--- /dev/null
+Configure Internals
+===================
+
+[ note: this file uses markdown for formatting ]
+
+Intro
+-----
+
+This is a collection of notes that are hopefully of interest to those
+who decide to dive into Configure and what it does. This is a living
+document and anyone is encouraged to add to it and submit changes.
+There's no claim for this document to be complete at any time, but it
+will hopefully reach such a point in time.
+
+
+----------------------------------------------------------------------
+
+Parsing build.info files, processing conditions
+-----------------------------------------------
+
+Processing conditions in build.info files is done with the help of a
+condition stack that tell if a build.info should be processed or if it
+should just be skipped over. The possible states of the stack top are
+expressed in the following comment from Configure:
+
+ # The top item of this stack has the following values
+ # -2 positive already run and we found ELSE (following ELSIF should fail)
+ # -1 positive already run (skip until ENDIF)
+ # 0 negatives so far (if we're at a condition, check it)
+ # 1 last was positive (don't skip lines until next ELSE, ELSIF or ENDIF)
+ # 2 positive ELSE (following ELSIF should fail)
+
+Ground rule is that non-condition lines are skipped over if the
+stack top is > 0. Condition lines (IF, ELSIF, ELSE and ENDIF
+statements) need to be processed either way to keep track of the skip
+stack states, so they are a little more intricate.
+
+Instead of trying to describe in words, here are some example of what
+the skip stack should look like after each line is processed:
+
+Example 1:
+
+| IF[1] | 1 | |
+| ... whatever ... | | this line is processed |
+| IF[1] | 1 1 | |
+| ... whatever ... | | this line is processed |
+| ELSIF[1] | 1 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 1 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 1 | |
+| ... whatever ... | | this line is processed |
+| ELSIF[1] | -1 | |
+| ... whatever ... | | this line is skipped over |
+| IF[1] | -1 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | -1 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | -1 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | -1 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | | |
+
+Example 2:
+
+| IF[0] | 0 | |
+| ... whatever ... | | this line is skipped over |
+| IF[1] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 0 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 1 | |
+| ... whatever ... | | this line is processed |
+| IF[1] | 1 1 | |
+| ... whatever ... | | this line is processed |
+| ELSIF[1] | 1 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 1 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 1 | |
+| ... whatever ... | | this line is processed |
+| ENDIF | | |
+
+Example 3:
+
+| IF[0] | 0 | |
+| ... whatever ... | | this line is skipped over |
+| IF[0] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 0 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 1 | |
+| ... whatever ... | | this line is processed |
+| IF[0] | 1 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 1 1 | |
+| ... whatever ... | | this line is processed |
+| ELSE | 1 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 1 | |
+| ... whatever ... | | this line is processed |
+| ENDIF | | |
+
+Example 4:
+
+| IF[0] | 0 | |
+| ... whatever ... | | this line is skipped over |
+| IF[0] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[0] | 0 -1 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 0 -2 | |
+| ... whatever ... | | this line is skipped over |
+| ENDIF | 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[1] | 1 | |
+| ... whatever ... | | this line is processed |
+| IF[0] | 1 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSIF[0] | 1 0 | |
+| ... whatever ... | | this line is skipped over |
+| ELSE | 1 2 | |
+| ... whatever ... | | this line is processed |
+| ENDIF | 1 | |
+| ... whatever ... | | this line is processed |
+| ENDIF | | |
+
projects / cassiopeia.git / blobdiff