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Brad King authored
A common idiom in CMake-based build systems is to have custom commands that generate files not listed explicitly as outputs so that these files do not have to be newer than the inputs. The file modification times of such "byproducts" are updated only when their content changes. Then other build rules can depend on the byproducts explicitly so that their dependents rebuild when the content of the original byproducts really does change. This "undeclared byproduct" approach is necessary for Makefile, VS, and Xcode build tools because if a byproduct were listed as an output of a rule then the rule would always rerun when the input is newer than the byproduct but the byproduct may never be updated. Ninja solves this problem by offering a 'restat' feature to check whether an output was really modified after running a rule and tracking the fact that it is up to date separately from its timestamp. However, Ninja also stats all dependencies up f...
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