Eelco Dolstra 08c53923db * A primitive operation `dependencyClosure' to do automatic dependency ... 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.		2005-08-14 12:38:47 +00:00
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default.nix	* A primitive operation `dependencyClosure' to do automatic dependency	2005-08-14 12:38:47 +00:00