
-                if not entry:
-                    continue
-                tag_commit, tag = entry.split()
-                tag = tag.replace("refs/tags/", "", 1)
-
-                # For each tag, try to match to a version
-                for v in [v.string for v in self.pkg.versions]:
-                    if v == tag or "v" + v == tag:
-                        commit_to_version[tag_commit] = v
-                        break
-                else:
-                    # try to parse tag to copare versions spack does not know
-                    match = SEMVER_REGEX.match(tag)
-                    if match:
-                        semver = match.groupdict()["semver"]
-                        commit_to_version[tag_commit] = semver
-
-            ancestor_commits = []
-            for tag_commit in commit_to_version:
-                self.fetcher.git("merge-base", "--is-ancestor", tag_commit, ref, ignore_errors=[1])
-                if self.fetcher.git.returncode == 0:
-                    distance = self.fetcher.git(
-                        "rev-list", "%s..%s" % (tag_commit, ref), "--count", output=str, error=str
-                    ).strip()
-                    ancestor_commits.append((tag_commit, int(distance)))
-
-            if ancestor_commits:
-                # Get nearest ancestor that is a known version
-                prev_version_commit, distance = min(ancestor_commits, key=lambda x: x[1])
-                prev_version = commit_to_version[prev_version_commit]
-            else:
-                # Get list of all commits, this is in reverse order
-                # We use this to get the first commit below
-                ref_info = self.fetcher.git("log", "--all", "--pretty=format:%H", output=str)
-                commits = [c for c in ref_info.split("\n") if c]
-
-                # No previous version and distance from first commit
-                prev_version = None
-                distance = int(
-                    self.fetcher.git(
-                        "rev-list", "%s..%s" % (commits[-1], ref), "--count", output=str, error=str
-                    ).strip()
-                )
-
-        return prev_version, distance