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Set regex_constants::match_continuous for quicker search

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match_continuous limits the search to the current start position,
instead of searching the entire file.

On libc++, this improves performance dramatically:

$ time /nix/store/70ai68dfm6xbzwn26j5n4li9di52ylia-nix-3.0pre20200728_c159f48/bin/nix print-dev-env >/dev/null
/nix/store/70ai68dfm6xbzwn26j5n4li9di52ylia-nix-3.0pre20200728_c159f48/bin/ni  2.39s user 0.19s system 64% cpu 4.032 total
$ time /nix/store/cwjfxxlp83zln4mfyy1d2dbsx7f6s962-nix-3.0pre20200728_dirty/bin/nix print-dev-env >/dev/null
/nix/store/cwjfxxlp83zln4mfyy1d2dbsx7f6s962-nix-3.0pre20200728_dirty/bin/nix   0.09s user 0.05s system 65% cpu 0.204 total

Fixes #3874
This commit is contained in:
Matthew Bauer 2020-07-29 00:57:20 -05:00
parent c159f48a39
commit fa8515d7ec
1 changed files with 4 additions and 4 deletions
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8
src/nix/develop.cc
View file

@ -68,22 +68,22 @@ BuildEnvironment readEnvironment(const Path & path)
std::smatch match;
if (std::regex_search(pos, file.cend(), match, declareRegex)) {
if (std::regex_search(pos, file.cend(), match, declareRegex, std::regex_constants::match_continuous)) {
pos = match[0].second;
exported.insert(match[1]);
}
else if (std::regex_search(pos, file.cend(), match, varRegex)) {
else if (std::regex_search(pos, file.cend(), match, varRegex, std::regex_constants::match_continuous)) {
pos = match[0].second;
res.env.insert({match[1], Var { .exported = exported.count(match[1]) > 0, .value = match[2] }});
}
else if (std::regex_search(pos, file.cend(), match, assocArrayRegex)) {
else if (std::regex_search(pos, file.cend(), match, assocArrayRegex, std::regex_constants::match_continuous)) {
pos = match[0].second;
res.env.insert({match[1], Var { .associative = true, .value = match[2] }});
}
else if (std::regex_search(pos, file.cend(), match, functionRegex)) {
else if (std::regex_search(pos, file.cend(), match, functionRegex, std::regex_constants::match_continuous)) {
res.bashFunctions = std::string(pos, file.cend());
break;
}