update script to update exsting checkout

Makefile

@@ -50,23 +50,21 @@ flake8:
 	@echo 'tox -e flake8' is preferred to 'make flake8'
 	$(PYTHON) -m flake8 $(CHECK_DIRS) --exclude gettext38.py,contextlib38.py
 
-unit:
+unit: gitdeps
 	python3 -m unittest discover
 
-integration:
+integration: gitdeps
 	echo "Running integration tests..."
 	./scripts/runtests.sh
 
 check: unit integration
 
-curtin:
-	./scripts/checkout-part.py curtin
+curtin: snapcraft.yaml
+	./scripts/update-part.py curtin
 
-probert:
-	@if [ ! -d "$(PROBERTDIR)" ]; then \
-		./scripts/checkout-part.py probert && \
-		(cd probert && $(PYTHON) setup.py build_ext -i); \
-	fi
+probert: snapcraft.yaml
+	./scripts/update-part.py probert
+	(cd probert && $(PYTHON) setup.py build_ext -i);
 
 gitdeps: curtin probert
 

scripts/checkout-part.py

@@ -1,27 +0,0 @@
-#!/usr/bin/python3
-import subprocess
-import sys
-import yaml
-
-part = sys.argv[1]
-
-
-def r(*args):
-    print('running', args)
-    subprocess.run(args, check=True)
-
-
-with open("snapcraft.yaml") as f:
-    config = yaml.safe_load(f)["parts"][part]
-
-r('git', 'clone', config['source'], part)
-
-
-c = None
-for k in "source-commit", "source-tag", "source-branch":
-    if k in config:
-        c = config[k]
-        break
-
-if c is not None:
-    r('git', '-c', 'advice.detachedHead=false', '-C', part, 'checkout', c)

scripts/update-part.py

@@ -0,0 +1,40 @@
+#!/usr/bin/python3
+import os
+import subprocess
+import sys
+import yaml
+
+part = sys.argv[1]
+
+
+def r(*args, **kw):
+    print('running', args)
+    subprocess.run(args, check=True, **kw)
+
+
+def o(*args, **kw):
+    return subprocess.run(args, check=True, stdout=subprocess.PIPE).stdout
+
+
+with open("snapcraft.yaml") as f:
+    config = yaml.safe_load(f)["parts"][part]
+
+
+c = "master"
+for k in "source-commit", "source-tag", "source-branch":
+    if k in config:
+        c = config[k]
+        break
+
+if not os.path.isdir(part):
+    r('git', 'clone', config['source'], part)
+
+expected = o('git', '-C', part, 'rev-parse', c)
+actual = o('git', '-C', part, 'rev-parse', 'HEAD')
+
+if expected != actual:
+    try:
+        r('git', '-c', 'advice.detachedHead=false', '-C', part, 'checkout', c)
+    except subprocess.CalledProcessError:
+        r('git', '-C', part, 'fetch', config['source'])
+        r('git', '-c', 'advice.detachedHead=false', '-C', part, 'checkout', c)