forked from lix-project/lix
Merge pull request #9658 from pennae/env-diet
reduce the size of Env by one pointer
(cherry picked from commit 83f5622545a2fc31eb7e7d5105f64ed6dd3058b3)
Change-Id: I5636290526d0165cfc61aee1e7a5b94db4a26cef
This commit is contained in:
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cd326a2aa4
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7
doc/manual/rl-next/env-size-reduction.md
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7
doc/manual/rl-next/env-size-reduction.md
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---
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synopsis: Reduce eval memory usage and wall time
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prs: 9658
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---
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Reduce the size of the `Env` struct used in the evaluator by a pointer, or 8 bytes on most modern machines.
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This reduces memory usage during eval by around 2% and wall time by around 3%.
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31
doc/manual/rl-next/with-error-reporting.md
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31
doc/manual/rl-next/with-error-reporting.md
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---
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synopsis: Better error reporting for `with` expressions
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prs: 9658
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---
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`with` expressions using non-attrset values to resolve variables are now reported with proper positions.
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Previously an incorrect `with` expression would report no position at all, making it hard to determine where the error originated:
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```
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nix-repl> with 1; a
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error:
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… <borked>
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at «none»:0: (source not available)
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error: value is an integer while a set was expected
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```
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Now position information is preserved and reported as with most other errors:
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```
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nix-repl> with 1; a
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error:
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… while evaluating the first subexpression of a with expression
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at «string»:1:1:
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1| with 1; a
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| ^
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error: value is an integer while a set was expected
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```
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@ -109,7 +109,7 @@ NixRepl::NixRepl(const SearchPath & searchPath, nix::ref<Store> store, ref<EvalS
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: AbstractNixRepl(state)
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, debugTraceIndex(0)
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, getValues(getValues)
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, staticEnv(new StaticEnv(false, state->staticBaseEnv.get()))
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, staticEnv(new StaticEnv(nullptr, state->staticBaseEnv.get()))
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, historyFile(getDataDir() + "/nix/repl-history")
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{
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}
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@ -73,8 +73,6 @@ Env & EvalState::allocEnv(size_t size)
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#endif
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env = (Env *) allocBytes(sizeof(Env) + size * sizeof(Value *));
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env->type = Env::Plain;
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/* We assume that env->values has been cleared by the allocator; maybeThunk() and lookupVar fromWith expect this. */
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return *env;
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@ -519,7 +519,7 @@ EvalState::EvalState(
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, env1AllocCache(std::allocate_shared<void *>(traceable_allocator<void *>(), nullptr))
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#endif
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, baseEnv(allocEnv(128))
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, staticBaseEnv{std::make_shared<StaticEnv>(false, nullptr)}
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, staticBaseEnv{std::make_shared<StaticEnv>(nullptr, nullptr)}
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{
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countCalls = getEnv("NIX_COUNT_CALLS").value_or("0") != "0";
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@ -788,7 +788,7 @@ void printStaticEnvBindings(const SymbolTable & st, const StaticEnv & se)
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// just for the current level of Env, not the whole chain.
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void printWithBindings(const SymbolTable & st, const Env & env)
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{
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if (env.type == Env::HasWithAttrs) {
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if (!env.values[0]->isThunk()) {
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std::cout << "with: ";
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std::cout << ANSI_MAGENTA;
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Bindings::iterator j = env.values[0]->attrs->begin();
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@ -842,7 +842,7 @@ void mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const En
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if (env.up && se.up) {
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mapStaticEnvBindings(st, *se.up, *env.up, vm);
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if (env.type == Env::HasWithAttrs) {
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if (!env.values[0]->isThunk()) {
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// add 'with' bindings.
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Bindings::iterator j = env.values[0]->attrs->begin();
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while (j != env.values[0]->attrs->end()) {
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@ -980,22 +980,23 @@ inline Value * EvalState::lookupVar(Env * env, const ExprVar & var, bool noEval)
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if (!var.fromWith) return env->values[var.displ];
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// This early exit defeats the `maybeThunk` optimization for variables from `with`,
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// The added complexity of handling this appears to be similarly in cost, or
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// the cases where applicable were insignificant in the first place.
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if (noEval) return nullptr;
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auto * fromWith = var.fromWith;
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while (1) {
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if (env->type == Env::HasWithExpr) {
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if (noEval) return 0;
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Value * v = allocValue();
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evalAttrs(*env->up, (Expr *) env->values[0], *v, noPos, "<borked>");
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env->values[0] = v;
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env->type = Env::HasWithAttrs;
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}
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forceAttrs(*env->values[0], fromWith->pos, "while evaluating the first subexpression of a with expression");
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Bindings::iterator j = env->values[0]->attrs->find(var.name);
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if (j != env->values[0]->attrs->end()) {
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if (countCalls) attrSelects[j->pos]++;
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return j->value;
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}
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if (!env->prevWith)
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if (!fromWith->parentWith)
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error("undefined variable '%1%'", symbols[var.name]).atPos(var.pos).withFrame(*env, var).debugThrow<UndefinedVarError>();
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for (size_t l = env->prevWith; l; --l, env = env->up) ;
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for (size_t l = fromWith->prevWith; l; --l, env = env->up) ;
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fromWith = fromWith->parentWith;
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}
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}
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@ -1854,9 +1855,7 @@ void ExprWith::eval(EvalState & state, Env & env, Value & v)
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{
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Env & env2(state.allocEnv(1));
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env2.up = &env;
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env2.prevWith = prevWith;
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env2.type = Env::HasWithExpr;
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env2.values[0] = (Value *) attrs;
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env2.values[0] = attrs->maybeThunk(state, env);
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body->eval(state, env2, v);
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}
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@ -115,11 +115,6 @@ struct Constant
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struct Env
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{
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Env * up;
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/**
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* Number of of levels up to next `with` environment
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*/
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unsigned short prevWith:14;
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enum { Plain = 0, HasWithExpr, HasWithAttrs } type:2;
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Value * values[0];
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};
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@ -333,6 +333,8 @@ void ExprVar::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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if (es.debugRepl)
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es.exprEnvs.insert(std::make_pair(this, env));
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fromWith = nullptr;
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/* Check whether the variable appears in the environment. If so,
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set its level and displacement. */
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const StaticEnv * curEnv;
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@ -344,7 +346,6 @@ void ExprVar::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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} else {
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auto i = curEnv->find(name);
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if (i != curEnv->vars.end()) {
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fromWith = false;
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this->level = level;
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displ = i->second;
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return;
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@ -360,7 +361,8 @@ void ExprVar::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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.msg = hintfmt("undefined variable '%1%'", es.symbols[name]),
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.errPos = es.positions[pos]
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});
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fromWith = true;
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for (auto * e = env.get(); e && !fromWith; e = e->up)
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fromWith = e->isWith;
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this->level = withLevel;
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}
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@ -393,7 +395,7 @@ void ExprAttrs::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv>
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es.exprEnvs.insert(std::make_pair(this, env));
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if (recursive) {
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auto newEnv = std::make_shared<StaticEnv>(false, env.get(), recursive ? attrs.size() : 0);
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auto newEnv = std::make_shared<StaticEnv>(nullptr, env.get(), recursive ? attrs.size() : 0);
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Displacement displ = 0;
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for (auto & i : attrs)
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@ -435,7 +437,7 @@ void ExprLambda::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv>
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es.exprEnvs.insert(std::make_pair(this, env));
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auto newEnv = std::make_shared<StaticEnv>(
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false, env.get(),
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nullptr, env.get(),
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(hasFormals() ? formals->formals.size() : 0) +
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(!arg ? 0 : 1));
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@ -471,7 +473,7 @@ void ExprLet::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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if (es.debugRepl)
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es.exprEnvs.insert(std::make_pair(this, env));
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auto newEnv = std::make_shared<StaticEnv>(false, env.get(), attrs->attrs.size());
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auto newEnv = std::make_shared<StaticEnv>(nullptr, env.get(), attrs->attrs.size());
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Displacement displ = 0;
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for (auto & i : attrs->attrs)
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@ -490,6 +492,10 @@ void ExprWith::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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if (es.debugRepl)
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es.exprEnvs.insert(std::make_pair(this, env));
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parentWith = nullptr;
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for (auto * e = env.get(); e && !parentWith; e = e->up)
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parentWith = e->isWith;
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/* Does this `with' have an enclosing `with'? If so, record its
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level so that `lookupVar' can look up variables in the previous
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`with' if this one doesn't contain the desired attribute. */
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@ -506,7 +512,7 @@ void ExprWith::bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> &
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es.exprEnvs.insert(std::make_pair(this, env));
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attrs->bindVars(es, env);
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auto newEnv = std::make_shared<StaticEnv>(true, env.get());
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auto newEnv = std::make_shared<StaticEnv>(this, env.get());
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body->bindVars(es, newEnv);
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}
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@ -139,6 +139,7 @@ std::ostream & operator << (std::ostream & str, const Pos & pos);
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struct Env;
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struct Value;
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class EvalState;
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struct ExprWith;
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struct StaticEnv;
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@ -221,8 +222,11 @@ struct ExprVar : Expr
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Symbol name;
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/* Whether the variable comes from an environment (e.g. a rec, let
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or function argument) or from a "with". */
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bool fromWith;
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or function argument) or from a "with".
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`nullptr`: Not from a `with`.
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Valid pointer: the nearest, innermost `with` expression to query first. */
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ExprWith * fromWith;
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/* In the former case, the value is obtained by going `level`
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levels up from the current environment and getting the
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@ -380,6 +384,7 @@ struct ExprWith : Expr
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PosIdx pos;
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Expr * attrs, * body;
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size_t prevWith;
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ExprWith * parentWith;
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ExprWith(const PosIdx & pos, Expr * attrs, Expr * body) : pos(pos), attrs(attrs), body(body) { };
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PosIdx getPos() const override { return pos; }
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COMMON_METHODS
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@ -473,14 +478,14 @@ extern ExprBlackHole eBlackHole;
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runtime. */
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struct StaticEnv
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{
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bool isWith;
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ExprWith * isWith;
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const StaticEnv * up;
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// Note: these must be in sorted order.
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typedef std::vector<std::pair<Symbol, Displacement>> Vars;
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Vars vars;
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StaticEnv(bool isWith, const StaticEnv * up, size_t expectedSize = 0) : isWith(isWith), up(up) {
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StaticEnv(ExprWith * isWith, const StaticEnv * up, size_t expectedSize = 0) : isWith(isWith), up(up) {
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vars.reserve(expectedSize);
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};
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@ -233,7 +233,7 @@ static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * v
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Env * env = &state.allocEnv(vScope->attrs->size());
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env->up = &state.baseEnv;
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auto staticEnv = std::make_shared<StaticEnv>(false, state.staticBaseEnv.get(), vScope->attrs->size());
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auto staticEnv = std::make_shared<StaticEnv>(nullptr, state.staticBaseEnv.get(), vScope->attrs->size());
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unsigned int displ = 0;
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for (auto & attr : *vScope->attrs) {
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