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primops: lazy evaluation of replaceStrings replacements

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The primop `builtins.replaceStrings` currently always strictly evaluates the
replacement strings, however time and space are wasted for their computation
if the corresponding pattern do not occur in the input string. This commit
makes the evaluation of the replacement strings lazy by deferring their
evaluation to when the corresponding pattern are matched and memoize the result
for efficient retrieval on subsequent matches.

The testcases for replaceStrings was updated to check for lazy evaluation
of the replacements. A note was also added in the release notes to
document the behavior change.
This commit is contained in:
polykernel 2023-05-25 00:37:00 -04:00
parent 6e4570234d
commit a382919d7d
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5 changed files with 17 additions and 14 deletions
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2
src/libexpr/tests/error_traces.cc
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@ -171,7 +171,7 @@ namespace nix {
hintfmt("value is %s while a string was expected", "an integer"),
hintfmt("while evaluating one of the strings to replace passed to builtins.replaceStrings"));
ASSERT_TRACE2("replaceStrings [ \"old\" ] [ true ] {}",
ASSERT_TRACE2("replaceStrings [ \"oo\" ] [ true ] \"foo\"",
TypeError,
hintfmt("value is %s while a string was expected", "a Boolean"),
hintfmt("while evaluating one of the replacement strings passed to builtins.replaceStrings"));