[gnome-continuous-yocto/gnomeostree-3.28-rocko: 5463/8267] bitbake: codeparser: add some comments

[Emmanuele Bassi <ebassi src gnome org>]

commit 2d704e445c220be1793570bfeaa95619676f1f19
Author: Paul Eggleton <paul eggleton linux intel com>
Date:   Mon Apr 3 11:19:06 2017 +1200

    bitbake: codeparser: add some comments
    
    Add a few comments at the top of the file explaining what it's for, and
    a comment pointing out that you need to increment the cache version when
    changing any code that changes the output.
    
    (Bitbake rev: c1780bc1872bb35bc28c76eff9110717f02d9db2)
    
    Signed-off-by: Paul Eggleton <paul eggleton linux intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 bitbake/lib/bb/codeparser.py |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)
---
diff --git a/bitbake/lib/bb/codeparser.py b/bitbake/lib/bb/codeparser.py
index f76b478..530f44e 100644
--- a/bitbake/lib/bb/codeparser.py
+++ b/bitbake/lib/bb/codeparser.py
@@ -1,3 +1,22 @@
+"""
+BitBake code parser
+
+Parses actual code (i.e. python and shell) for functions and in-line
+expressions. Used mainly to determine dependencies on other functions
+and variables within the BitBake metadata. Also provides a cache for
+this information in order to speed up processing.
+
+(Not to be confused with the code that parses the metadata itself,
+see lib/bb/parse/ for that).
+
+NOTE: if you change how the parsers gather information you will almost
+certainly need to increment CodeParserCache.CACHE_VERSION below so that
+any existing codeparser cache gets invalidated. Additionally you'll need
+to increment __cache_version__ in cache.py in order to ensure that old
+recipe caches don't trigger "Taskhash mismatch" errors.
+
+"""
+
 import ast
 import sys
 import codegen
@@ -117,6 +136,10 @@ class shellCacheLine(object):
 
 class CodeParserCache(MultiProcessCache):
     cache_file_name = "bb_codeparser.dat"
+    # NOTE: you must increment this if you change how the parsers gather information,
+    # so that an existing cache gets invalidated. Additionally you'll need
+    # to increment __cache_version__ in cache.py in order to ensure that old
+    # recipe caches don't trigger "Taskhash mismatch" errors.
     CACHE_VERSION = 9
 
     def __init__(self):