nix-super/src/libexpr/parser.y

%glr-parser
%define api.pure
%locations
%define parse.error verbose
%defines
/* %no-lines */
%parse-param { void * scanner }
%parse-param { nix::ParserState * state }
%lex-param { void * scanner }
%lex-param { nix::ParserState * state }
%expect 1
%expect-rr 1

%code requires {

#ifndef BISON_HEADER
#define BISON_HEADER

#include <variant>

#include "finally.hh"
#include "util.hh"
#include "users.hh"

#include "nixexpr.hh"
#include "eval.hh"
#include "eval-settings.hh"
#include "globals.hh"
#include "parser-state.hh"

#define YYLTYPE ::nix::ParserLocation
#define YY_DECL int yylex \
    (YYSTYPE * yylval_param, YYLTYPE * yylloc_param, yyscan_t yyscanner, nix::ParserState * state)

#endif

}

%{

#include "parser-tab.hh"
#include "lexer-tab.hh"

YY_DECL;

using namespace nix;

#define CUR_POS state->makeCurPos(*yylocp)


void yyerror(YYLTYPE * loc, yyscan_t scanner, ParserState * state, const char * error)
{
    throw ParseError({
        .msg = hintfmt(error),
        .errPos = state->state.positions[state->makeCurPos(*loc)]
    });
}


%}

%union {
  // !!! We're probably leaking stuff here.
  nix::Expr * e;
  nix::ExprList * list;
  nix::ExprAttrs * attrs;
  nix::Formals * formals;
  nix::Formal * formal;
  nix::NixInt n;
  nix::NixFloat nf;
  nix::StringToken id; // !!! -> Symbol
  nix::StringToken path;
  nix::StringToken uri;
  nix::StringToken str;
  std::vector<nix::AttrName> * attrNames;
  std::vector<std::pair<nix::PosIdx, nix::Expr *>> * string_parts;
  std::vector<std::pair<nix::PosIdx, std::variant<nix::Expr *, nix::StringToken>>> * ind_string_parts;
}

%type <e> start expr expr_function expr_if expr_op
%type <e> expr_select expr_simple expr_app
%type <list> expr_list
%type <attrs> binds
%type <formals> formals
%type <formal> formal
%type <attrNames> attrs attrpath
%type <string_parts> string_parts_interpolated
%type <ind_string_parts> ind_string_parts
%type <e> path_start string_parts string_attr
%type <id> attr
%token <id> ID
%token <str> STR IND_STR
%token <n> INT_LIT
%token <nf> FLOAT_LIT
%token <path> PATH HPATH SPATH PATH_END
%token <uri> URI
%token IF THEN ELSE ASSERT WITH LET IN_KW REC INHERIT EQ NEQ AND OR IMPL OR_KW
%token DOLLAR_CURLY /* == ${ */
%token IND_STRING_OPEN IND_STRING_CLOSE
%token ELLIPSIS

%right IMPL
%left OR
%left AND
%nonassoc EQ NEQ
%nonassoc '<' '>' LEQ GEQ
%right UPDATE
%left NOT
%left '+' '-'
%left '*' '/'
%right CONCAT
%nonassoc '?'
%nonassoc NEGATE

%%

start: expr { state->result = $1; };

expr: expr_function;

expr_function
  : ID ':' expr_function
    { $$ = new ExprLambda(CUR_POS, state->symbols.create($1), 0, $3); }
  | '{' formals '}' ':' expr_function
    { $$ = new ExprLambda(CUR_POS, state->validateFormals($2), $5); }
  | '{' formals '}' '@' ID ':' expr_function
    {
      auto arg = state->symbols.create($5);
      $$ = new ExprLambda(CUR_POS, arg, state->validateFormals($2, CUR_POS, arg), $7);
    }
  | ID '@' '{' formals '}' ':' expr_function
    {
      auto arg = state->symbols.create($1);
      $$ = new ExprLambda(CUR_POS, arg, state->validateFormals($4, CUR_POS, arg), $7);
    }
  | ASSERT expr ';' expr_function
    { $$ = new ExprAssert(CUR_POS, $2, $4); }
  | WITH expr ';' expr_function
    { $$ = new ExprWith(CUR_POS, $2, $4); }
  | LET binds IN_KW expr_function
    { if (!$2->dynamicAttrs.empty())
        throw ParseError({
            .msg = hintfmt("dynamic attributes not allowed in let"),
            .errPos = state->state.positions[CUR_POS]
        });
      $$ = new ExprLet($2, $4);
    }
  | expr_if
  ;

expr_if
  : IF expr THEN expr ELSE expr { $$ = new ExprIf(CUR_POS, $2, $4, $6); }
  | expr_op
  ;

expr_op
  : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
  | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->symbols.create("__sub")), {new ExprInt(0), $2}); }
  | expr_op EQ expr_op { $$ = new ExprOpEq($1, $3); }
  | expr_op NEQ expr_op { $$ = new ExprOpNEq($1, $3); }
  | expr_op '<' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3}); }
  | expr_op LEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1})); }
  | expr_op '>' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$3, $1}); }
  | expr_op GEQ expr_op { $$ = new ExprOpNot(new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__lessThan")), {$1, $3})); }
  | expr_op AND expr_op { $$ = new ExprOpAnd(state->makeCurPos(@2), $1, $3); }
  | expr_op OR expr_op { $$ = new ExprOpOr(state->makeCurPos(@2), $1, $3); }
  | expr_op IMPL expr_op { $$ = new ExprOpImpl(state->makeCurPos(@2), $1, $3); }
  | expr_op UPDATE expr_op { $$ = new ExprOpUpdate(state->makeCurPos(@2), $1, $3); }
  | expr_op '?' attrpath { $$ = new ExprOpHasAttr($1, std::move(*$3)); delete $3; }
  | expr_op '+' expr_op
    { $$ = new ExprConcatStrings(state->makeCurPos(@2), false, new std::vector<std::pair<PosIdx, Expr *> >({{state->makeCurPos(@1), $1}, {state->makeCurPos(@3), $3}})); }
  | expr_op '-' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__sub")), {$1, $3}); }
  | expr_op '*' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__mul")), {$1, $3}); }
  | expr_op '/' expr_op { $$ = new ExprCall(state->makeCurPos(@2), new ExprVar(state->symbols.create("__div")), {$1, $3}); }
  | expr_op CONCAT expr_op { $$ = new ExprOpConcatLists(state->makeCurPos(@2), $1, $3); }
  | expr_app
  ;

expr_app
  : expr_app expr_select {
      if (auto e2 = dynamic_cast<ExprCall *>($1)) {
          e2->args.push_back($2);
          $$ = $1;
      } else
          $$ = new ExprCall(CUR_POS, $1, {$2});
  }
  | expr_select
  ;

expr_select
  : expr_simple '.' attrpath
    { $$ = new ExprSelect(CUR_POS, $1, std::move(*$3), nullptr); delete $3; }
  | expr_simple '.' attrpath OR_KW expr_select
    { $$ = new ExprSelect(CUR_POS, $1, std::move(*$3), $5); delete $3; }
  | /* Backwards compatibility: because Nixpkgs has a rarely used
       function named ‘or’, allow stuff like ‘map or [...]’. */
    expr_simple OR_KW
    { $$ = new ExprCall(CUR_POS, $1, {new ExprVar(CUR_POS, state->symbols.create("or"))}); }
  | expr_simple
  ;

expr_simple
  : ID {
      std::string_view s = "__curPos";
      if ($1.l == s.size() && strncmp($1.p, s.data(), s.size()) == 0)
          $$ = new ExprPos(CUR_POS);
      else
          $$ = new ExprVar(CUR_POS, state->symbols.create($1));
  }
  | INT_LIT { $$ = new ExprInt($1); }
  | FLOAT_LIT { $$ = new ExprFloat($1); }
  | '"' string_parts '"' { $$ = $2; }
  | IND_STRING_OPEN ind_string_parts IND_STRING_CLOSE {
      $$ = state->stripIndentation(CUR_POS, std::move(*$2));
      delete $2;
  }
  | path_start PATH_END
  | path_start string_parts_interpolated PATH_END {
      $2->insert($2->begin(), {state->makeCurPos(@1), $1});
      $$ = new ExprConcatStrings(CUR_POS, false, $2);
  }
  | SPATH {
      std::string path($1.p + 1, $1.l - 2);
      $$ = new ExprCall(CUR_POS,
          new ExprVar(state->symbols.create("__findFile")),
          {new ExprVar(state->symbols.create("__nixPath")),
           new ExprString(std::move(path))});
  }
  | URI {
      static bool noURLLiterals = experimentalFeatureSettings.isEnabled(Xp::NoUrlLiterals);
      if (noURLLiterals)
          throw ParseError({
              .msg = hintfmt("URL literals are disabled"),
              .errPos = state->state.positions[CUR_POS]
          });
      $$ = new ExprString(std::string($1));
  }
  | '(' expr ')' { $$ = $2; }
  /* Let expressions `let {..., body = ...}' are just desugared
     into `(rec {..., body = ...}).body'. */
  | LET '{' binds '}'
    { $3->recursive = true; $$ = new ExprSelect(noPos, $3, state->symbols.create("body")); }
  | REC '{' binds '}'
    { $3->recursive = true; $$ = $3; }
  | '{' binds '}'
    { $$ = $2; }
  | '[' expr_list ']' { $$ = $2; }
  ;

string_parts
  : STR { $$ = new ExprString(std::string($1)); }
  | string_parts_interpolated { $$ = new ExprConcatStrings(CUR_POS, true, $1); }
  | { $$ = new ExprString(""); }
  ;

string_parts_interpolated
  : string_parts_interpolated STR
  { $$ = $1; $1->emplace_back(state->makeCurPos(@2), new ExprString(std::string($2))); }
  | string_parts_interpolated DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $3); }
  | DOLLAR_CURLY expr '}' { $$ = new std::vector<std::pair<PosIdx, Expr *>>; $$->emplace_back(state->makeCurPos(@1), $2); }
  | STR DOLLAR_CURLY expr '}' {
      $$ = new std::vector<std::pair<PosIdx, Expr *>>;
      $$->emplace_back(state->makeCurPos(@1), new ExprString(std::string($1)));
      $$->emplace_back(state->makeCurPos(@2), $3);
    }
  ;

path_start
  : PATH {
    Path path(absPath({$1.p, $1.l}, state->basePath.path.abs()));
    /* add back in the trailing '/' to the first segment */
    if ($1.p[$1.l-1] == '/' && $1.l > 1)
      path += "/";
    $$ = new ExprPath(ref<InputAccessor>(state->state.rootFS), std::move(path));
  }
  | HPATH {
    if (evalSettings.pureEval) {
        throw Error(
            "the path '%s' can not be resolved in pure mode",
            std::string_view($1.p, $1.l)
        );
    }
    Path path(getHome() + std::string($1.p + 1, $1.l - 1));
    $$ = new ExprPath(ref<InputAccessor>(state->state.rootFS), std::move(path));
  }
  ;

ind_string_parts
  : ind_string_parts IND_STR { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $2); }
  | ind_string_parts DOLLAR_CURLY expr '}' { $$ = $1; $1->emplace_back(state->makeCurPos(@2), $3); }
  | { $$ = new std::vector<std::pair<PosIdx, std::variant<Expr *, StringToken>>>; }
  ;

binds
  : binds attrpath '=' expr ';' { $$ = $1; state->addAttr($$, std::move(*$2), $4, state->makeCurPos(@2)); delete $2; }
  | binds INHERIT attrs ';'
    { $$ = $1;
      for (auto & i : *$3) {
          if ($$->attrs.find(i.symbol) != $$->attrs.end())
              state->dupAttr(i.symbol, state->makeCurPos(@3), $$->attrs[i.symbol].pos);
          auto pos = state->makeCurPos(@3);
          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprVar(CUR_POS, i.symbol), pos, true));
      }
      delete $3;
    }
  | binds INHERIT '(' expr ')' attrs ';'
    { $$ = $1;
      /* !!! Should ensure sharing of the expression in $4. */
      for (auto & i : *$6) {
          if ($$->attrs.find(i.symbol) != $$->attrs.end())
              state->dupAttr(i.symbol, state->makeCurPos(@6), $$->attrs[i.symbol].pos);
          $$->attrs.emplace(i.symbol, ExprAttrs::AttrDef(new ExprSelect(CUR_POS, $4, i.symbol), state->makeCurPos(@6)));
      }
      delete $6;
    }
  | { $$ = new ExprAttrs(state->makeCurPos(@0)); }
  ;

attrs
  : attrs attr { $$ = $1; $1->push_back(AttrName(state->symbols.create($2))); }
  | attrs string_attr
    { $$ = $1;
      ExprString * str = dynamic_cast<ExprString *>($2);
      if (str) {
          $$->push_back(AttrName(state->symbols.create(str->s)));
          delete str;
      } else
          throw ParseError({
              .msg = hintfmt("dynamic attributes not allowed in inherit"),
              .errPos = state->state.positions[state->makeCurPos(@2)]
          });
    }
  | { $$ = new AttrPath; }
  ;

attrpath
  : attrpath '.' attr { $$ = $1; $1->push_back(AttrName(state->symbols.create($3))); }
  | attrpath '.' string_attr
    { $$ = $1;
      ExprString * str = dynamic_cast<ExprString *>($3);
      if (str) {
          $$->push_back(AttrName(state->symbols.create(str->s)));
          delete str;
      } else
          $$->push_back(AttrName($3));
    }
  | attr { $$ = new std::vector<AttrName>; $$->push_back(AttrName(state->symbols.create($1))); }
  | string_attr
    { $$ = new std::vector<AttrName>;
      ExprString *str = dynamic_cast<ExprString *>($1);
      if (str) {
          $$->push_back(AttrName(state->symbols.create(str->s)));
          delete str;
      } else
          $$->push_back(AttrName($1));
    }
  ;

attr
  : ID
  | OR_KW { $$ = {"or", 2}; }
  ;

string_attr
  : '"' string_parts '"' { $$ = $2; }
  | DOLLAR_CURLY expr '}' { $$ = $2; }
  ;

expr_list
  : expr_list expr_select { $$ = $1; $1->elems.push_back($2); /* !!! dangerous */ }
  | { $$ = new ExprList; }
  ;

formals
  : formal ',' formals
    { $$ = $3; $$->formals.emplace_back(*$1); delete $1; }
  | formal
    { $$ = new Formals; $$->formals.emplace_back(*$1); $$->ellipsis = false; delete $1; }
  |
    { $$ = new Formals; $$->ellipsis = false; }
  | ELLIPSIS
    { $$ = new Formals; $$->ellipsis = true; }
  ;

formal
  : ID { $$ = new Formal{CUR_POS, state->symbols.create($1), 0}; }
  | ID '?' expr { $$ = new Formal{CUR_POS, state->symbols.create($1), $3}; }
  ;

%%


#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "eval.hh"
#include "filetransfer.hh"
#include "tarball.hh"
#include "store-api.hh"
#include "flake/flake.hh"
#include "fs-input-accessor.hh"
#include "memory-input-accessor.hh"


namespace nix {

unsigned long Expr::nrExprs = 0;

Expr * EvalState::parse(
    char * text,
    size_t length,
    Pos::Origin origin,
    const SourcePath & basePath,
    std::shared_ptr<StaticEnv> & staticEnv)
{
    yyscan_t scanner;
    ParserState state {
        .state = *this,
        .symbols = symbols,
        .basePath = basePath,
        .origin = {origin},
    };

    yylex_init(&scanner);
    Finally _destroy([&] { yylex_destroy(scanner); });

    yy_scan_buffer(text, length, scanner);
    yyparse(scanner, &state);

    state.result->bindVars(*this, staticEnv);

    return state.result;
}


SourcePath resolveExprPath(SourcePath path)
{
    unsigned int followCount = 0, maxFollow = 1024;

    /* If `path' is a symlink, follow it.  This is so that relative
       path references work. */
    while (!path.path.isRoot()) {
        // Basic cycle/depth limit to avoid infinite loops.
        if (++followCount >= maxFollow)
            throw Error("too many symbolic links encountered while traversing the path '%s'", path);
        auto p = path.parent().resolveSymlinks() + path.baseName();
        if (p.lstat().type != InputAccessor::tSymlink) break;
        path = {path.accessor, CanonPath(p.readLink(), path.path.parent().value_or(CanonPath::root))};
    }

    /* If `path' refers to a directory, append `/default.nix'. */
    if (path.resolveSymlinks().lstat().type == InputAccessor::tDirectory)
        return path + "default.nix";

    return path;
}


Expr * EvalState::parseExprFromFile(const SourcePath & path)
{
    return parseExprFromFile(path, staticBaseEnv);
}


Expr * EvalState::parseExprFromFile(const SourcePath & path, std::shared_ptr<StaticEnv> & staticEnv)
{
    auto buffer = path.resolveSymlinks().readFile();
    // readFile hopefully have left some extra space for terminators
    buffer.append("\0\0", 2);
    return parse(buffer.data(), buffer.size(), Pos::Origin(path), path.parent(), staticEnv);
}


Expr * EvalState::parseExprFromString(std::string s_, const SourcePath & basePath, std::shared_ptr<StaticEnv> & staticEnv)
{
    auto s = make_ref<std::string>(std::move(s_));
    s->append("\0\0", 2);
    return parse(s->data(), s->size(), Pos::String{.source = s}, basePath, staticEnv);
}


Expr * EvalState::parseExprFromString(std::string s, const SourcePath & basePath)
{
    return parseExprFromString(std::move(s), basePath, staticBaseEnv);
}


Expr * EvalState::parseStdin()
{
    //Activity act(*logger, lvlTalkative, "parsing standard input");
    auto buffer = drainFD(0);
    // drainFD should have left some extra space for terminators
    buffer.append("\0\0", 2);
    auto s = make_ref<std::string>(std::move(buffer));
    return parse(s->data(), s->size(), Pos::Stdin{.source = s}, rootPath(CanonPath::fromCwd()), staticBaseEnv);
}


SourcePath EvalState::findFile(const std::string_view path)
{
    return findFile(searchPath, path);
}


SourcePath EvalState::findFile(const SearchPath & searchPath, const std::string_view path, const PosIdx pos)
{
    for (auto & i : searchPath.elements) {
        auto suffixOpt = i.prefix.suffixIfPotentialMatch(path);

        if (!suffixOpt) continue;
        auto suffix = *suffixOpt;

        auto rOpt = resolveSearchPathPath(i.path);
        if (!rOpt) continue;
        auto r = *rOpt;

        Path res = suffix == "" ? r : concatStrings(r, "/", suffix);
        if (pathExists(res)) return rootPath(CanonPath(canonPath(res)));
    }

    if (hasPrefix(path, "nix/"))
        return {corepkgsFS, CanonPath(path.substr(3))};

    debugThrow(ThrownError({
        .msg = hintfmt(evalSettings.pureEval
            ? "cannot look up '<%s>' in pure evaluation mode (use '--impure' to override)"
            : "file '%s' was not found in the Nix search path (add it using $NIX_PATH or -I)",
            path),
        .errPos = positions[pos]
    }), 0, 0);
}


std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Path & value0, bool initAccessControl)
{
    auto & value = value0.s;
    auto i = searchPathResolved.find(value);
    if (i != searchPathResolved.end()) return i->second;

    std::optional<std::string> res;

    if (EvalSettings::isPseudoUrl(value)) {
        try {
            auto storePath = fetchers::downloadTarball(
                store, EvalSettings::resolvePseudoUrl(value), "source", false).storePath;
            res = { store->toRealPath(storePath) };
        } catch (FileTransferError & e) {
            logWarning({
                .msg = hintfmt("Nix search path entry '%1%' cannot be downloaded, ignoring", value)
            });
        }
    }

    else if (hasPrefix(value, "flake:")) {
        experimentalFeatureSettings.require(Xp::Flakes);
        auto flakeRef = parseFlakeRef(value.substr(6), {}, true, false);
        debug("fetching flake search path element '%s''", value);
        auto storePath = flakeRef.resolve(store).fetchTree(store).first;
        res = { store->toRealPath(storePath) };
    }

    else {
        auto path = absPath(value);

        /* Allow access to paths in the search path. */
        if (initAccessControl) {
            allowPath(path);
            if (store->isInStore(path)) {
                try {
                    StorePathSet closure;
                    store->computeFSClosure(store->toStorePath(path).first, closure);
                    for (auto & p : closure)
                        allowPath(p);
                } catch (InvalidPath &) { }
            }
        }

        if (pathExists(path))
            res = { path };
        else {
            logWarning({
                .msg = hintfmt("Nix search path entry '%1%' does not exist, ignoring", value)
            });
            res = std::nullopt;
        }
    }

    if (res)
        debug("resolved search path element '%s' to '%s'", value, *res);
    else
        debug("failed to resolve search path element '%s'", value);

    searchPathResolved.emplace(value, res);
    return res;
}


}