Add comments.

src/etc/errorck.py

@@ -23,6 +23,15 @@
 errcode_map = {}
 error_re = re.compile("(E\d\d\d\d)")
 
+# In the register_long_diagnostics! macro, entries look like this:
+#
+# EXXXX: r##"
+# <Long diagnostic message>
+# "##,
+#
+# These two variables are for detecting the beginning and end of diagnostic
+# messages so that duplicate error codes are not reported when a code occurs
+# inside a diagnostic message
 long_diag_begin = "r##\""
 long_diag_end = "\"##"
 
@@ -41,6 +50,7 @@
             inside_long_diag = False
             for line_num, line in enumerate(f, start=1):
                 if inside_long_diag:
+                    # Skip duplicate error code checking for this line
                     if long_diag_end in line:
                         inside_long_diag = False
                     continue