bazel: generate license list for documentation.

Example:

    $ bazel build //Documentation:pgm-licenses.txt
    ..
    $ cat bazel-genfiles/Documentation/pgm-licenses.txt
    //lib:jsch //lib:LICENSE-jsch
    //lib:servlet-api-3_1 //lib:LICENSE-Apache2.0

Still missing:

* check that there are dependencies on forbidden licenses

* check that there are no external dependencies except through the
  //lib directory.

Change-Id: I8f0ed94de20f68e0dbc1fe87dfd56ce11e02fab7

tools/bzl/license-map.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python
+
+# reads a bazel query XML file, to join target names with their licenses.
+
+import sys
+import xml.etree.ElementTree as ET
+
+tree = ET.parse(sys.argv[1])
+root = tree.getroot()
+
+entries = {}
+
+for child in root:
+  rule_name = child.attrib["name"]
+  for c in child.getchildren():
+    if c.tag != "rule-input":
+      continue
+
+    license_name = c.attrib["name"]
+    if "//lib:LICENSE" in license_name:
+      assert rule_name not in entries, (license_name, entries[rule_name])
+      entries[rule_name] = license_name
+
+for k, v in sorted(entries.items()):
+  print k, v