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/// @file wasm-codec.cc -- codec wire-format encoder for the Nix AST.
/// See wasm-codec.hh for the format specification.
#include "lix/libexpr/wasm-codec.hh"
#include "lix/libexpr/nixexpr.hh"
#include "lix/libexpr/pos-table.hh"
#include "lix/libexpr/symbol-table.hh"
#include "lix/libutil/position.hh"
#include <cassert>
#include <string>
namespace nix::wasm_codec {
using std::string;
// ---------------------------------------------------------------------------
// Encoder visitor -- walks the Expr tree and produces codec wire bytes.
// ---------------------------------------------------------------------------
struct ASTEncoder : ExprVisitor
{
const SymbolTable & symbols;
const PosTable & positions;
string filePath; // file name for Pos::String origins (may be empty)
string result;
explicit ASTEncoder(
const SymbolTable & symbols, const PosTable & positions, std::string_view filePath = {}
)
: symbols(symbols)
, positions(positions)
, filePath(filePath)
{
}
// ---- helpers ----
string encSymbol(Symbol s) const
{
return encScalar(symbols[s]);
}
// Encode a PosIdx as a record {file, line, col}, or an empty record for noPos.
// Wire: "{" file-field line-field col-field "}" or "{}"
string encPos(PosIdx p) const
{
if (!p) {
return record("");
}
Pos resolved = positions[p];
if (!resolved) {
return record("");
}
auto origin = positions.originOf(p);
std::string posFile;
if (auto * cp = std::get_if<CheckedSourcePath>(&origin)) {
posFile = cp->to_string();
} else {
// Pos::String or Pos::Stdin origin — use the caller-supplied filePath.
posFile = filePath;
}
return record(
field("file", encScalar(posFile)) + field("line", encUint32(resolved.line))
+ field("col", encUint32(resolved.column))
);
}
string encAttrName(const AttrName & an)
{
if (an.symbol) {
return variant("sym", record(field("name", encSymbol(an.symbol)) + field("pos", encPos(an.pos))));
} else {
string inner = encode(*an.expr);
return variant("expr", record(field("expr", inner) + field("pos", encPos(an.pos))));
}
}
string encAttrPath(const AttrPath & ap)
{
string items;
for (const auto & an : ap) {
string enc = encAttrName(an);
items += listItem(enc);
}
return list(items);
}
string encAttrDef(const Symbol & name, const ExprAttrs::AttrDef & ad)
{
string kindStr;
switch (ad.kind) {
case ExprAttrs::AttrDef::Kind::Plain:
kindStr = "plain";
break;
case ExprAttrs::AttrDef::Kind::Inherited:
kindStr = "inherited";
break;
case ExprAttrs::AttrDef::Kind::InheritedFrom:
kindStr = "inheritedFrom";
break;
}
string inner = encode(*ad.e);
return record(
field("name", encSymbol(name)) + field("kind", encScalar(kindStr))
+ field("displ", encUint32(ad.displ)) + field("pos", encPos(ad.pos)) + field("expr", inner)
);
}
string encBindings(const ExprAttrs & ea)
{
// attrs list
string attrItems;
for (const auto & [name, ad] : ea.attrs) {
string enc = encAttrDef(name, ad);
attrItems += listItem(enc);
}
string fields = field("attrs", list(attrItems));
// dynamicAttrs list
string dynItems;
for (const auto & da : ea.dynamicAttrs) {
string nameEnc = encode(*da.nameExpr);
string valEnc = encode(*da.valueExpr);
string rec = record(
field("nameExpr", nameEnc) + field("valueExpr", valEnc) + field("pos", encPos(da.pos))
);
dynItems += listItem(rec);
}
fields += field("dynamicAttrs", list(dynItems));
// inheritFrom list
string inheritItems;
if (ea.inheritFromExprs) {
for (const auto & expr : *ea.inheritFromExprs) {
string enc = encode(*expr);
inheritItems += listItem(enc);
}
}
fields += field("inheritFrom", list(inheritItems));
return fields;
}
string encPattern(const Pattern & pat)
{
// SimplePattern
if (auto * sp = dynamic_cast<const SimplePattern *>(&pat)) {
return variant("simple", record(field("name", encSymbol(sp->name))));
}
// AttrsPattern
if (auto * ap = dynamic_cast<const AttrsPattern *>(&pat)) {
string formalItems;
for (const auto & f : ap->formals) {
string rec;
rec += field("name", encSymbol(f.name));
rec += field("hasDefault", encBool(f.def != nullptr));
rec += field("pos", encPos(f.pos));
if (f.def) {
rec += field("default", encode(*f.def));
}
formalItems += listItem(record(rec));
}
string fields;
fields += field("formals", list(formalItems));
fields += field("ellipsis", encBool(ap->ellipsis));
if (ap->name) {
fields += field("name", encSymbol(ap->name));
}
return variant("attrs", record(fields));
}
abort(); // unknown pattern type
}
// ---- main encode dispatch ----
string encode(Expr & e)
{
result.clear();
std::unique_ptr<Expr> dummy; // visitor needs a unique_ptr ref, but we won't move it
e.accept(*this, dummy);
return std::move(result);
}
// ---- visitor methods ----
void visit(ExprDebugFrame & e, std::unique_ptr<Expr> & ptr) override
{
result =
variant("ExprDebugFrame", record(field("pos", encPos(e.pos)) + field("inner", encode(*e.inner))));
}
void visit(ExprLiteral & e, std::unique_ptr<Expr> & ptr) override
{
// ExprLiteral is the base for ExprInt, ExprFloat, ExprString, ExprPath.
// Dispatch on the concrete subtype to encode appropriately.
const auto & v = e.literalValue();
switch (v.type()) {
case nInt:
result = variant(
"ExprInt", record(field("pos", encPos(e.pos)) + field("value", encInt64(v.integer().value)))
);
return;
case nFloat:
result = variant(
"ExprFloat", record(field("pos", encPos(e.pos)) + field("value", encFloat64(v.fpoint())))
);
return;
case nString:
result = variant(
"ExprString", record(field("pos", encPos(e.pos)) + field("value", encScalar(v.str())))
);
return;
case nPath: {
// Downcast to ExprPath to access the relative flag set by the parser.
const auto * ep = dynamic_cast<const ExprPath *>(&e);
bool isRelative = ep && ep->relative;
result = variant(
"ExprPath",
record(
field("pos", encPos(e.pos)) + field("value", encScalar(v.string().content->str()))
+ field("relative", encBool(isRelative))
)
);
return;
}
case nThunk:
case nBool:
case nNull:
case nAttrs:
case nList:
case nFunction:
case nExternal:
abort(); // ExprLiteral should only hold int/float/string/path
}
}
void visit(ExprVar & e, std::unique_ptr<Expr> & ptr) override
{
string fields;
fields += field("pos", encPos(e.pos));
fields += field("name", encSymbol(e.name));
fields += field("level", encUint32(e.level));
fields += field("displ", encUint32(e.displ));
fields += field("fromWith", encBool(e.fromWith != nullptr));
if (e.fromWith) {
// Encode the full with-chain as a list of prevWith step counts.
// Each entry is the number of env levels to go up from the current
// with-env to reach the next enclosing with-env.
// The Go evaluator walks this list when the attr is not found in
// the current with-scope, mirroring the C++ fromWith->parentWith chain.
string items;
for (auto * w = e.fromWith; w; w = w->parentWith) {
items += listItem(encUint32(static_cast<uint32_t>(w->prevWith)));
}
fields += field("withChain", list(items));
}
result = variant("ExprVar", record(fields));
}
void visit(ExprInheritFrom & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprInheritFrom", record(field("pos", encPos(e.pos)) + field("displ", encUint32(e.displ)))
);
}
void visit(ExprSelect & e, std::unique_ptr<Expr> & ptr) override
{
string fields;
fields += field("pos", encPos(e.pos));
fields += field("e", encode(*e.e));
fields += field("attrPath", encAttrPath(e.attrPath));
if (e.def) {
fields += field("def", encode(*e.def));
}
result = variant("ExprSelect", record(fields));
}
void visit(ExprOpHasAttr & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpHasAttr",
record(
field("pos", encPos(e.pos)) + field("e", encode(*e.e))
+ field("attrPath", encAttrPath(e.attrPath))
)
);
}
void visit(ExprSet & e, std::unique_ptr<Expr> & ptr) override
{
string fields;
fields += field("pos", encPos(e.pos));
fields += field("recursive", encBool(e.recursive));
fields += encBindings(e);
result = variant("ExprSet", record(fields));
}
void visit(ExprList & e, std::unique_ptr<Expr> & ptr) override
{
string items;
for (const auto & elem : e.elems) {
string enc = encode(*elem);
items += listItem(enc);
}
result = variant("ExprList", record(field("pos", encPos(e.pos)) + field("elems", list(items))));
}
void visit(ExprLambda & e, std::unique_ptr<Expr> & ptr) override
{
string fields;
fields += field("pos", encPos(e.pos));
if (e.name) {
fields += field("name", encSymbol(e.name));
}
fields += field("pattern", encPattern(*e.pattern));
fields += field("body", encode(*e.body));
result = variant("ExprLambda", record(fields));
}
void visit(ExprCall & e, std::unique_ptr<Expr> & ptr) override
{
string argItems;
for (const auto & arg : e.args) {
string enc = encode(*arg);
argItems += listItem(enc);
}
result = variant(
"ExprCall",
record(field("pos", encPos(e.pos)) + field("fun", encode(*e.fun)) + field("args", list(argItems)))
);
}
void visit(ExprLet & e, std::unique_ptr<Expr> & ptr) override
{
string fields;
fields += field("pos", encPos(e.pos));
fields += encBindings(e);
fields += field("body", encode(*e.body));
result = variant("ExprLet", record(fields));
}
void visit(ExprWith & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprWith",
record(
field("pos", encPos(e.pos)) + field("attrs", encode(*e.attrs))
+ field("body", encode(*e.body))
+ field("prevWith", encUint32(static_cast<uint32_t>(e.prevWith)))
)
);
}
void visit(ExprIf & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprIf",
record(
field("pos", encPos(e.pos)) + field("cond", encode(*e.cond)) + field("then", encode(*e.then))
+ field("else", encode(*e.else_))
)
);
}
void visit(ExprAssert & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprAssert",
record(
field("pos", encPos(e.pos)) + field("cond", encode(*e.cond)) + field("body", encode(*e.body))
)
);
}
void visit(ExprOpNot & e, std::unique_ptr<Expr> & ptr) override
{
result = variant("ExprOpNot", record(field("pos", encPos(e.pos)) + field("e", encode(*e.e))));
}
void visit(ExprOpEq & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpEq",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpNEq & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpNEq",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpAnd & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpAnd",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpOr & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpOr",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpImpl & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpImpl",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpUpdate & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpUpdate",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprOpConcatLists & e, std::unique_ptr<Expr> & ptr) override
{
result = variant(
"ExprOpConcatLists",
record(field("pos", encPos(e.pos)) + field("e1", encode(*e.e1)) + field("e2", encode(*e.e2)))
);
}
void visit(ExprConcatStrings & e, std::unique_ptr<Expr> & ptr) override
{
string items;
for (const auto & [partPos, part] : e.es) {
// Each part is a record {pos, expr} so the Go side can access
// the per-part position for type-mismatch error messages.
string rec = record(field("pos", encPos(partPos)) + field("expr", encode(*part)));
items += listItem(rec);
}
result = variant(
"ExprConcatStrings",
record(
field("pos", encPos(e.pos)) + field("isInterpolation", encBool(e.isInterpolation))
+ field("parts", list(items))
)
);
}
void visit(ExprPos & e, std::unique_ptr<Expr> & ptr) override
{
result = variant("ExprPos", record(field("pos", encPos(e.pos))));
}
void visit(ExprBlackHole & e, std::unique_ptr<Expr> & ptr) override
{
result = variant("ExprBlackHole", record(field("pos", encPos(e.pos))));
}
};
// ---------------------------------------------------------------------------
// Public API
// ---------------------------------------------------------------------------
string
encodeExpr(const Expr & e, const SymbolTable & symbols, const PosTable & positions, std::string_view filePath)
{
ASTEncoder enc(symbols, positions, filePath);
// The visitor API requires non-const Expr& and a unique_ptr&.
// We cast away const since encoding doesn't mutate the AST.
auto & mutableExpr = const_cast<Expr &>(e);
return enc.encode(mutableExpr);
}
} // namespace nix::wasm_codec
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