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Merge pull request #14061 from xokdvium/k-way-update

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libexpr: Preparation for more k-way updates of attribute sets (NFC)
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Sergei Zimmerman 2025-09-25 00:29:54 +03:00 • committed by GitHub
commit 05279f2ba0
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5 changed files with 107 additions and 54 deletions
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38
src/libexpr/eval.cc
View file

@ -1866,12 +1866,8 @@ void ExprOpImpl::eval(EvalState & state, Env & env, Value & v)
|| state.evalBool(env, e2, pos, "in the right operand of the IMPL (->) operator"));
}
void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
void ExprOpUpdate::eval(EvalState & state, Value & v, Value & v1, Value & v2)
{
Value v1, v2;
state.evalAttrs(env, e1, v1, pos, "in the left operand of the update (//) operator");
state.evalAttrs(env, e2, v2, pos, "in the right operand of the update (//) operator");
state.nrOpUpdates++;
const Bindings & bindings1 = *v1.attrs();
@ -1945,6 +1941,38 @@ void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
state.nrOpUpdateValuesCopied += v.attrs()->size();
}
void ExprOpUpdate::eval(EvalState & state, Env & env, Value & v)
{
UpdateQueue q;
evalForUpdate(state, env, q);
v.mkAttrs(&Bindings::emptyBindings);
for (auto & rhs : std::views::reverse(q)) {
/* Remember that queue is sorted rightmost attrset first. */
eval(state, /*v=*/v, /*v1=*/v, /*v2=*/rhs);
}
}
void Expr::evalForUpdate(EvalState & state, Env & env, UpdateQueue & q, std::string_view errorCtx)
{
Value v;
state.evalAttrs(env, this, v, getPos(), errorCtx);
q.push_back(v);
}
void ExprOpUpdate::evalForUpdate(EvalState & state, Env & env, UpdateQueue & q)
{
/* Output rightmost attrset first to the merge queue as the one
with the most priority. */
e2->evalForUpdate(state, env, q, "in the right operand of the update (//) operator");
e1->evalForUpdate(state, env, q, "in the left operand of the update (//) operator");
}
void ExprOpUpdate::evalForUpdate(EvalState & state, Env & env, UpdateQueue & q, std::string_view errorCtx)
{
evalForUpdate(state, env, q);
}
void ExprOpConcatLists::eval(EvalState & state, Env & env, Value & v)
{
Value v1;

16
src/libexpr/include/nix/expr/gc-small-vector.hh
View file

@ -26,4 +26,20 @@ using SmallValueVector = SmallVector<Value *, nItems>;
template<size_t nItems>
using SmallTemporaryValueVector = SmallVector<Value, nItems>;
/**
* For functions where we do not expect deep recursion, we can use a sizable
* part of the stack a free allocation space.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t nonRecursiveStackReservation = 128;
/**
* Functions that maybe applied to self-similar inputs, such as concatMap on a
* tree, should reserve a smaller part of the stack for allocation.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t conservativeStackReservation = 16;
} // namespace nix

87
src/libexpr/include/nix/expr/nixexpr.hh
View file

@ -4,6 +4,7 @@
#include <map>
#include <vector>
#include "nix/expr/gc-small-vector.hh"
#include "nix/expr/value.hh"
#include "nix/expr/symbol-table.hh"
#include "nix/expr/eval-error.hh"
@ -80,6 +81,8 @@ typedef std::vector<AttrName> AttrPath;
std::string showAttrPath(const SymbolTable & symbols, const AttrPath & attrPath);
using UpdateQueue = SmallTemporaryValueVector<conservativeStackReservation>;
/* Abstract syntax of Nix expressions. */
struct Expr
@ -110,6 +113,14 @@ struct Expr
* of thunks allocated.
*/
virtual Value * maybeThunk(EvalState & state, Env & env);
/**
* Only called when performing an attrset update: `//` or similar.
* Instead of writing to a Value &, this function writes to an UpdateQueue.
* This allows the expression to perform multiple updates in a delayed manner, gathering up all the updates before
* applying them.
*/
virtual void evalForUpdate(EvalState & state, Env & env, UpdateQueue & q, std::string_view errorCtx);
virtual void setName(Symbol name);
virtual void setDocComment(DocComment docComment) {};
@ -574,36 +585,39 @@ struct ExprOpNot : Expr
COMMON_METHODS
};
#define MakeBinOp(name, s) \
struct name : Expr \
{ \
PosIdx pos; \
Expr *e1, *e2; \
name(Expr * e1, Expr * e2) \
: e1(e1) \
, e2(e2) {}; \
name(const PosIdx & pos, Expr * e1, Expr * e2) \
: pos(pos) \
, e1(e1) \
, e2(e2) {}; \
void show(const SymbolTable & symbols, std::ostream & str) const override \
{ \
str << "("; \
e1->show(symbols, str); \
str << " " s " "; \
e2->show(symbols, str); \
str << ")"; \
} \
void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override \
{ \
e1->bindVars(es, env); \
e2->bindVars(es, env); \
} \
void eval(EvalState & state, Env & env, Value & v) override; \
PosIdx getPos() const override \
{ \
return pos; \
} \
#define MakeBinOpMembers(name, s) \
PosIdx pos; \
Expr *e1, *e2; \
name(Expr * e1, Expr * e2) \
: e1(e1) \
, e2(e2){}; \
name(const PosIdx & pos, Expr * e1, Expr * e2) \
: pos(pos) \
, e1(e1) \
, e2(e2){}; \
void show(const SymbolTable & symbols, std::ostream & str) const override \
{ \
str << "("; \
e1->show(symbols, str); \
str << " " s " "; \
e2->show(symbols, str); \
str << ")"; \
} \
void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override \
{ \
e1->bindVars(es, env); \
e2->bindVars(es, env); \
} \
void eval(EvalState & state, Env & env, Value & v) override; \
PosIdx getPos() const override \
{ \
return pos; \
}
#define MakeBinOp(name, s) \
struct name : Expr \
{ \
MakeBinOpMembers(name, s) \
}
MakeBinOp(ExprOpEq, "==");
@ -611,9 +625,20 @@ MakeBinOp(ExprOpNEq, "!=");
MakeBinOp(ExprOpAnd, "&&");
MakeBinOp(ExprOpOr, "||");
MakeBinOp(ExprOpImpl, "->");
MakeBinOp(ExprOpUpdate, "//");
MakeBinOp(ExprOpConcatLists, "++");
struct ExprOpUpdate : Expr
{
private:
/** Special case for merging of two attrsets. */
void eval(EvalState & state, Value & v, Value & v1, Value & v2);
void evalForUpdate(EvalState & state, Env & env, UpdateQueue & q);
public:
MakeBinOpMembers(ExprOpUpdate, "//");
virtual void evalForUpdate(EvalState & state, Env & env, UpdateQueue & q, std::string_view errorCtx) override;
};
struct ExprConcatStrings : Expr
{
PosIdx pos;

16
src/libexpr/include/nix/expr/primops.hh
View file

@ -8,22 +8,6 @@
namespace nix {
/**
* For functions where we do not expect deep recursion, we can use a sizable
* part of the stack a free allocation space.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t nonRecursiveStackReservation = 128;
/**
* Functions that maybe applied to self-similar inputs, such as concatMap on a
* tree, should reserve a smaller part of the stack for allocation.
*
* Note: this is expected to be multiplied by sizeof(Value), or about 24 bytes.
*/
constexpr size_t conservativeStackReservation = 16;
struct RegisterPrimOp
{
typedef std::vector<PrimOp> PrimOps;

4
tests/functional/lang/eval-fail-recursion.err.exp
View file

@ -1,9 +1,9 @@
error:
… in the right operand of the update (//) operator
at /pwd/lang/eval-fail-recursion.nix:2:11:
at /pwd/lang/eval-fail-recursion.nix:2:14:
1| let
2| a = { } // a;
| ^
| ^
3| in
error: infinite recursion encountered