desugarer.cpp

/*
Copyright 2015 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

#include <cassert>

#include <algorithm>

#include "ast.h"
#include "desugarer.h"
#include "lexer.h"
#include "parser.h"
#include "pass.h"
#include "string_utils.h"

static const Fodder EF;  // Empty fodder.

static const LocationRange E;  // Empty.

struct BuiltinDecl {
    UString name;
    std::vector<UString> params;
};

static unsigned long max_builtin = 37;
BuiltinDecl jsonnet_builtin_decl(unsigned long builtin)
{
    switch (builtin) {
        case 0: return {U"makeArray", {U"sz", U"func"}};
        case 1: return {U"pow", {U"x", U"n"}};
        case 2: return {U"floor", {U"x"}};
        case 3: return {U"ceil", {U"x"}};
        case 4: return {U"sqrt", {U"x"}};
        case 5: return {U"sin", {U"x"}};
        case 6: return {U"cos", {U"x"}};
        case 7: return {U"tan", {U"x"}};
        case 8: return {U"asin", {U"x"}};
        case 9: return {U"acos", {U"x"}};
        case 10: return {U"atan", {U"x"}};
        case 11: return {U"type", {U"x"}};
        case 12: return {U"filter", {U"func", U"arr"}};
        case 13: return {U"objectHasEx", {U"obj", U"f", U"inc_hidden"}};
        case 14: return {U"length", {U"x"}};
        case 15: return {U"objectFieldsEx", {U"obj", U"inc_hidden"}};
        case 16: return {U"codepoint", {U"str"}};
        case 17: return {U"char", {U"n"}};
        case 18: return {U"log", {U"n"}};
        case 19: return {U"exp", {U"n"}};
        case 20: return {U"mantissa", {U"n"}};
        case 21: return {U"exponent", {U"n"}};
        case 22: return {U"modulo", {U"a", U"b"}};
        case 23: return {U"extVar", {U"x"}};
        case 24: return {U"primitiveEquals", {U"a", U"b"}};
        case 25: return {U"native", {U"name"}};
        case 26: return {U"md5", {U"str"}};
        case 27: return {U"trace", {U"str", U"rest"}};
        case 28: return {U"splitLimit", {U"str", U"c", U"maxsplits"}};
        case 29: return {U"substr", {U"str", U"from", U"len"}};
        case 30: return {U"range", {U"from", U"to"}};
        case 31: return {U"strReplace", {U"str", U"from", U"to"}};
        case 32: return {U"asciiLower", {U"str"}};
        case 33: return {U"asciiUpper", {U"str"}};
        case 34: return {U"join", {U"sep", U"arr"}};
        case 35: return {U"parseJson", {U"str"}};
        case 36: return {U"encodeUTF8", {U"str"}};
        case 37: return {U"decodeUTF8", {U"arr"}};
        default:
            std::cerr << "INTERNAL ERROR: Unrecognized builtin function: " << builtin << std::endl;
            std::abort();
    }
    // Quiet, compiler.
    return BuiltinDecl();
}

static constexpr char STD_CODE[] = {
#include "std.jsonnet.h"
};

/** Desugar Jsonnet expressions to reduce the number of constructs the rest of the implementation
 * needs to understand.
 *
 * Desugaring should happen immediately after parsing, i.e. before static analysis and execution.
 * Temporary variables introduced here should be prefixed with $ to ensure they do not clash with
 * variables used in user code.
 */
class Desugarer {
    Allocator *alloc;

    template <class T, class... Args>
    T *make(Args &&... args)
    {
        return alloc->make<T>(std::forward<Args>(args)...);
    }

    AST *clone(AST *ast)
    {
        return clone_ast(*alloc, ast);
    }

    const Identifier *id(const UString &s)
    {
        return alloc->makeIdentifier(s);
    }

    LiteralString *str(const UString &s)
    {
        return make<LiteralString>(E, EF, s, LiteralString::DOUBLE, "", "");
    }

    LiteralString *str(const LocationRange &loc, const UString &s)
    {
        return make<LiteralString>(loc, EF, s, LiteralString::DOUBLE, "", "");
    }

    LiteralNull *null(void)
    {
        return make<LiteralNull>(E, EF);
    }

    Var *var(const Identifier *ident)
    {
        return make<Var>(E, EF, ident);
    }

    Var *std(void)
    {
        return var(id(U"std"));
    }

    Local::Bind bind(const Identifier *id, AST *body)
    {
        return Local::Bind(EF, id, EF, body, false, EF, ArgParams{}, false, EF, EF);
    }

    Local::Binds singleBind(const Identifier *id, AST *body)
    {
        return {bind(id, body)};
    }

    Array *singleton(AST *body)
    {
        return make<Array>(
            body->location, EF, Array::Elements{Array::Element(body, EF)}, false, EF);
    }

    Apply *stdFunc(const UString &name, AST *v)
    {
        return make<Apply>(
            v->location,
            EF,
            make<Index>(E, EF, std(), EF, false, str(name), EF, nullptr, EF, nullptr, EF),
            EF,
            ArgParams{{v, EF}},
            false,  // trailingComma
            EF,
            EF,
            true  // tailstrict
        );
    }

    Apply *stdFunc(const LocationRange &loc, const UString &name, AST *a, AST *b)
    {
        return make<Apply>(
            loc,
            EF,
            make<Index>(E, EF, std(), EF, false, str(name), EF, nullptr, EF, nullptr, EF),
            EF,
            ArgParams{{a, EF}, {b, EF}},
            false,  // trailingComma
            EF,
            EF,
            true  // tailstrict
        );
    }

    Apply *length(AST *v)
    {
        return stdFunc(U"length", v);
    }

    Apply *type(AST *v)
    {
        return stdFunc(U"type", v);
    }

    Apply *primitiveEquals(const LocationRange &loc, AST *a, AST *b)
    {
        return stdFunc(loc, U"primitiveEquals", a, b);
    }

    Apply *equals(const LocationRange &loc, AST *a, AST *b)
    {
        return stdFunc(loc, U"equals", a, b);
    }

    Error *error(AST *msg)
    {
        return make<Error>(msg->location, EF, msg);
    }

    Error *error(const LocationRange &loc, const UString &msg)
    {
        return error(str(loc, msg));
    }

   public:
    Desugarer(Allocator *alloc) : alloc(alloc) {}

    void desugarParams(ArgParams &params, unsigned obj_level)
    {
        for (auto &param : params) {
            if (param.expr) {
                // Default arg.
                desugar(param.expr, obj_level);
            }
        }
    }

    // For all occurrences, records the identifier that will replace super[e]
    // If self occurs, also map the self identifier to nullptr.
    typedef std::vector<std::pair<const Identifier *, AST *>> SuperVars;

    SuperVars desugarFields(AST *ast, ObjectFields &fields, unsigned obj_level)
    {
        // Desugar children
        for (auto &field : fields) {
            if (field.expr1 != nullptr)
                desugar(field.expr1, obj_level);
            desugar(field.expr2, obj_level + 1);
            if (field.expr3 != nullptr)
                desugar(field.expr3, obj_level + 1);
            desugarParams(field.params, obj_level + 1);
        }

        // Simplify asserts
        for (auto &field : fields) {
            if (field.kind != ObjectField::ASSERT)
                continue;
            AST *msg = field.expr3;
            field.expr3 = nullptr;
            if (msg == nullptr) {
                // The location is what appears in the stacktrace.
                msg = str(field.expr2->location, U"Object assertion failed.");
            }

            // if expr2 then true else error msg
            field.expr2 = make<Conditional>(field.expr2->location,
                                            EF,
                                            field.expr2,
                                            EF,
                                            make<LiteralBoolean>(E, EF, true),
                                            EF,
                                            error(msg));
        }

        // Remove methods
        for (auto &field : fields) {
            if (!field.methodSugar)
                continue;
            field.expr2 = make<Function>(field.expr2->location,
                                         EF,
                                         field.fodderL,
                                         field.params,
                                         field.trailingComma,
                                         field.fodderR,
                                         field.expr2);
            field.methodSugar = false;
            field.params.clear();
        }

        // Remove object-level locals
        auto copy = fields;
        fields.clear();
        Local::Binds binds;
        for (auto &local : copy) {
            if (local.kind != ObjectField::LOCAL)
                continue;
            binds.push_back(bind(local.id, local.expr2));
        }
        for (auto &field : copy) {
            if (field.kind == ObjectField::LOCAL)
                continue;
            if (!binds.empty())
                field.expr2 = make<Local>(field.expr2->location, EF, binds, field.expr2);
            fields.push_back(field);
        }

        // Change all to FIELD_EXPR
        for (auto &field : fields) {
            switch (field.kind) {
                case ObjectField::ASSERT:
                    // Nothing to do.
                    break;

                case ObjectField::FIELD_ID:
                    field.expr1 = str(field.id->name);
                    field.kind = ObjectField::FIELD_EXPR;
                    break;

                case ObjectField::FIELD_EXPR:
                    // Nothing to do.
                    break;

                case ObjectField::FIELD_STR:
                    // Just set the flag.
                    field.kind = ObjectField::FIELD_EXPR;
                    break;

                case ObjectField::LOCAL:
                    std::cerr << "Locals should be removed by now." << std::endl;
                    abort();
            }
        }

        /** Replaces all occurrences of self, super[f] and e in super with variables.
         *
         * Returns all variables and original expressions via super_vars.
         */
        class SubstituteSelfSuper : public CompilerPass {
            Desugarer *desugarer;
            SuperVars &superVars;
            unsigned &counter;
            const Identifier *newSelf;

           public:
            SubstituteSelfSuper(Desugarer *desugarer, SuperVars &super_vars, unsigned &counter)
                : CompilerPass(*desugarer->alloc),
                  desugarer(desugarer),
                  superVars(super_vars),
                  counter(counter),
                  newSelf(nullptr)
            {
            }
            void visitExpr(AST *&expr)
            {
                if (dynamic_cast<Self *>(expr)) {
                    if (newSelf == nullptr) {
                        newSelf = desugarer->id(U"$outer_self");
                        superVars.emplace_back(newSelf, nullptr);
                    }
                    expr = alloc.make<Var>(expr->location, expr->openFodder, newSelf);
                } else if (auto *super_index = dynamic_cast<SuperIndex *>(expr)) {
                    UStringStream ss;
                    ss << U"$outer_super_index" << (counter++);
                    const Identifier *super_var = desugarer->id(ss.str());
                    // Desugaring of expr should already have occurred.
                    assert(super_index->index != nullptr);
                    // Re-use super_index since we're replacing it here.
                    superVars.emplace_back(super_var, super_index);
                    expr = alloc.make<Var>(expr->location, expr->openFodder, super_var);
                } else if (auto *in_super = dynamic_cast<InSuper *>(expr)) {
                    UStringStream ss;
                    ss << U"$outer_in_super" << (counter++);
                    const Identifier *in_super_var = desugarer->id(ss.str());
                    // Re-use in_super since we're replacing it here.
                    superVars.emplace_back(in_super_var, in_super);
                    expr = alloc.make<Var>(expr->location, expr->openFodder, in_super_var);
                }
                CompilerPass::visitExpr(expr);
            }
        };

        SuperVars super_vars;
        unsigned counter = 0;

        // Remove +:
        for (auto &field : fields) {
            if (!field.superSugar)
                continue;
            // We have to bind self/super from expr1 outside the class, as we copy the expression
            // into the field body.
            // Clone it so that we maintain the AST as a tree.
            AST *index = clone(field.expr1);
            // This will remove self/super.
            SubstituteSelfSuper(this, super_vars, counter).expr(index);
            field.expr2 = make<Conditional>(
                ast->location,
                EF,
                make<InSuper>(ast->location, EF, index, EF, EF),
                EF,
                make<Binary>(ast->location,
                             EF,
                             make<SuperIndex>(ast->location, EF, EF, clone(index), EF, nullptr),
                             EF,
                             BOP_PLUS,
                             field.expr2),
                EF,
                clone(field.expr2));
            field.superSugar = false;
        }

        return super_vars;
    }

    AST* makeArrayComprehension(ArrayComprehension *ast) {
        int n = ast->specs.size();
        AST *zero = make<LiteralNumber>(E, EF, "0.0");
        AST *one = make<LiteralNumber>(E, EF, "1.0");
        auto *_r = id(U"$r");
        auto *_l = id(U"$l");
        std::vector<const Identifier *> _i(n);
        for (int i = 0; i < n; ++i) {
            UStringStream ss;
            ss << U"$i_" << i;
            _i[i] = id(ss.str());
        }
        std::vector<const Identifier *> _aux(n);
        for (int i = 0; i < n; ++i) {
            UStringStream ss;
            ss << U"$aux_" << i;
            _aux[i] = id(ss.str());
        }

        // Build it from the inside out.  We keep wrapping 'in' with more ASTs.
        assert(ast->specs[0].kind == ComprehensionSpec::FOR);

        int last_for = n - 1;
        while (ast->specs[last_for].kind != ComprehensionSpec::FOR)
            last_for--;
        // $aux_{last_for}($i_{last_for} + 1, $r + [body])
        AST *in = make<Apply>(
            ast->body->location,
            EF,
            var(_aux[last_for]),
            EF,
            ArgParams{{make<Binary>(E, EF, var(_i[last_for]), EF, BOP_PLUS, one), EF},
                {make<Binary>(E, EF, var(_r), EF, BOP_PLUS, singleton(ast->body)), EF}},
            false,  // trailingComma
            EF,
            EF,
            true  // tailstrict
        );
        for (int i = n - 1; i >= 0; --i) {
            const ComprehensionSpec &spec = ast->specs[i];
            AST *out;
            if (i > 0) {
                int prev_for = i - 1;
                while (ast->specs[prev_for].kind != ComprehensionSpec::FOR)
                    prev_for--;

                // aux_{prev_for}($i_{prev_for} + 1, $r)
                out = make<Apply>(  // False branch.
                    E,
                    EF,
                    var(_aux[prev_for]),
                    EF,
                    ArgParams{{
                        make<Binary>(E, EF, var(_i[prev_for]), EF, BOP_PLUS, one),
                            EF,
                            },
                      {
                        var(_r),
                            EF,
                            }},
                    false,  // trailingComma
                    EF,
                    EF,
                    true  // tailstrict
                );
            } else {
                out = var(_r);
            }
            switch (spec.kind) {
                case ComprehensionSpec::IF: {
                  /*
                    if [[[...cond...]]] then
                    [[[...in...]]]
                    else
                    [[[...out...]]]
                  */
                    in = make<Conditional>(ast->location,
                                           EF,
                                           spec.expr,
                                           EF,
                                           in,  // True branch.
                                           EF,
                                           out);  // False branch.
                } break;
                case ComprehensionSpec::FOR: {
                    /*
                      local $l = [[[...array...]]]
                      aux_{i}(i_{i}, r) =
                      if i_{i} >= std.length($l) then
                      [[[...out...]]]
                      else
                      local [[[...var...]]] = $l[i_{i}];
                      [[[...in...]]];
                      if std.type($l) == "array" then
                      aux_{i}(0, $r) tailstrict
                      else
                      error "In comprehension, can only iterate over array..";
                    */
                    in = make<Local>(
                        ast->location,
                        EF,
                        Local::Binds{
                          bind(_l, spec.expr),  // Need to check expr is an array
                              bind(_aux[i],
                                   make<Function>(
                                       ast->location,
                                       EF,
                                       EF,
                                       ArgParams{{EF, _i[i], EF}, {EF, _r, EF}},
                                       false,  // trailingComma
                                       EF,
                                       make<Conditional>(ast->location,
                                                         EF,
                                                         make<Binary>(E,
                                                                      EF,
                                                                      var(_i[i]),
                                                                      EF,
                                                                      BOP_GREATER_EQ,
                                                                      length(var(_l))),
                                                         EF,
                                                         out,
                                                         EF,
                                                         make<Local>(
                                                             ast->location,
                                                             EF,
                                                             singleBind(spec.var,
                                                                        make<Index>(E,
                                                                                    EF,
                                                                                    var(_l),
                                                                                    EF,
                                                                                    false,
                                                                                    var(_i[i]),
                                                                                    EF,
                                                                                    nullptr,
                                                                                    EF,
                                                                                    nullptr,
                                                                                    EF)),
                                                             in))))},
                        make<Conditional>(
                            ast->location,
                            EF,
                            equals(ast->location, type(var(_l)), str(U"array")),
                            EF,
                            make<Apply>(
                                E,
                                EF,
                                var(_aux[i]),
                                EF,
                                ArgParams{{zero, EF},
                                  {
                                    i == 0 ? make<Array>(
                                        E, EF, Array::Elements{}, false, EF)
                                        : static_cast<AST *>(var(_r)),
                                        EF,
                                        }},
                                false,  // trailingComma
                                EF,
                                EF,
                                true),  // tailstrict
                            EF,
                            error(ast->location,
                                  U"In comprehension, can only iterate over array.")));
                } break;
            }
        }

        return in;
    }

    AST* makeObject(Object *ast, unsigned obj_level) {
        // Hidden variable to allow outer/top binding.
        if (obj_level == 0) {
            const Identifier *hidden_var = id(U"$");
            auto *body = make<Self>(E, EF);
            ast->fields.push_back(ObjectField::Local(EF, EF, hidden_var, EF, body, EF));
        }

        SuperVars svs = desugarFields(ast, ast->fields, obj_level);

        DesugaredObject::Fields new_fields;
        ASTs new_asserts;
        for (const ObjectField &field : ast->fields) {
            if (field.kind == ObjectField::ASSERT) {
                new_asserts.push_back(field.expr2);
            } else if (field.kind == ObjectField::FIELD_EXPR) {
                new_fields.emplace_back(field.hide, field.expr1, field.expr2);
            } else {
                std::cerr << "INTERNAL ERROR: field should have been desugared: " << field.kind
                          << std::endl;
            }
        }

        AST* retval = make<DesugaredObject>(ast->location, new_asserts, new_fields);
        if (svs.size() > 0) {
            Local::Binds binds;
            for (const auto &pair : svs) {
                if (pair.second == nullptr) {
                    // Self binding
                    binds.push_back(bind(pair.first, make<Self>(E, EF)));
                } else {
                    // Super binding
                    binds.push_back(bind(pair.first, pair.second));
                }
            }
            retval = make<Local>(ast->location, EF, binds, retval);
        }

        return retval;
    }

    AST* makeObjectComprehension(ObjectComprehension *ast, unsigned obj_level) {
        // Hidden variable to allow outer/top binding.
        if (obj_level == 0) {
            const Identifier *hidden_var = id(U"$");
            auto *body = make<Self>(E, EF);
            ast->fields.push_back(ObjectField::Local(EF, EF, hidden_var, EF, body, EF));
        }

        SuperVars svs = desugarFields(ast, ast->fields, obj_level);

        for (ComprehensionSpec &spec : ast->specs)
            desugar(spec.expr, obj_level);

        AST *field = ast->fields.front().expr1;
        AST *value = ast->fields.front().expr2;

        /*  {
            [arr[0]]: local x = arr[1], y = arr[2], z = arr[3]; val_expr
            for arr in [ [key_expr, x, y, z] for ...  ]
            }
        */
        auto *_arr = id(U"$arr");
        AST *zero = make<LiteralNumber>(E, EF, "0.0");
        int counter = 1;
        Local::Binds binds;
        Array::Elements arr_e{Array::Element(field, EF)};
        for (ComprehensionSpec &spec : ast->specs) {
            if (spec.kind == ComprehensionSpec::FOR) {
                std::stringstream num;
                num << counter++;
                binds.push_back(bind(spec.var,
                                     make<Index>(E,
                                                 EF,
                                                 var(_arr),
                                                 EF,
                                                 false,
                                                 make<LiteralNumber>(E, EF, num.str()),
                                                 EF,
                                                 nullptr,
                                                 EF,
                                                 nullptr,
                                                 EF)));
                arr_e.emplace_back(var(spec.var), EF);
            }
        }
        AST *arr = make<ArrayComprehension>(ast->location,
                                            EF,
                                            make<Array>(ast->location, EF, arr_e, false, EF),
                                            EF,
                                            false,
                                            ast->specs,
                                            EF);
        desugar(arr, obj_level);
        return make<ObjectComprehensionSimple>(
            ast->location,
            make<Index>(E, EF, var(_arr), EF, false, zero, EF, nullptr, EF, nullptr, EF),
            make<Local>(ast->location, EF, binds, value),
            _arr,
            arr);
    }

    void desugar(AST *&ast_, unsigned obj_level)
    {
        if (auto *ast = dynamic_cast<Apply *>(ast_)) {
            desugar(ast->target, obj_level);
            for (ArgParam &arg : ast->args)
                desugar(arg.expr, obj_level);

        } else if (auto *ast = dynamic_cast<ApplyBrace *>(ast_)) {
            desugar(ast->left, obj_level);
            desugar(ast->right, obj_level);
            ast_ =
                make<Binary>(ast->location, ast->openFodder, ast->left, EF, BOP_PLUS, ast->right);

        } else if (auto *ast = dynamic_cast<Array *>(ast_)) {
            for (auto &el : ast->elements)
                desugar(el.expr, obj_level);

        } else if (auto *ast = dynamic_cast<ArrayComprehension *>(ast_)) {
            for (ComprehensionSpec &spec : ast->specs)
                desugar(spec.expr, obj_level);
            desugar(ast->body, obj_level + 1);

            ast_ = makeArrayComprehension(ast);

        } else if (auto *ast = dynamic_cast<Assert *>(ast_)) {
            desugar(ast->cond, obj_level);
            if (ast->message == nullptr) {
                ast->message = str(U"Assertion failed.");
            }
            desugar(ast->message, obj_level);
            desugar(ast->rest, obj_level);

            // if cond then rest else error msg
            AST *branch_false = make<Error>(ast->location, EF, ast->message);
            ast_ = make<Conditional>(
                ast->location, ast->openFodder, ast->cond, EF, ast->rest, EF, branch_false);

        } else if (auto *ast = dynamic_cast<Binary *>(ast_)) {
            desugar(ast->left, obj_level);
            desugar(ast->right, obj_level);

            bool invert = false;

            switch (ast->op) {
                case BOP_PERCENT: {
                    AST *f_mod = make<Index>(
                        E, EF, std(), EF, false, str(U"mod"), EF, nullptr, EF, nullptr, EF);
                    ArgParams args = {{ast->left, EF}, {ast->right, EF}};
                    ast_ = make<Apply>(
                        ast->location, ast->openFodder, f_mod, EF, args, false, EF, EF, false);
                } break;

                case BOP_MANIFEST_UNEQUAL: invert = true;
                case BOP_MANIFEST_EQUAL: {
                    ast_ = equals(ast->location, ast->left, ast->right);
                    if (invert)
                        ast_ = make<Unary>(ast->location, ast->openFodder, UOP_NOT, ast_);
                } break;

                default:;
                    // Otherwise don't change it.
            }

        } else if (dynamic_cast<const BuiltinFunction *>(ast_)) {
            // Nothing to do.

        } else if (auto *ast = dynamic_cast<Conditional *>(ast_)) {
            desugar(ast->cond, obj_level);
            desugar(ast->branchTrue, obj_level);
            if (ast->branchFalse == nullptr)
                ast->branchFalse = null();
            desugar(ast->branchFalse, obj_level);

        } else if (auto *ast = dynamic_cast<Dollar *>(ast_)) {
            if (obj_level == 0) {
                throw StaticError(ast->location, "No top-level object found.");
            }
            ast_ = var(id(U"$"));

        } else if (auto *ast = dynamic_cast<Error *>(ast_)) {
            desugar(ast->expr, obj_level);

        } else if (auto *ast = dynamic_cast<Function *>(ast_)) {
            desugar(ast->body, obj_level);
            desugarParams(ast->params, obj_level);

        } else if (auto *ast = dynamic_cast<Import *>(ast_)) {
            // TODO(dcunnin): Abstract this into a template function if it becomes more common.
            AST *file = ast->file;
            desugar(file, obj_level);
            ast->file = dynamic_cast<LiteralString *>(file);

        } else if (auto *ast = dynamic_cast<Importstr *>(ast_)) {
            // TODO(dcunnin): Abstract this into a template function if it becomes more common.
            AST *file = ast->file;
            desugar(file, obj_level);
            ast->file = dynamic_cast<LiteralString *>(file);

        } else if (auto *ast = dynamic_cast<InSuper *>(ast_)) {
            desugar(ast->element, obj_level);

        } else if (auto *ast = dynamic_cast<Index *>(ast_)) {
            desugar(ast->target, obj_level);
            if (ast->isSlice) {
                if (ast->index == nullptr)
                    ast->index = null();
                desugar(ast->index, obj_level);

                if (ast->end == nullptr)
                    ast->end = null();
                desugar(ast->end, obj_level);

                if (ast->step == nullptr)
                    ast->step = null();
                desugar(ast->step, obj_level);

                ast_ = make<Apply>(
                    ast->location,
                    EF,
                    make<Index>(
                        E, EF, std(), EF, false, str(U"slice"), EF, nullptr, EF, nullptr, EF),
                    EF,
                    ArgParams{
                        {ast->target, EF},
                        {ast->index, EF},
                        {ast->end, EF},
                        {ast->step, EF},
                    },
                    false,  // trailing comma
                    EF,
                    EF,
                    false  // tailstrict
                );
            } else {
                if (ast->id != nullptr) {
                    assert(ast->index == nullptr);
                    ast->index = str(ast->id->name);
                    ast->id = nullptr;
                }
                desugar(ast->index, obj_level);
            }

        } else if (auto *ast = dynamic_cast<Local *>(ast_)) {
            for (auto &bind : ast->binds)
                desugar(bind.body, obj_level);
            desugar(ast->body, obj_level);

            for (auto &bind : ast->binds) {
                if (bind.functionSugar) {
                    desugarParams(bind.params, obj_level);
                    bind.body = make<Function>(ast->location,
                                               ast->openFodder,
                                               bind.parenLeftFodder,
                                               bind.params,
                                               false,
                                               bind.parenRightFodder,
                                               bind.body);
                    bind.functionSugar = false;
                    bind.params.clear();
                }
            }

        } else if (dynamic_cast<const LiteralBoolean *>(ast_)) {
            // Nothing to do.

        } else if (dynamic_cast<const LiteralNumber *>(ast_)) {
            // Nothing to do.

        } else if (auto *ast = dynamic_cast<LiteralString *>(ast_)) {
            if ((ast->tokenKind != LiteralString::BLOCK) &&
                (ast->tokenKind != LiteralString::VERBATIM_DOUBLE) &&
                (ast->tokenKind != LiteralString::VERBATIM_SINGLE)) {
                ast->value = jsonnet_string_unescape(ast->location, ast->value);
            }
            ast->tokenKind = LiteralString::DOUBLE;
            ast->blockIndent.clear();

        } else if (dynamic_cast<const LiteralNull *>(ast_)) {
            // Nothing to do.

        } else if (auto *ast = dynamic_cast<DesugaredObject *>(ast_)) {
            for (auto &field : ast->fields) {
                desugar(field.name, obj_level);
                desugar(field.body, obj_level + 1);
            }
            for (AST *assert : ast->asserts) {
                desugar(assert, obj_level + 1);
            }

        } else if (auto *ast = dynamic_cast<Object *>(ast_)) {
            ast_ = makeObject(ast, obj_level);

        } else if (auto *ast = dynamic_cast<ObjectComprehension *>(ast_)) {
            ast_ = makeObjectComprehension(ast, obj_level);

        } else if (auto *ast = dynamic_cast<ObjectComprehensionSimple *>(ast_)) {
            desugar(ast->field, obj_level);
            desugar(ast->value, obj_level + 1);
            desugar(ast->array, obj_level);

        } else if (auto *ast = dynamic_cast<Parens *>(ast_)) {
            // Strip parens.
            desugar(ast->expr, obj_level);
            ast_ = ast->expr;

        } else if (dynamic_cast<const Self *>(ast_)) {
            // Nothing to do.

        } else if (auto *ast = dynamic_cast<SuperIndex *>(ast_)) {
            if (ast->id != nullptr) {
                assert(ast->index == nullptr);
                ast->index = str(ast->id->name);
                ast->id = nullptr;
            }
            desugar(ast->index, obj_level);

        } else if (auto *ast = dynamic_cast<Unary *>(ast_)) {
            desugar(ast->expr, obj_level);

        } else if (dynamic_cast<const Var *>(ast_)) {
            // Nothing to do.

        } else {
            std::cerr << "INTERNAL ERROR: Unknown AST: " << ast_ << std::endl;
            std::abort();
        }
    }

    void desugarFile(AST *&ast, std::map<std::string, VmExt> *tlas)
    {
        desugar(ast, 0);

        // Now, implement the std library by wrapping in a local construct.
        Tokens tokens = jsonnet_lex("std.jsonnet", STD_CODE);
        AST *std_ast = jsonnet_parse(alloc, tokens);
        desugar(std_ast, 0);
        auto *std_obj = dynamic_cast<DesugaredObject *>(std_ast);
        if (std_obj == nullptr) {
            std::cerr << "INTERNAL ERROR: std.jsonnet not an object." << std::endl;
            std::abort();
        }

        // Bind 'std' builtins that are implemented natively.
        DesugaredObject::Fields &fields = std_obj->fields;
        for (unsigned long c = 0; c <= max_builtin; ++c) {
            const auto &decl = jsonnet_builtin_decl(c);
            Identifiers params;
            for (const auto &p : decl.params)
                params.push_back(id(p));
            auto name = str(decl.name);
            auto fn = make<BuiltinFunction>(E, encode_utf8(decl.name), params);
            auto field = std::find_if(fields.begin(), fields.end(),
                [=](const DesugaredObject::Field& f) {
                    return static_cast<LiteralString*>(f.name)->value == decl.name;
                });
            if (field != fields.end()) {
                field->body = fn;
            } else {
                fields.emplace_back(ObjectField::HIDDEN, name, fn);
            }
        }
        fields.emplace_back(
            ObjectField::HIDDEN, str(U"thisFile"), str(decode_utf8(ast->location.file)));

        std::vector<std::string> empty;
        auto line_end_blank = Fodder{{FodderElement::LINE_END, 1, 0, empty}};
        auto line_end = Fodder{{FodderElement::LINE_END, 0, 0, empty}};

        // local body = ast;
        // if std.type(body) == "function") then
        //     body(tlas...)
        // else
        //     body
        if (tlas != nullptr) {
            LocationRange tla_loc("Top-level function");
            ArgParams args;
            for (const auto &pair : *tlas) {
                AST *expr;
                if (pair.second.isCode) {
                    // Now, implement the std library by wrapping in a local construct.
                    Tokens tokens = jsonnet_lex("tla:" + pair.first, pair.second.data.c_str());
                    expr = jsonnet_parse(alloc, tokens);
                    desugar(expr, 0);
                } else {
                    expr = str(decode_utf8(pair.second.data));
                }
                // Add them as named arguments, so order does not matter.
                args.emplace_back(EF, id(decode_utf8(pair.first)), EF, expr, EF);
            }
            const Identifier *body = id(U"top_level");
            ast =
                make<Local>(ast->location,
                            line_end_blank,
                            singleBind(body, ast),
                            make<Conditional>(E,
                                              line_end,
                                              primitiveEquals(E, type(var(body)), str(U"function")),
                                              EF,
                                              make<Apply>(tla_loc,
                                                          EF,
                                                          make<Var>(E, line_end, body),
                                                          EF,
                                                          args,
                                                          false,  // trailing comma
                                                          EF,
                                                          EF,
                                                          false  // tailstrict
                                                          ),
                                              line_end,
                                              make<Var>(E, line_end, body)));
        }

        // local std = (std.jsonnet stuff); ast
        ast = make<Local>(ast->location, EF, singleBind(id(U"std"), std_obj), ast);
    }
};

void jsonnet_desugar(Allocator *alloc, AST *&ast, std::map<std::string, VmExt> *tlas)
{
    Desugarer desugarer(alloc);
    desugarer.desugarFile(ast, tlas);
}