fix: parsing of Git version

Author: abrown

version

@@ -33,20 +33,50 @@ def main(action, llvm_dir):
 def git_version():
     version = exec(['git', 'describe', '--long', '--candidates=999',
                     '--match=wasi-sdk-*', '--dirty=+m', f'--abbrev={GIT_REF_LEN}'])
-    # Parse, e.g.: wasi-sdk-21-0-g317548590b40+m
-    parts = version.replace('+', '-').split('-')
-    assert (parts[0:2] == ['wasi', 'sdk'])
-    major, minor, git, dirty = parts[2:]
+    major, minor, git, dirty = parse_git_version(version)
     version = f'{major}.{minor}'
     if git:
-        assert (git.startswith('g'))
-        version += git
+        version += f'g{git}'
     if dirty:
-        assert (dirty == 'm')
         version += '+m'
     return version
 
 
+def parse_git_version(version):
+    # Parse, e.g.: wasi-sdk-21-0-g317548590b40+m
+    parts = version.replace('+', '-').split('-')
+    assert parts.pop(0) == 'wasi'
+    assert parts.pop(0) == 'sdk'
+
+    major, minor = parts.pop(0), parts.pop(0)
+    git = None
+    dirty = False
+
+    if parts:
+        # Check: git|dirty.
+        next = parts.pop(0)
+        if next == 'm':
+            dirty = True
+        else:
+            git = next[1:]
+
+        # Check: dirty.
+        if parts:
+            assert parts.pop(0) == 'm', f'expected dirty flag: +m'
+            dirty = True
+
+    assert not parts, f'unexpected suffixes: {parts}'
+    return major, minor, git, dirty
+
+
+# Some inline tests to check Git version parsing:
+assert parse_git_version(
+    'wasi-sdk-21-0-g317548590b40+m') == ('21', '0', '317548590b40', True)
+assert parse_git_version('wasi-sdk-21-2+m') == ('21', '2', None, True)
+assert parse_git_version(
+    'wasi-sdk-23-0-g317548590b40') == ('23', '0', '317548590b40', False)
+
+
 def git_commit(dir='.'):
     return exec(['git', 'rev-parse', f'--short={GIT_REF_LEN}', 'HEAD'], dir)