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5 commits

Author SHA1 Message Date
polykernel
a382919d7d
primops: lazy evaluation of replaceStrings replacements
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.
2023-05-25 18:35:23 -04:00
Tuomas Tynkkynen
77e9e1ed91 libexpr: Fix prim_replaceStrings() to work on an empty source string
Otherwise, running e.g.

nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'

would just hang in an infinite loop.

Found by afl-fuzz.

First attempt of this was reverted in e2d71bd186 because it caused
another infinite loop, which is fixed now and a test added.
2018-02-26 19:49:13 +02:00
Eelco Dolstra
e2d71bd186
Revert "libexpr: Fix prim_replaceStrings() to work on an empty source string"
This reverts commit 4ea9707591.

It causes an infinite loop in Nixpkgs evaluation,
e.g. "nix-instantiate -A hello" hung.

PR #1886.
2018-02-21 15:35:28 +01:00
Tuomas Tynkkynen
4ea9707591 libexpr: Fix prim_replaceStrings() to work on an empty source string
Otherwise, running e.g.

nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'

would just hang in an infinite loop.

Found by afl-fuzz.
2018-02-19 23:20:26 +02:00
Eelco Dolstra
d6d5885c15 Add replaceStrings primop
This is a generalisation of replaceChars in Nixpkgs.
2015-07-24 15:32:24 +02:00