Start

diff --git a/nix_pin_deps.py b/nix_pin_deps.py
new file mode 100644 (file)
index 0000000..20988f5
--- /dev/null
+++ b/nix_pin_deps.py
@@ -0,0 +1,100 @@
+from contextlib import contextmanager
+import json
+import os
+import subprocess
+import sys
+import xml.sax
+import xml.sax.handler
+
+
+@contextmanager
+def log(msg):
+    print(msg, file=sys.stderr, end='', flush=True)
+    try:
+        yield
+    finally:
+        print('\r', file=sys.stderr, end='', flush=True)
+
+
+class ParseNixStoreQueryGraphML(xml.sax.handler.ContentHandler):
+    def __init__(self):
+        self.roots = set()
+        self.non_roots = set()
+        self.deps = {}
+
+    def startElement(self, name, attrs):
+        if name == "edge":
+            source = attrs.getValue("source")
+            target = attrs.getValue("target")
+            self.non_roots.add(target)
+            self.deps.setdefault(source, []).append(target)
+            if target in self.roots:
+                self.roots.remove(target)
+            if source not in self.non_roots:
+                self.roots.add(source)
+
+
+def getDeps(drv):
+    with log("Loading dependency tree..."):
+        process = subprocess.Popen(
+            ["nix-store", "--query", "--graphml", drv], stdout=subprocess.PIPE)
+        parser = ParseNixStoreQueryGraphML()
+        xml.sax.parse(process.stdout, parser)
+        assert process.wait() == 0
+        return parser
+
+
+def getDrvInfo(drv):
+    with log("Loading %s..." % drv):
+        process = subprocess.Popen(["nix",
+                                    "--experimental-features",
+                                    "nix-command",
+                                    "show-derivation",
+                                    "/nix/store/" + drv],
+                                   stdout=subprocess.PIPE)
+        info = json.load(process.stdout)
+        assert process.wait() == 0
+        return info
+
+
+def allBuilt(drv):
+    # TODO: How to pin outputs one at a time?
+    # Currently, we only pin when all outputs are available.
+    # It would be better to pin the outputs we've got.
+    return all(os.path.exists(o['path']) for d in getDrvInfo(
+        drv).values() for o in d['outputs'].values())
+
+
+def isDrv(thing):
+    return thing.endswith(".drv")
+
+
+def removesuffix(s, suf):
+    return s[:-len(suf)] if s.endswith(suf) else s
+
+
+def pin(drv):
+    outPath = os.path.join(sys.argv[2], removesuffix(drv, ".drv"))
+    if not os.path.exists(outPath):
+        process = subprocess.run(["nix-store",
+                                  "--realise",
+                                  "--add-root",
+                                  outPath,
+                                  "/nix/store/" + drv],
+                                 check=True)
+
+
+def pinBuiltThings(thing, done, deps):
+    if thing in done:
+        return
+    done.add(thing)
+    if not isDrv(thing) or allBuilt(thing):
+        pin(thing)
+        return
+    for dep in deps.get(thing, []):
+        pinBuiltThings(dep, done, deps)
+
+
+dep_graph = getDeps(sys.argv[1])
+for root in dep_graph.roots:
+    pinBuiltThings(root, set(), dep_graph.deps)