Some more work on the new dependency resolution system.

recipes/libpng/recipe.py

@@ -1,6 +1,28 @@
 
+import re
 from SCons.Script import *
 
+_REPO_NAME = 'libpng'
+_REPO_URL = 'https://git.code.sf.net/p/libpng/code.git'
+_TAG_PATTERN = re.compile(r'^v([0-9])+\.([0-9])+\.([0-9])$')
+
+def available(env: Environment) -> bool:
+    return hasattr(env, 'GitBranch') and hasattr(env, 'GitTags')
+
+def versions(env: Environment, update: bool = False) -> 'list[str]':
+    tags = env.GitTags(repo_name = _REPO_NAME, remote_url = _REPO_URL, force_fetch=update)
+    result = []
+    for tag in tags:
+        match = _TAG_PATTERN.match(tag)
+        if match:
+            result.append((int(match.groups()[0]), int(match.groups()[1]), int(match.groups()[2])))
+    return result
+
+def dependencies(env: Environment, version) -> 'list[dict]':
+    return {
+        'zlib': {}
+    }
+
 def cook(env: Environment, git_ref = 'master') -> dict:
     lib_z = env.Cook('zlib')
     repo = env.GitBranch(repo_name = 'libpng', remote_url = 'https://git.code.sf.net/p/libpng/code.git', git_ref = git_ref)