08c53923db
determination (e.g., finding the header files dependencies of a C
file) in Nix low-level builds automatically.
For instance, in the function `compileC' in make/lib/default.nix, we
find the header file dependencies of C file `main' as follows:
localIncludes =
dependencyClosure {
scanner = file:
import (findIncludes {
inherit file;
});
startSet = [main];
};
The function works by "growing" the set of dependencies, starting
with the set `startSet', and calling the function `scanner' for each
file to get its dependencies (which should yield a list of strings
representing relative paths). For instance, when `scanner' is
called on a file `foo.c' that includes the line
#include "../bar/fnord.h"
then `scanner' should yield ["../bar/fnord.h"]. This list of
dependencies is absolutised relative to the including file and added
to the set of dependencies. The process continues until no more
dependencies are found (hence its a closure).
`dependencyClosure' yields a list that contains in alternation a
dependency, and its relative path to the directory of the start
file, e.g.,
[ /bla/bla/foo.c
"foo.c"
/bla/bar/fnord.h
"../bar/fnord.h"
]
These relative paths are necessary for the builder that compiles
foo.c to reconstruct the relative directory structure expected by
foo.c.
The advantage of `dependencyClosure' over the old approach (using
the impure `__currentTime') is that it's completely pure, and more
efficient because it only rescans for dependencies (i.e., by
building the derivations yielded by `scanner') if sources have
actually changed. The old approach rescanned every time.
75 lines
1.9 KiB
Bash
75 lines
1.9 KiB
Bash
. $stdenv/setup
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mainName=$(basename $main | cut -c34-)
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echo "compiling \`$mainName'..."
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# Turn $localIncludes into an array.
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localIncludes=($localIncludes)
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# Determine how many `..' levels appear in the header file references.
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# E.g., if there is some reference `../../foo.h', then we have to
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# insert two extra levels in the directory structure, so that `a.c' is
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# stored at `dotdot/dotdot/a.c', and a reference from it to
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# `../../foo.h' resolves to `dotdot/dotdot/../../foo.h' == `foo.h'.
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n=0
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maxDepth=0
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for ((n = 0; n < ${#localIncludes[*]}; n += 2)); do
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target=${localIncludes[$((n + 1))]}
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# Split the target name into path components using some IFS magic.
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savedIFS="$IFS"
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IFS=/
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components=($target)
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depth=0
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for ((m = 0; m < ${#components[*]}; m++)); do
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c=${components[m]}
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if test "$c" = ".."; then
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depth=$((depth + 1))
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fi
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done
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IFS="$savedIFS"
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if test $depth -gt $maxDepth; then
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maxDepth=$depth;
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fi
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done
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# Create the extra levels in the directory hierarchy.
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prefix=
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for ((n = 0; n < maxDepth; n++)); do
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prefix="dotdot/$prefix"
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done
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# Create symlinks to the header files.
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for ((n = 0; n < ${#localIncludes[*]}; n += 2)); do
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source=${localIncludes[n]}
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target=${localIncludes[$((n + 1))]}
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# Create missing directories. We use IFS magic to split the path
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# into path components.
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savedIFS="$IFS"
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IFS=/
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components=($prefix$target)
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fullPath=(.)
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for ((m = 0; m < ${#components[*]} - 1; m++)); do
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fullPath=("${fullPath[@]}" ${components[m]})
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if ! test -d "${fullPath[*]}"; then
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mkdir "${fullPath[*]}"
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fi
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done
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IFS="$savedIFS"
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ln -sf $source $prefix$target
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done
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# Create a symlink to the main file.
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if ! test "$(readlink $prefix$mainName)" = $main; then
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ln -s $main $prefix$mainName
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fi
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mkdir $out
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test "$prefix" && cd $prefix
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ls -l
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gcc -Wall $cFlags -c $mainName -o $out/$mainName.o
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