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Make the search path lazier with non-fatal errors

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Thus, -I / $NIX_PATH entries are now downloaded only when they are
needed for evaluation. An error to download an entry is a non-fatal
warning (just like non-existant paths).

This does change the semantics of builtins.nixPath, which now returns
the original, rather than resulting path. E.g., before we had

  [ { path = "/nix/store/hgm3yxf1lrrwa3z14zpqaj5p9vs0qklk-nixexprs.tar.xz"; prefix = "nixpkgs"; } ... ]

but now

  [ { path = "https://nixos.org/channels/nixos-16.03/nixexprs.tar.xz"; prefix = "nixpkgs"; } ... ]

Fixes #792.
This commit is contained in:
Eelco Dolstra 2016-04-14 15:32:24 +02:00
parent fc6a032989
commit 363f37d084
5 changed files with 75 additions and 34 deletions
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60
src/libexpr/parser.y
View file

@ -600,7 +600,7 @@ Expr * EvalState::parseExprFromString(const string & s, const Path & basePath)
}
void EvalState::addToSearchPath(const string & s, bool warn)
void EvalState::addToSearchPath(const string & s)
{
size_t pos = s.find('=');
string prefix;
@ -612,16 +612,7 @@ void EvalState::addToSearchPath(const string & s, bool warn)
path = string(s, pos + 1);
}
if (isUri(path))
path = makeDownloader()->downloadCached(store, path, true);
path = absPath(path);
if (pathExists(path)) {
debug(format("adding path ‘%1%’ to the search path") % path);
/* Resolve symlinks in the path to support restricted mode. */
searchPath.push_back(std::pair<string, Path>(prefix, canonPath(path, true)));
} else if (warn)
printMsg(lvlError, format("warning: Nix search path entry ‘%1%’ does not exist, ignoring") % path);
searchPath.emplace_back(prefix, path);
}
@ -634,17 +625,19 @@ Path EvalState::findFile(const string & path)
Path EvalState::findFile(SearchPath & searchPath, const string & path, const Pos & pos)
{
for (auto & i : searchPath) {
assert(!isUri(i.second));
Path res;
std::string suffix;
if (i.first.empty())
res = i.second + "/" + path;
suffix = "/" + path;
else {
if (path.compare(0, i.first.size(), i.first) != 0 ||
(path.size() > i.first.size() && path[i.first.size()] != '/'))
auto s = i.first.size();
if (path.compare(0, s, i.first) != 0 ||
(path.size() > s && path[s] != '/'))
continue;
res = i.second +
(path.size() == i.first.size() ? "" : "/" + string(path, i.first.size()));
suffix = path.size() == s ? "" : "/" + string(path, s);
}
auto r = resolveSearchPathElem(i);
if (!r.first) continue;
Path res = r.second + suffix;
if (pathExists(res)) return canonPath(res);
}
format f = format(
@ -655,4 +648,35 @@ Path EvalState::findFile(SearchPath & searchPath, const string & path, const Pos
}
std::pair<bool, std::string> EvalState::resolveSearchPathElem(const SearchPathElem & elem)
{
auto i = searchPathResolved.find(elem.second);
if (i != searchPathResolved.end()) return i->second;
std::pair<bool, std::string> res;
if (isUri(elem.second)) {
try {
res = { true, makeDownloader()->downloadCached(store, elem.second, true) };
} catch (DownloadError & e) {
printMsg(lvlError, format("warning: Nix search path entry ‘%1%’ cannot be downloaded, ignoring") % elem.second);
res = { false, "" };
}
} else {
auto path = absPath(elem.second);
if (pathExists(path))
res = { true, path };
else {
printMsg(lvlError, format("warning: Nix search path entry ‘%1%’ does not exist, ignoring") % elem.second);
res = { false, "" };
}
}
debug(format("resolved search path element ‘%s’ to ‘%s’") % elem.second % res.second);
searchPathResolved[elem.second] = res;
return res;
}
}