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fix(3p/nix): Use a proper pointer in Env to carry with-attrs

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This eliminates the value-smuggling that would trip up the GC.

Change-Id: I8057df78cf0bf6bea9faf1b44233aa9820ae44f5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1504
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: tazjin <mail@tazj.in>
This commit is contained in:
Kane York 2020-07-31 15:12:11 -07:00 • committed by kanepyork
parent dc4c0bad65
commit 770034042a
2 changed files with 9 additions and 5 deletions
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13
third_party/nix/src/libexpr/eval.cc vendored
View file

@ -600,10 +600,13 @@ inline Value* EvalState::lookupVar(Env* env, const ExprVar& var, bool noEval) {
if (noEval) { if (noEval) {
return nullptr; return nullptr;
} }
if (!env->withAttrsExpr) {
CHECK(false) << "HasWithExpr evaluated twice";
}
Value* v = allocValue(); Value* v = allocValue();
// TODO(kanepyork): Here's the other end of the cast smuggle. evalAttrs(*env->up, env->withAttrsExpr, *v);
evalAttrs(*env->up, reinterpret_cast<Expr*>(env->values[0]), *v);
env->values[0] = v; env->values[0] = v;
env->withAttrsExpr = nullptr;
env->type = Env::HasWithAttrs; env->type = Env::HasWithAttrs;
} }
Bindings::iterator j = env->values[0]->attrs->find(var.name); Bindings::iterator j = env->values[0]->attrs->find(var.name);
@ -1179,9 +1182,9 @@ void ExprWith::eval(EvalState& state, Env& env, Value& v) {
env2.up = &env; env2.up = &env;
env2.prevWith = prevWith; env2.prevWith = prevWith;
env2.type = Env::HasWithExpr; env2.type = Env::HasWithExpr;
// TODO(kanepyork): Figure out what's going on here. `Expr* attrs` is not /* placeholder for result of attrs */
// layout-compatible with Value*. env2.values[0] = nullptr;
env2.values[0] = reinterpret_cast<Value*>(attrs); env2.withAttrsExpr = this->attrs;
body->eval(state, env2, v); body->eval(state, env2, v);
} }

1
third_party/nix/src/libexpr/eval.hh vendored
View file

@ -42,6 +42,7 @@ struct Env : public gc {
unsigned short prevWith : 14; // nr of levels up to next `with' environment unsigned short prevWith : 14; // nr of levels up to next `with' environment
enum { Plain = 0, HasWithExpr, HasWithAttrs } type : 2; enum { Plain = 0, HasWithExpr, HasWithAttrs } type : 2;
std::vector<Value*, traceable_allocator<Value*>> values; std::vector<Value*, traceable_allocator<Value*>> values;
Expr* withAttrsExpr = nullptr;
}; };
Value& mkString(Value& v, const std::string& s, Value& mkString(Value& v, const std::string& s,