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hashDerivationModulo: Generalize for multiple fixed ouputs per drv

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See documentattion in header and comments in implementation for details.

This is actually done in preparation for floating ca derivations, not
multi-output fixed ca derivations, but the distinction doesn't yet
mattter.

Thanks @cole-h for finding and fixing a bunch of typos.
This commit is contained in:
John Ericson 2020-03-19 00:37:57 -04:00 • committed by John Ericson
parent ef74fafc03
commit f1cf3ab870
4 changed files with 100 additions and 35 deletions
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33
src/libstore/derivations.hh
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@ -5,6 +5,7 @@
#include "store-api.hh"
#include <map>
#include <variant>
namespace nix {
@ -87,10 +88,38 @@ Derivation readDerivation(const Store & store, const Path & drvPath);
// FIXME: remove
bool isDerivation(const string & fileName);
Hash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs);
typedef std::variant<
Hash, // regular DRV normalized hash
std::map<std::string, Hash> // known CA drv's output hashes
> DrvHashModulo;
/* Returns hashes with the details of fixed-output subderivations
expunged.
A fixed-output derivation is a derivation whose outputs have a
specified content hash and hash algorithm. (Currently they must have
exactly one output (`out'), which is specified using the `outputHash'
and `outputHashAlgo' attributes, but the algorithm doesn't assume
this). We don't want changes to such derivations to propagate upwards
through the dependency graph, changing output paths everywhere.
For instance, if we change the url in a call to the `fetchurl'
function, we do not want to rebuild everything depending on it (after
all, (the hash of) the file being downloaded is unchanged). So the
*output paths* should not change. On the other hand, the *derivation
paths* should change to reflect the new dependency graph.
For fixed output derivations, this returns a map from the names of
each output to hashes unique up to the outputs' contents.
For regular derivations, it returns a single hash of the derivation
ATerm, after subderivations have been likewise expunged from that
derivation.
*/
DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool maskOutputs);
/* Memoisation of hashDerivationModulo(). */
typedef std::map<StorePath, Hash> DrvHashes;
typedef std::map<StorePath, DrvHashModulo> DrvHashes;
extern DrvHashes drvHashes; // FIXME: global, not thread-safe