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Start documenting Configure internals
This is a living document, everyone is encouraged to add to it. Implementation details as well as broader implementation philosophy has a place here. I'm starting with documentation of the how conditions in build.info files are treated. Reviewed-by: Rich Salz <[email protected]>
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| Configure Internals | ||
| =================== | ||
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| [ note: this file uses markdown for formatting ] | ||
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| Intro | ||
| ----- | ||
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| 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. | ||
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| ---------------------------------------------------------------------- | ||
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| Parsing build.info files, processing conditions | ||
| ----------------------------------------------- | ||
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| 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: | ||
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| # 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) | ||
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| 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. | ||
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| Instead of trying to describe in words, here are some example of what | ||
| the skip stack should look like after each line is processed: | ||
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| Example 1: | ||
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| | 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 | | | | ||
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| Example 2: | ||
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| | 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 | | | | ||
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| Example 3: | ||
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| | 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 | | | | ||
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| Example 4: | ||
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| | 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 | | | | ||
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