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mamake: add 4 "automatic variables" to reduce Mamfile redundancy
This is another step towards making the build system easier to
maintain. The following special MAM variables are now set and
updated automatically. They are inspired by similar automatic
variables in make implementations, but since mamake is different,
so are these variables.
${@} is the name of the rule currently being made.
${<} is the name of the prerequisite rule (make...done or prev)
that was *last* processed within the current rule.
${^} is a space-separated list of names of all the current rule's
previously processed prerequisites.
${?} is a space-separate list of the current rule's previously
processed prerequisites that have been updated by a shell action
during the current mamake run. Prequisites that were already up to
date, or prerequisites that do not contain a shell action, are not
included.
*/*/Mamfile:
- Use the automatic variables to eliminate repetitive values (the
single-source-of-truth principle). Many rules are now identical
except for their rule name and prerequisites, showing the need
for another new mamake feature that would make it possible to
further reduce redundancy -- to come soon.
src/cmd/INIT/mamake.c:
- For ${?} we need to keep track of whether a rule was updated by a
shell action during this run. Add a RULE_updated flag for this.
- Declare global pointers to the automatic variable nodes.
- Amend duplicate() to make it easy to reallocate a string using
realloc(), with an optimisation that avoids allocating memory for
the empty string; this works by declaring a global constant
'empty' pointer to an empty string and comparing value pointers
to that before freeing them. The realloc version is called
reduplicate().
- Amend search() to return the pointer to the node (root), not the
node name (root->name), if a value was given. Only one call in
rule() used the root->name return value, so that's easy to fix.
- main(): Create the global automatic variable nodes while
initialising the global pointers to them, which is made possible
by the previous change. Set their initial values to the
unallocated empty string. Their ->value pointers are never NULL.
- Add a tweak to substitute() to allow '?' as the first character
of a variable name without interpreting it as an operator; ${?}
is not possible without it.
- In make(), when processing 'exec', expand variables immediately
upon collecting each line of script and don't wait with expanding
them until 'done' when executing the script. This avoids getting
confusing values of ${<}, ${^} and ${?}.
- make(): For 'make' and 'prev', save, set and restore the
automatic variables as required by their expected function.
- Saving and restoring pointers on the C stack is needed to make
nested rules do the right thing; nesting corresponds with
make() call recursion, so that's easy.
- The initialisation of the nodes in main() makes it possible to
address the global node pointers directly without any repeated
search() calls.
- The new reduplicate() function makes it convenient to
free/reallocate values.- Loading branch information
