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Add builtins.getContext.

Browse source 
This can be very helpful when debugging, as well as enabling complex
black magic like surgically removing a single dependency from a
string's context.
This commit is contained in:
Shea Levy 2019-01-13 12:43:46 -05:00
parent 087be7281a
commit 1d757292d0
No known key found for this signature in database
GPG key ID: 5C0BD6957D86FE27
5 changed files with 158 additions and 38 deletions
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3
src/libexpr/eval.hh
View file

@ -316,6 +316,9 @@ private:
/* Return a string representing the type of the value `v'. */
string showType(const Value & v);
/* Decode a context string ‘!<name>!<path>’ into a pair <path,
name>. */
std::pair<string, string> decodeContext(const string & s);
/* If `path' refers to a directory, then append "/default.nix". */
Path resolveExprPath(Path path);

38
src/libexpr/primops.cc
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@ -1780,41 +1780,6 @@ static void prim_stringLength(EvalState & state, const Pos & pos, Value * * args
}
static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
string s = state.coerceToString(pos, *args[0], context);
mkString(v, s, PathSet());
}
static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
state.forceString(*args[0], context, pos);
mkBool(v, !context.empty());
}
/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
builder without causing the derivation to be built (for instance,
in the derivation that builds NARs in nix-push, when doing
source-only deployment). This primop marks the string context so
that builtins.derivation adds the path to drv.inputSrcs rather than
drv.inputDrvs. */
static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
string s = state.coerceToString(pos, *args[0], context);
PathSet context2;
for (auto & p : context)
context2.insert(p.at(0) == '=' ? string(p, 1) : p);
mkString(v, s, context2);
}
/* Return the cryptographic hash of a string in base-16. */
static void prim_hashString(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
@ -2285,9 +2250,6 @@ void EvalState::createBaseEnv()
addPrimOp("toString", 1, prim_toString);
addPrimOp("__substring", 3, prim_substring);
addPrimOp("__stringLength", 1, prim_stringLength);
addPrimOp("__hasContext", 1, prim_hasContext);
addPrimOp("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
addPrimOp("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
addPrimOp("__hashString", 2, prim_hashString);
addPrimOp("__match", 2, prim_match);
addPrimOp("__split", 2, prim_split);

132
src/libexpr/primops/context.cc Normal file
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@ -0,0 +1,132 @@
#include "primops.hh"
#include "eval-inline.hh"
namespace nix {
static void prim_unsafeDiscardStringContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
string s = state.coerceToString(pos, *args[0], context);
mkString(v, s, PathSet());
}
static RegisterPrimOp r1("__unsafeDiscardStringContext", 1, prim_unsafeDiscardStringContext);
static void prim_hasContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
state.forceString(*args[0], context, pos);
mkBool(v, !context.empty());
}
static RegisterPrimOp r2("__hasContext", 1, prim_hasContext);
/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
builder without causing the derivation to be built (for instance,
in the derivation that builds NARs in nix-push, when doing
source-only deployment). This primop marks the string context so
that builtins.derivation adds the path to drv.inputSrcs rather than
drv.inputDrvs. */
static void prim_unsafeDiscardOutputDependency(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
PathSet context;
string s = state.coerceToString(pos, *args[0], context);
PathSet context2;
for (auto & p : context)
context2.insert(p.at(0) == '=' ? string(p, 1) : p);
mkString(v, s, context2);
}
static RegisterPrimOp r3("__unsafeDiscardOutputDependency", 1, prim_unsafeDiscardOutputDependency);
/* Extract the context of a string as a structured Nix value.
The context is represented as an attribute set whose keys are the
paths in the context set and whose values are attribute sets with
the following keys:
path: True if the relevant path is in the context as a plain store
path (i.e. the kind of context you get when interpolating
a Nix path (e.g. ./.) into a string). False if missing.
allOutputs: True if the relevant path is a derivation and it is
in the context as a drv file with all of its outputs
(i.e. the kind of context you get when referencing
.drvPath of some derivation). False if missing.
outputs: If a non-empty list, the relevant path is a derivation
and the provided outputs are referenced in the context
(i.e. the kind of context you get when referencing
.outPath of some derivation). Empty list if missing.
Note that for a given path any combination of the above attributes
may be present, but at least one must be set to something other
than the default.
*/
static void prim_getContext(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
struct ContextInfo {
bool path = false;
bool allOutputs = false;
Strings outputs;
};
PathSet context;
state.forceString(*args[0], context, pos);
auto contextInfos = std::map<Path, ContextInfo>();
for (const auto & p : context) {
Path drv;
string output;
const Path * path = &p;
if (p.at(0) == '=') {
drv = string(p, 1);
path = &drv;
} else if (p.at(0) == '!') {
std::pair<string, string> ctx = decodeContext(p);
drv = ctx.first;
output = ctx.second;
path = &drv;
}
auto isPath = drv.empty();
auto isAllOutputs = (!drv.empty()) && output.empty();
auto iter = contextInfos.find(*path);
if (iter == contextInfos.end()) {
contextInfos.emplace(*path, ContextInfo{isPath, isAllOutputs, output.empty() ? Strings{} : Strings{std::move(output)}});
} else {
if (isPath)
iter->second.path = true;
else if (isAllOutputs)
iter->second.allOutputs = true;
else
iter->second.outputs.emplace_back(std::move(output));
}
}
state.mkAttrs(v, contextInfos.size());
auto sPath = state.symbols.create("path");
auto sAllOutputs = state.symbols.create("allOutputs");
for (const auto & info : contextInfos) {
auto & infoVal = *state.allocAttr(v, state.symbols.create(info.first));
state.mkAttrs(infoVal, 3);
if (info.second.path)
mkBool(*state.allocAttr(infoVal, sPath), true);
if (info.second.allOutputs)
mkBool(*state.allocAttr(infoVal, sAllOutputs), true);
if (!info.second.outputs.empty()) {
auto & outputsVal = *state.allocAttr(infoVal, state.sOutputs);
state.mkList(outputsVal, info.second.outputs.size());
size_t i = 0;
for (const auto & output : info.second.outputs) {
mkString(*(outputsVal.listElems()[i++] = state.allocValue()), output);
}
}
infoVal.attrs->sort();
}
v.attrs->sort();
}
static RegisterPrimOp r4("__getContext", 1, prim_getContext);
}

1
tests/lang/eval-okay-context-introspection.exp Normal file
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@ -0,0 +1 @@
true

22
tests/lang/eval-okay-context-introspection.nix Normal file
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@ -0,0 +1,22 @@
let
drv = derivation {
name = "fail";
builder = "/bin/false";
system = "x86_64-linux";
outputs = [ "out" "foo" ];
};
path = "${./eval-okay-context-introspection.nix}";
desired-context = {
"${builtins.unsafeDiscardStringContext path}" = {
path = true;
};
"${builtins.unsafeDiscardStringContext drv.drvPath}" = {
outputs = [ "foo" "out" ];
allOutputs = true;
};
};
legit-context = "${path}${drv.outPath}${drv.foo.outPath}${drv.drvPath}";
in builtins.getContext legit-context == desired-context