1 files changed, 86 insertions, 0 deletions
diff --git a/documentation/sphinx/yocto-vars.py b/documentation/sphinx/yocto-vars.py
new file mode 100644
index 0000000000..643c0df904
--- /dev/null
+++ b/documentation/sphinx/yocto-vars.py
@@ -0,0 +1,86 @@
+#!/usr/bin/env python
+from hashlib import md5
+from pathlib import Path
+import re
+import sys
+
+import sphinx
+from sphinx.application import Sphinx
+
+# This extension uses pyyaml, report an explicit
+# error message if it's not installed
+try:
+    import yaml
+except ImportError:
+    sys.stderr.write("The Yocto Project Sphinx documentation requires PyYAML.\
+    \nPlease make sure to install pyyaml Python package.\n")
+    sys.exit(1)
+
+__version__  = '1.0'
+
+# Variables substitutions. Uses {VAR} subst using variables defined in poky.yaml
+# Each .rst file is processed after source-read event (subst_vars_replace runs once per file)
+subst_vars = {}
+
+poky_hash = ""
+
+def subst_vars_replace(app: Sphinx, docname, source):
+    result = source[0]
+    for k in subst_vars:
+        result = result.replace("&"+k+";", subst_vars[k])
+    source[0] = result
+
+def yocto_vars_env_get_outdated(app: Sphinx, env, added, changed, removed):
+    '''
+    If poky.yaml changed (BUILDDIR/.poky.yaml.cache does not exist or contains
+    an md5sum different from poky.yaml's current md5sum), force rebuild of all
+    *.rst files in SOURCEDIR whose content has at least one occurence of `&.*;`
+    (see PATTERN global variable).
+    '''
+    try:
+        poky_cache = Path(app.outdir) / ".poky.yaml.cache"
+        cache_hash = poky_cache.read_text()
+    except FileNotFoundError:
+        cache_hash = None
+
+    if poky_hash == cache_hash:
+        return []
+
+    docs = []
+    for p in Path(app.srcdir).rglob("*.rst"):
+        if PATTERN.search(p.read_text()):
+            p_rel_no_ext = p.relative_to(app.srcdir).parent / p.stem
+            docs.append(str(p_rel_no_ext))
+    return docs
+
+def yocto_vars_build_finished(app: Sphinx, exception):
+    poky_cache = Path(app.outdir) / ".poky.yaml.cache"
+    poky_cache.write_text(poky_hash)
+    return []
+
+PATTERN = re.compile(r'&(.*?);')
+def expand(val, src):
+    return PATTERN.sub(lambda m: expand(src.get(m.group(1), ''), src), val)
+
+def setup(app: Sphinx):
+    global poky_hash
+
+    with open("poky.yaml") as file:
+        hasher = md5()
+        buff = file.read()
+        hasher.update(buff.encode('utf-8'))
+        poky_hash = hasher.hexdigest()
+        subst_vars.update(yaml.safe_load(buff))
+
+    for k in subst_vars:
+        subst_vars[k] = expand(subst_vars[k], subst_vars)
+
+    app.connect('source-read', subst_vars_replace)
+    app.connect('env-get-outdated', yocto_vars_env_get_outdated)
+    app.connect('build-finished', yocto_vars_build_finished)
+
+    return dict(
+        version = __version__,
+        parallel_read_safe = True,
+        parallel_write_safe = True
+    )