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|
package eval
// eval implementations for each Expr type.
// Methods are filled in incrementally as test slices are implemented.
// The four literal evals return the Value boxed when the node was built. See
// the ExprInt/ExprString/... declarations for why that box exists.
func (e *ExprInt) eval(_ *EvalState, _ *Env) (Value, error) {
return e.val, nil
}
func (e *ExprFloat) eval(_ *EvalState, _ *Env) (Value, error) {
return e.val, nil
}
func (e *ExprString) eval(_ *EvalState, _ *Env) (Value, error) {
return e.val, nil
}
func (e *ExprPath) eval(_ *EvalState, _ *Env) (Value, error) {
return e.val, nil
}
func (e *ExprVar) eval(s *EvalState, env *Env) (Value, error) {
// Walk up `level` env frames.
cur := env
for i := uint32(0); i < e.Level; i++ {
if cur.Up == nil {
return nil, evalErrorf("%senv chain too short for var %s (level=%d)", s.posStr(e.Pos), s.Symbols.Str(e.Name), e.Level)
}
cur = cur.Up
}
if !e.FromWith {
if int(e.Displ) >= len(cur.Values) {
return nil, evalErrorf("%sdispl %d out of range (env size %d) for var %s",
s.posStr(e.Pos), e.Displ, len(cur.Values), s.Symbols.Str(e.Name))
}
v := cur.Values[e.Displ]
if err := s.forceValue(&v, e.Pos); err != nil {
return nil, err
}
cur.Values[e.Displ] = v
return v, nil
}
// `with` lookup: walk the with-chain looking for the attribute.
// Mirrors C++ lookupVar's fromWith->prevWith / fromWith->parentWith walk.
// Forces the with-env slot in place (matching C++ forceAttrs on env->values[0]).
for i := -1; ; i++ {
if err := s.forceValue(&cur.Values[0], e.Pos); err != nil {
return nil, err
}
attrs, ok := cur.Values[0].(VAttrs)
if !ok {
return nil, evalErrorf("%swith expression evaluated to %s, not a set", s.posStr(e.Pos), valueType(cur.Values[0]))
}
attr := attrs.Bindings.Get(e.Name)
if attr != nil {
if err := s.forceValue(&attr.Value, e.Pos); err != nil {
return nil, err
}
return attr.Value, nil
}
// Not found; advance to next enclosing with if any.
if i+1 >= len(e.WithChain) {
return nil, evalErrorf("%sundefined variable '%s'", s.posStr(e.Pos), s.Symbols.Str(e.Name))
}
steps := e.WithChain[i+1]
for j := uint32(0); j < steps; j++ {
cur = cur.Up
}
}
}
func (e *ExprIf) eval(s *EvalState, env *Env) (Value, error) {
cond, err := e.Cond.eval(s, env)
if err != nil {
return nil, err
}
b, err := s.forceBool(&cond, e.Pos)
if err != nil {
return nil, err
}
if b {
return e.Then.eval(s, env)
}
return e.Else.eval(s, env)
}
func (e *ExprAssert) eval(s *EvalState, env *Env) (Value, error) {
cond, err := e.Cond.eval(s, env)
if err != nil {
return nil, err
}
b, err := s.forceBool(&cond, e.Pos)
if err != nil {
return nil, err
}
if !b {
return nil, evalErrorf("%sassertion failed", s.posStr(e.Pos))
}
return e.Body.eval(s, env)
}
func (e *ExprOpNot) eval(s *EvalState, env *Env) (Value, error) {
v, err := e.E.eval(s, env)
if err != nil {
return nil, err
}
b, err := s.forceBool(&v, e.Pos)
if err != nil {
return nil, err
}
if b {
return VFalseSingleton, nil
}
return VTrueSingleton, nil
}
func (e *ExprOpAnd) eval(s *EvalState, env *Env) (Value, error) {
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
b1, err := s.forceBool(&v1, e.Pos)
if err != nil {
return nil, err
}
if !b1 {
return VFalseSingleton, nil
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
b2, err := s.forceBool(&v2, e.Pos)
if err != nil {
return nil, err
}
if b2 {
return VTrueSingleton, nil
}
return VFalseSingleton, nil
}
func (e *ExprOpOr) eval(s *EvalState, env *Env) (Value, error) {
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
b1, err := s.forceBool(&v1, e.Pos)
if err != nil {
return nil, err
}
if b1 {
return VTrueSingleton, nil
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
b2, err := s.forceBool(&v2, e.Pos)
if err != nil {
return nil, err
}
if b2 {
return VTrueSingleton, nil
}
return VFalseSingleton, nil
}
func (e *ExprOpImpl) eval(s *EvalState, env *Env) (Value, error) {
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
b1, err := s.forceBool(&v1, NoPosIdx)
if err != nil {
return nil, err
}
if !b1 {
return VTrueSingleton, nil
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
b2, err := s.forceBool(&v2, NoPosIdx)
if err != nil {
return nil, err
}
if b2 {
return VTrueSingleton, nil
}
return VFalseSingleton, nil
}
func (e *ExprOpEq) eval(s *EvalState, env *Env) (Value, error) {
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
eq, err := s.eqValues(v1, v2, e.Pos)
if err != nil {
return nil, err
}
if eq {
return VTrueSingleton, nil
}
return VFalseSingleton, nil
}
func (e *ExprOpNEq) eval(s *EvalState, env *Env) (Value, error) {
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
eq, err := s.eqValues(v1, v2, e.Pos)
if err != nil {
return nil, err
}
if !eq {
return VTrueSingleton, nil
}
return VFalseSingleton, nil
}
func (e *ExprOpUpdate) eval(s *EvalState, env *Env) (Value, error) {
// Counted here and not in mergeBindings, because C++ increments at the top
// of updateAttrs (eval.cc:1352) *before* its own empty-operand
// short-circuit returns. gonix's short-circuit is one level down, inside
// mergeBindings, so counting there would silently drop every
// `attrs // optionalAttrs cond {…}` — which the note on mergeBindings says
// is a large fraction of all // evaluations. The undercount would have
// looked like gonix evaluating fewer updates for the same result.
s.Stats.NrOpUpdates++
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
b1, err := s.forceAttrs(&v1, e.Pos, "in the left operand of the update (//) operator")
if err != nil {
return nil, err
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
b2, err := s.forceAttrs(&v2, e.Pos, "in the right operand of the update (//) operator")
if err != nil {
return nil, err
}
return VAttrs{Bindings: mergeBindings(s, b1, b2)}, nil
}
// mergeBindings returns b1 // b2 (b2 wins on conflicts). Both must be sorted.
//
// Ported from C++ EvalState::updateAttrs (libexpr/eval.cc:1350), with one
// deliberate difference: the merge is *deferred*. The result is an overlay
// over the two operands (see Bindings), and the sorted copy C++ builds here
// is built only if something wants the whole set — and then in place, so the
// set keeps its identity. On legosi 84% of merged sets are never traversed by
// anything except a further //, which an overlay does not traverse either;
// see "A lazy //" in OPTIMIZATION.md for the measurement this rests on.
//
// NOTE: when one side is empty the other side is returned *verbatim*, so the
// result may alias an input rather than being a fresh copy. C++ does the same,
// and it is safe for the same reason: a published *Bindings is never
// *observably* mutated — an overlay materialising changes its representation,
// not its contents. Sharing is already pervasive — EmptyBindings is a global,
// and every VAttrs copy shares its Bindings pointer. It is also actively
// useful, because eqValues short-circuits on Bindings pointer identity
// (coerce.go), as do the cycle-detection maps in the printer and deepForce.
//
// This is not a micro-optimisation: `attrs // optionalAttrs cond {…}` is
// everywhere in nixpkgs and the NixOS module system, so the empty cases are a
// large fraction of all // evaluations.
func mergeBindings(s *EvalState, b1, b2 *Bindings) *Bindings {
n1, n2 := b1.Len(), b2.Len()
if n1 == 0 {
return b2
}
if n2 == 0 {
return b1
}
// Counted as if allocated, because C++ does allocate here:
// buildBindings(size1 + size2) goes through allocBindings, which counts
// the reservation (attr-set.cc:21). Counting only when an overlay
// materialises would make nrAttrsets/nrAttrsInAttrsets drop by exactly
// the win, and the comparison against Lix — which is how the // path was
// shown to do no extra work — would stop meaning anything.
s.Stats.NrAttrsets++
s.Stats.NrAttrsInAttrsets += uint64(n1 + n2)
return newOverlay(b1, b2)
}
func (e *ExprOpConcatLists) eval(s *EvalState, env *Env) (Value, error) {
// Before the empty-operand short-circuit below, matching C++
// ExprOpConcatLists::eval, which increments as its first statement
// (eval-expr.cc:357) and only then returns the other operand verbatim.
s.Stats.NrListConcats++
v1, err := e.E1.eval(s, env)
if err != nil {
return nil, err
}
l1, err := s.forceList(&v1, e.Pos, "in the left operand of the list concatenation (++) operator")
if err != nil {
return nil, err
}
v2, err := e.E2.eval(s, env)
if err != nil {
return nil, err
}
l2, err := s.forceList(&v2, e.Pos, "in the right operand of the list concatenation (++) operator")
if err != nil {
return nil, err
}
// C++ ExprOpConcatLists::eval (eval-expr.cc:370) returns the other operand
// *itself* when one side is empty, rather than a fresh list wrapping the
// same elements. Keeping the value preserves pointer identity, which
// eqValues short-circuits on — the same reasoning as mergeBindings above.
if len(l1) == 0 {
return v2, nil
}
if len(l2) == 0 {
return v1, nil
}
combined := make([]Value, len(l1)+len(l2))
copy(combined, l1)
copy(combined[len(l1):], l2)
return newList(s, combined), nil
}
func (e *ExprConcatStrings) eval(s *EvalState, env *Env) (Value, error) {
return s.evalConcatStrings(e, env)
}
func (e *ExprList) eval(s *EvalState, env *Env) (Value, error) {
if len(e.Elems) == 0 {
return EmptyList, nil
}
elems := make([]Value, len(e.Elems))
for i := range e.Elems {
elems[i] = s.maybeThunk(&e.Elems[i], env)
}
return newList(s, elems), nil
}
func (e *ExprSet) eval(s *EvalState, env *Env) (Value, error) {
if e.Recursive {
return s.evalRecSet(e, env)
}
return s.evalNonRecSet(e, env)
}
func (s *EvalState) evalNonRecSet(e *ExprSet, env *Env) (Value, error) {
// Build inheritFrom env if needed.
var inheritEnv *Env
if len(e.InheritFrom) > 0 {
inheritEnv = newEnv(s, env, len(e.InheritFrom))
for i := range e.InheritFrom {
inheritEnv.Values[i] = s.maybeThunk(&e.InheritFrom[i], env)
}
}
cap := len(e.Attrs) + len(e.DynamicAttrs)
b := newBindings(s, cap)
for i := range e.Attrs {
ad := &e.Attrs[i]
thunkEnv := chooseEnv(ad.Kind, env, env, inheritEnv)
b.attrs = append(b.attrs, Attr{
Name: ad.Name,
Pos: ad.Pos,
Value: s.maybeThunk(&ad.Expr, thunkEnv),
})
}
b.Sort()
if err := s.evalDynamicAttrs(e.DynamicAttrs, env, b); err != nil {
return nil, err
}
return VAttrs{Bindings: b}, nil
}
func (s *EvalState) evalRecSet(e *ExprSet, env *Env) (Value, error) {
// Allocate the recursive env first, then fill it with thunks that close over it.
recEnv := newEnv(s, env, len(e.Attrs))
var inheritEnv *Env
if len(e.InheritFrom) > 0 {
inheritEnv = newEnv(s, recEnv, len(e.InheritFrom))
for i := range e.InheritFrom {
inheritEnv.Values[i] = s.maybeThunk(&e.InheritFrom[i], recEnv)
}
}
cap := len(e.Attrs) + len(e.DynamicAttrs)
b := newBindings(s, cap)
for i := range e.Attrs {
ad := &e.Attrs[i]
thunkEnv := chooseEnv(ad.Kind, recEnv, env, inheritEnv)
v := s.maybeThunk(&ad.Expr, thunkEnv)
recEnv.Values[i] = v
b.attrs = append(b.attrs, Attr{Name: ad.Name, Pos: ad.Pos, Value: v})
}
b.Sort()
if err := s.evalDynamicAttrs(e.DynamicAttrs, recEnv, b); err != nil {
return nil, err
}
return VAttrs{Bindings: b}, nil
}
// chooseEnv picks the environment for a binding based on its kind.
func chooseEnv(kind AttrDefKind, plain, inherited, inheritedFrom *Env) *Env {
switch kind {
case AttrDefPlain:
return plain
case AttrDefInherited:
return inherited
default: // AttrDefInheritedFrom
return inheritedFrom
}
}
func (s *EvalState) evalDynamicAttrs(dynAttrs []DynAttrDef, env *Env, b *Bindings) error {
// b arrives sorted, holding the statically known attrs. Everything this
// function appends goes after that prefix and is not in order, so we sort
// once at the end rather than after every insertion — re-sorting per attr
// makes a set of n dynamic attrs cost n sorts.
//
// The consequence is that the duplicate check cannot be a plain b.Get,
// which binary-searches and so would only be valid over the sorted prefix.
// It is split accordingly: binary search the prefix, linear scan the few
// attrs we have added ourselves.
if b.ov != nil {
// An overlay is a published set; appending to its (empty) attrs
// would silently shadow both operands. evalDynamicAttrs is only ever
// handed the set its caller has just built.
panic("evalDynamicAttrs on an overlay")
}
sortedPrefix := len(b.attrs)
appended := false
for k := range dynAttrs {
da := &dynAttrs[k]
nameV, err := da.NameExpr.eval(s, env)
if err != nil {
return err
}
if err := s.forceValue(&nameV, da.Pos); err != nil {
return err
}
// null nameExpr means skip this attr.
if _, isNull := nameV.(VNull); isNull {
continue
}
// C++ forceStringNoCtx (eval-expr.cc:172): the name becomes a Symbol,
// so it must already be a string and must carry no context. Coercing
// accepted `{ ${ { __toString = _: "a"; } } = 1; }`, which is a type
// error in C++.
nameStr, err := s.forceStringNoContext(&nameV, da.Pos,
"while evaluating the name of a dynamic attribute")
if err != nil {
return err
}
sym := s.Symbols.Create(nameStr)
duplicate := findAttr(b.attrs[:sortedPrefix], sym) != nil
for _, a := range b.attrs[sortedPrefix:] {
if a.Name == sym {
duplicate = true
break
}
}
if duplicate {
return evalErrorf("%sdynamic attribute '%s' already defined", s.posStr(da.Pos), nameStr)
}
b.attrs = append(b.attrs, Attr{
Name: sym,
Pos: da.Pos,
Value: s.maybeThunk(&dynAttrs[k].ValueExpr, env),
})
appended = true
}
if appended {
b.Sort()
}
return nil
}
func (e *ExprLet) eval(s *EvalState, env *Env) (Value, error) {
letEnv := newEnv(s, env, len(e.Attrs))
var inheritEnv *Env
if len(e.InheritFrom) > 0 {
inheritEnv = newEnv(s, letEnv, len(e.InheritFrom))
for i := range e.InheritFrom {
inheritEnv.Values[i] = s.maybeThunk(&e.InheritFrom[i], letEnv)
}
}
for i := range e.Attrs {
ad := &e.Attrs[i]
thunkEnv := chooseEnv(ad.Kind, letEnv, env, inheritEnv)
letEnv.Values[i] = s.maybeThunk(&ad.Expr, thunkEnv)
}
return e.Body.eval(s, letEnv)
}
func (e *ExprWith) eval(s *EvalState, env *Env) (Value, error) {
withEnv := newEnv(s, env, 1)
withEnv.Values[0] = s.maybeThunk(&e.Attrs, env)
return e.Body.eval(s, withEnv)
}
func (e *ExprSelect) eval(s *EvalState, env *Env) (Value, error) {
v, err := e.E.eval(s, env)
if err != nil {
return nil, err
}
for _, an := range e.AttrPath {
if err := s.forceValue(&v, an.Pos); err != nil {
return nil, err
}
attrs, ok := v.(VAttrs)
if !ok {
if e.Def != nil {
return e.Def.eval(s, env)
}
return nil, evalErrorf("%sexpected a set for attribute selection, got %s", s.posStr(an.Pos), valueType(v))
}
var sym Symbol
if an.Symbol != 0 {
sym = an.Symbol
} else {
nameV, err := an.Expr.eval(s, env)
if err != nil {
return nil, err
}
if err := s.forceValue(&nameV, an.Pos); err != nil {
return nil, err
}
// C++ getName -> forceStringNoCtx (eval.cc:174): an attribute
// name becomes a Symbol, so it must already be a string and
// carry no context.
ns, err := s.forceStringNoContext(&nameV, an.Pos,
"while evaluating an attribute name")
if err != nil {
return nil, err
}
sym = s.Symbols.Create(ns)
}
attr := attrs.Bindings.Get(sym)
if attr == nil {
if e.Def != nil {
return e.Def.eval(s, env)
}
return nil, evalErrorf("%sattribute '%s' missing", s.posStr(an.Pos), s.Symbols.Str(sym))
}
v = attr.Value
}
if err := s.forceValue(&v, e.Pos); err != nil {
return nil, err
}
return v, nil
}
func (e *ExprOpHasAttr) eval(s *EvalState, env *Env) (Value, error) {
v, err := e.E.eval(s, env)
if err != nil {
return nil, err
}
for _, an := range e.AttrPath {
if err := s.forceValue(&v, an.Pos); err != nil {
return nil, err
}
attrs, ok := v.(VAttrs)
if !ok {
return VFalseSingleton, nil
}
var sym Symbol
if an.Symbol != 0 {
sym = an.Symbol
} else {
nameV, err := an.Expr.eval(s, env)
if err != nil {
return nil, err
}
if err := s.forceValue(&nameV, an.Pos); err != nil {
return nil, err
}
// C++ getName -> forceStringNoCtx (eval.cc:174): an attribute
// name becomes a Symbol, so it must already be a string and
// carry no context.
ns, err := s.forceStringNoContext(&nameV, an.Pos,
"while evaluating an attribute name")
if err != nil {
return nil, err
}
sym = s.Symbols.Create(ns)
}
attr := attrs.Bindings.Get(sym)
if attr == nil {
return VFalseSingleton, nil
}
v = attr.Value
}
return VTrueSingleton, nil
}
func (e *ExprLambda) eval(_ *EvalState, env *Env) (Value, error) {
return &VLambda{Env: env, Fun: e}, nil
}
func (e *ExprCall) eval(s *EvalState, env *Env) (Value, error) {
fun, err := e.Fun.eval(s, env)
if err != nil {
return nil, err
}
// A fixed array rather than make([]Value, len(e.Args)): escape analysis
// already proves the slice does not escape (see "Taking the argument slice
// out of the primop calling convention" in OPTIMIZATION.md), but Go only
// stack-allocates a variable-length make up to 32 bytes — two Values — so
// every call with three or more arguments still went to the heap, 429K
// times per system evaluation. Four covers every applied lambda and primop
// call that is not a long curried chain.
var buf [4]Value
var args []Value
if len(e.Args) <= len(buf) {
args = buf[:len(e.Args)]
} else {
args = make([]Value, len(e.Args))
}
for i := range e.Args {
args[i] = s.maybeThunk(&e.Args[i], env)
}
return s.callFunction(fun, args, e.Pos)
}
func (e *ExprPos) eval(s *EvalState, _ *Env) (Value, error) {
return s.mkPos(e.Pos), nil
}
func (e *ExprInheritFrom) eval(s *EvalState, env *Env) (Value, error) {
if int(e.Displ) >= len(env.Values) {
return nil, evalErrorf("ExprInheritFrom: displ %d out of range", e.Displ)
}
v := env.Values[e.Displ]
if err := s.forceValue(&v, NoPosIdx); err != nil {
return nil, err
}
env.Values[e.Displ] = v
return v, nil
}
func (e *ExprDebugFrame) eval(s *EvalState, env *Env) (Value, error) {
return e.Inner.eval(s, env)
}
func (e *ExprBlackHole) eval(_ *EvalState, _ *Env) (Value, error) {
return nil, evalErrorf("infinite recursion encountered")
}
// --- Pattern.match implementations ---
func (p SimplePattern) match(s *EvalState, up *Env, arg Value, _ PosIdx) (*Env, error) {
env := newEnv(s, up, 1)
env.Values[0] = arg
return env, nil
}
func (p AttrsPattern) match(s *EvalState, up *Env, arg Value, lambdaPos PosIdx) (*Env, error) {
argCopy := arg
bindings, err := s.forceAttrs(&argCopy, lambdaPos, "while evaluating the value passed for the lambda argument")
if err != nil {
return nil, err
}
// C++ env layout: if there is a @ name binding, it occupies slot 0 and
// formals occupy slots 1..N. If there is no @ binding, formals are 0..N-1.
// This matches the displacement values assigned by the C++ parser's finalize.
offset := 0
size := len(p.Formals)
if p.Name != 0 {
offset = 1
size++
}
env := newEnv(s, up, size)
// Set the @ binding first (slot 0) so defaults that reference it are valid.
if p.Name != 0 {
env.Values[0] = arg
}
usedCount := 0
for i := range p.Formals {
f := &p.Formals[i]
attr := bindings.Get(f.Name)
if attr != nil {
env.Values[offset+i] = attr.Value
usedCount++
} else if f.HasDefault {
env.Values[offset+i] = s.maybeThunk(&f.Default, env)
} else {
return nil, evalErrorf("%sfunction called without required argument '%s'",
s.posStr(lambdaPos), s.Symbols.Str(f.Name))
}
}
if !p.Ellipsis && usedCount != bindings.Len() {
for _, attr := range bindings.All() {
found := false
for _, f := range p.Formals {
if f.Name == attr.Name {
found = true
break
}
}
if !found {
return nil, evalErrorf("%sfunction called with unexpected argument '%s'",
s.posStr(lambdaPos), s.Symbols.Str(attr.Name))
}
}
}
return env, nil
}
// ExprCallValue.eval defers a builtin function call with pre-captured values.
// The env argument is intentionally unused — all operands are already values.
// This mirrors the synthetic ExprCall thunks that C++ builtins construct.
func (e *ExprCallValue) eval(s *EvalState, _ *Env) (Value, error) {
return s.callFunction(e.Fn, e.args(), NoPosIdx)
}
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