| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | Configure Internals |
| 2 | =================== |
| 3 | |
| 4 | [ note: this file uses markdown for formatting ] |
| 5 | |
| 6 | Intro |
| 7 | ----- |
| 8 | |
| 9 | This is a collection of notes that are hopefully of interest to those |
| 10 | who decide to dive into Configure and what it does. This is a living |
| 11 | document and anyone is encouraged to add to it and submit changes. |
| 12 | There's no claim for this document to be complete at any time, but it |
| 13 | will hopefully reach such a point in time. |
| 14 | |
| 15 | |
| 16 | ---------------------------------------------------------------------- |
| 17 | |
| 18 | Parsing build.info files, processing conditions |
| 19 | ----------------------------------------------- |
| 20 | |
| 21 | Processing conditions in build.info files is done with the help of a |
| 22 | condition stack that tell if a build.info should be processed or if it |
| 23 | should just be skipped over. The possible states of the stack top are |
| 24 | expressed in the following comment from Configure: |
| 25 | |
| 26 | # The top item of this stack has the following values |
| 27 | # -2 positive already run and we found ELSE (following ELSIF should fail) |
| 28 | # -1 positive already run (skip until ENDIF) |
| 29 | # 0 negatives so far (if we're at a condition, check it) |
| 30 | # 1 last was positive (don't skip lines until next ELSE, ELSIF or ENDIF) |
| 31 | # 2 positive ELSE (following ELSIF should fail) |
| 32 | |
| 33 | Ground rule is that non-condition lines are skipped over if the |
| 34 | stack top is > 0. Condition lines (IF, ELSIF, ELSE and ENDIF |
| 35 | statements) need to be processed either way to keep track of the skip |
| 36 | stack states, so they are a little more intricate. |
| 37 | |
| 38 | Instead of trying to describe in words, here are some example of what |
| 39 | the skip stack should look like after each line is processed: |
| 40 | |
| 41 | Example 1: |
| 42 | |
| 43 | | IF[1] | 1 | | |
| 44 | | ... whatever ... | | this line is processed | |
| 45 | | IF[1] | 1 1 | | |
| 46 | | ... whatever ... | | this line is processed | |
| 47 | | ELSIF[1] | 1 -1 | | |
| 48 | | ... whatever ... | | this line is skipped over | |
| 49 | | ELSE | 1 -2 | | |
| 50 | | ... whatever ... | | this line is skipped over | |
| 51 | | ENDIF | 1 | | |
| 52 | | ... whatever ... | | this line is processed | |
| 53 | | ELSIF[1] | -1 | | |
| 54 | | ... whatever ... | | this line is skipped over | |
| 55 | | IF[1] | -1 -1 | | |
| 56 | | ... whatever ... | | this line is skipped over | |
| 57 | | ELSIF[1] | -1 -1 | | |
| 58 | | ... whatever ... | | this line is skipped over | |
| 59 | | ELSE | -1 -2 | | |
| 60 | | ... whatever ... | | this line is skipped over | |
| 61 | | ENDIF | -1 | | |
| 62 | | ... whatever ... | | this line is skipped over | |
| 63 | | ENDIF | | | |
| 64 | |
| 65 | Example 2: |
| 66 | |
| 67 | | IF[0] | 0 | | |
| 68 | | ... whatever ... | | this line is skipped over | |
| 69 | | IF[1] | 0 -1 | | |
| 70 | | ... whatever ... | | this line is skipped over | |
| 71 | | ELSIF[1] | 0 -1 | | |
| 72 | | ... whatever ... | | this line is skipped over | |
| 73 | | ELSE | 0 -2 | | |
| 74 | | ... whatever ... | | this line is skipped over | |
| 75 | | ENDIF | 0 | | |
| 76 | | ... whatever ... | | this line is skipped over | |
| 77 | | ELSIF[1] | 1 | | |
| 78 | | ... whatever ... | | this line is processed | |
| 79 | | IF[1] | 1 1 | | |
| 80 | | ... whatever ... | | this line is processed | |
| 81 | | ELSIF[1] | 1 -1 | | |
| 82 | | ... whatever ... | | this line is skipped over | |
| 83 | | ELSE | 1 -2 | | |
| 84 | | ... whatever ... | | this line is skipped over | |
| 85 | | ENDIF | 1 | | |
| 86 | | ... whatever ... | | this line is processed | |
| 87 | | ENDIF | | | |
| 88 | |
| 89 | Example 3: |
| 90 | |
| 91 | | IF[0] | 0 | | |
| 92 | | ... whatever ... | | this line is skipped over | |
| 93 | | IF[0] | 0 -1 | | |
| 94 | | ... whatever ... | | this line is skipped over | |
| 95 | | ELSIF[1] | 0 -1 | | |
| 96 | | ... whatever ... | | this line is skipped over | |
| 97 | | ELSE | 0 -2 | | |
| 98 | | ... whatever ... | | this line is skipped over | |
| 99 | | ENDIF | 0 | | |
| 100 | | ... whatever ... | | this line is skipped over | |
| 101 | | ELSIF[1] | 1 | | |
| 102 | | ... whatever ... | | this line is processed | |
| 103 | | IF[0] | 1 0 | | |
| 104 | | ... whatever ... | | this line is skipped over | |
| 105 | | ELSIF[1] | 1 1 | | |
| 106 | | ... whatever ... | | this line is processed | |
| 107 | | ELSE | 1 -2 | | |
| 108 | | ... whatever ... | | this line is skipped over | |
| 109 | | ENDIF | 1 | | |
| 110 | | ... whatever ... | | this line is processed | |
| 111 | | ENDIF | | | |
| 112 | |
| 113 | Example 4: |
| 114 | |
| 115 | | IF[0] | 0 | | |
| 116 | | ... whatever ... | | this line is skipped over | |
| 117 | | IF[0] | 0 -1 | | |
| 118 | | ... whatever ... | | this line is skipped over | |
| 119 | | ELSIF[0] | 0 -1 | | |
| 120 | | ... whatever ... | | this line is skipped over | |
| 121 | | ELSE | 0 -2 | | |
| 122 | | ... whatever ... | | this line is skipped over | |
| 123 | | ENDIF | 0 | | |
| 124 | | ... whatever ... | | this line is skipped over | |
| 125 | | ELSIF[1] | 1 | | |
| 126 | | ... whatever ... | | this line is processed | |
| 127 | | IF[0] | 1 0 | | |
| 128 | | ... whatever ... | | this line is skipped over | |
| 129 | | ELSIF[0] | 1 0 | | |
| 130 | | ... whatever ... | | this line is skipped over | |
| 131 | | ELSE | 1 2 | | |
| 132 | | ... whatever ... | | this line is processed | |
| 133 | | ENDIF | 1 | | |
| 134 | | ... whatever ... | | this line is processed | |
| 135 | | ENDIF | | | |
| 136 | |