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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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10
src/libexpr/eval.cc
View file

@ -278,7 +278,7 @@ EvalState::EvalState(const Strings & _searchPath, ref<Store> store)
/* Initialise the Nix expression search path. */
Strings paths = parseNixPath(getEnv("NIX_PATH", ""));
for (auto & i : _searchPath) addToSearchPath(i, true);
for (auto & i : _searchPath) addToSearchPath(i);
for (auto & i : paths) addToSearchPath(i);
addToSearchPath("nix=" + settings.nixDataDir + "/nix/corepkgs");
@ -301,11 +301,15 @@ Path EvalState::checkSourcePath(const Path & path_)
if (!restricted) return path_;
/* Resolve symlinks. */
debug(format("checking access to ‘%s’") % path_);
Path path = canonPath(path_, true);
for (auto & i : searchPath)
if (path == i.second || isInDir(path, i.second))
for (auto & i : searchPath) {
auto r = resolveSearchPathElem(i);
if (!r.first) continue;
if (path == r.second || isInDir(path, r.second))
return path;
}
/* To support import-from-derivation, allow access to anything in
the store. FIXME: only allow access to paths that have been

10
src/libexpr/eval.hh
View file

@ -56,7 +56,8 @@ typedef std::map<Path, Path> SrcToStore;
std::ostream & operator << (std::ostream & str, const Value & v);
typedef list<std::pair<string, Path> > SearchPath;
typedef std::pair<std::string, std::string> SearchPathElem;
typedef std::list<SearchPathElem> SearchPath;
/* Initialise the Boehm GC, if applicable. */
@ -98,12 +99,14 @@ private:
SearchPath searchPath;
std::map<std::string, std::pair<bool, std::string>> searchPathResolved;
public:
EvalState(const Strings & _searchPath, ref<Store> store);
~EvalState();
void addToSearchPath(const string & s, bool warn = false);
void addToSearchPath(const string & s);
Path checkSourcePath(const Path & path);
@ -125,6 +128,9 @@ public:
Path findFile(const string & path);
Path findFile(SearchPath & searchPath, const string & path, const Pos & pos = noPos);
/* If the specified search path element is a URI, download it. */
std::pair<bool, std::string> resolveSearchPathElem(const SearchPathElem & elem);
/* Evaluate an expression to normal form, storing the result in
value `v'. */
void eval(Expr * e, Value & v);

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;
}
}

23
src/libexpr/primops.cc
View file

@ -778,7 +778,6 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
SearchPath searchPath;
PathSet context;
for (unsigned int n = 0; n < args[0]->listSize(); ++n) {
Value & v2(*args[0]->listElems()[n]);
state.forceAttrs(v2, pos);
@ -791,21 +790,23 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
i = v2.attrs->find(state.symbols.create("path"));
if (i == v2.attrs->end())
throw EvalError(format("attribute ‘path’ missing, at %1%") % pos);
string path = state.coerceToPath(pos, *i->value, context);
searchPath.push_back(std::pair<string, Path>(prefix, state.checkSourcePath(path)));
PathSet context;
string path = state.coerceToString(pos, *i->value, context, false, false);
try {
state.realiseContext(context);
} catch (InvalidPathError & e) {
throw EvalError(format("cannot find ‘%1%’, since path ‘%2%’ is not valid, at %3%")
% path % e.path % pos);
}
searchPath.emplace_back(prefix, path);
}
string path = state.forceStringNoCtx(*args[1], pos);
try {
state.realiseContext(context);
} catch (InvalidPathError & e) {
throw EvalError(format("cannot find ‘%1%’, since path ‘%2%’ is not valid, at %3%")
% path % e.path % pos);
}
mkPath(v, state.findFile(searchPath, path, pos).c_str());
mkPath(v, state.checkSourcePath(state.findFile(searchPath, path, pos)).c_str());
}
/* Read a directory (without . or ..) */

6
tests/tarball.sh
View file

@ -21,3 +21,9 @@ nix-build -o $TMPDIR/result file://$tarball
nix-build -o $TMPDIR/result '<foo>' -I foo=file://$tarball
nix-build -o $TMPDIR/result -E "import (fetchTarball file://$tarball)"
nix-instantiate --eval -E '1 + 2' -I fnord=file://no-such-tarball.tar.xz
nix-instantiate --eval -E 'with <fnord/xyzzy>; 1 + 2' -I fnord=file://no-such-tarball.tar.xz
(! nix-instantiate --eval -E '<fnord/xyzzy> 1' -I fnord=file://no-such-tarball.tar.xz)
nix-instantiate --eval -E '<fnord/config.nix>' -I fnord=file://no-such-tarball.tar.xz -I fnord=.