rust/src/etc/gdb_rust_pretty_printing.py

# Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
# file at the top-level directory of this distribution and at
# http://rust-lang.org/COPYRIGHT.
#
# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
# option. This file may not be copied, modified, or distributed
# except according to those terms.

import gdb

#===============================================================================
# GDB Pretty Printing Module for Rust
#===============================================================================


def register_printers(objfile):
    "Registers Rust pretty printers for the given objfile"
    objfile.pretty_printers.append(rust_pretty_printer_lookup_function)


def rust_pretty_printer_lookup_function(val):
    "Returns the correct Rust pretty printer for the given value if there is one"
    type_code = val.type.code

    if type_code == gdb.TYPE_CODE_STRUCT:
        struct_kind = classify_struct(val.type)

        if struct_kind == STRUCT_KIND_STR_SLICE:
            return RustStringSlicePrinter(val)

        if struct_kind == STRUCT_KIND_TUPLE:
            return RustTuplePrinter(val)

        if struct_kind == STRUCT_KIND_TUPLE_STRUCT:
            return RustTupleStructPrinter(val, False)

        if struct_kind == STRUCT_KIND_CSTYLE_VARIANT:
            return RustCStyleEnumPrinter(val[get_field_at_index(val, 0)])

        if struct_kind == STRUCT_KIND_TUPLE_VARIANT:
            return RustTupleStructPrinter(val, True)

        if struct_kind == STRUCT_KIND_STRUCT_VARIANT:
            return RustStructPrinter(val, True)

        return RustStructPrinter(val, False)

    # Enum handling
    if type_code == gdb.TYPE_CODE_UNION:
        enum_members = list(val.type.fields())
        enum_member_count = len(enum_members)

        if enum_member_count == 0:
            return RustStructPrinter(val, False)

        if enum_member_count == 1:
            first_variant_name = enum_members[0].name
            if first_variant_name is None:
                # This is a singleton enum
                return rust_pretty_printer_lookup_function(val[enum_members[0]])
            else:
                assert first_variant_name.startswith("RUST$ENCODED$ENUM$")
                # This is a space-optimized enum.
                # This means this enum has only two states, and Rust uses one
                # of the fields somewhere in the struct to determine which of
                # the two states it's in. The location of the field is encoded
                # in the name as something like
                # RUST$ENCODED$ENUM$(num$)*name_of_zero_state
                last_separator_index = first_variant_name.rfind("$")
                start_index = len("RUST$ENCODED$ENUM$")
                disr_field_indices = first_variant_name[start_index:last_separator_index].split("$")
                disr_field_indices = [int(index) for index in disr_field_indices]

                sole_variant_val = val[enum_members[0]]
                discriminant = sole_variant_val
                for disr_field_index in disr_field_indices:
                    disr_field = get_field_at_index(discriminant, disr_field_index)
                    discriminant = discriminant[disr_field]

                # If the discriminant field is a fat pointer we have to consider the
                # first word as the true discriminant
                if discriminant.type.code == gdb.TYPE_CODE_STRUCT:
                    discriminant = discriminant[get_field_at_index(discriminant, 0)]

                if discriminant == 0:
                    null_variant_name = first_variant_name[last_separator_index + 1:]
                    return IdentityPrinter(null_variant_name)

                return rust_pretty_printer_lookup_function(sole_variant_val)

        # This is a regular enum, extract the discriminant
        discriminant_name, discriminant_val = extract_discriminant_value(val)
        return rust_pretty_printer_lookup_function(val[enum_members[discriminant_val]])

    # No pretty printer has been found
    return None

#=------------------------------------------------------------------------------
# Pretty Printer Classes
#=------------------------------------------------------------------------------


class RustStructPrinter:
    def __init__(self, val, hide_first_field):
        self.val = val
        self.hide_first_field = hide_first_field

    def to_string(self):
        return self.val.type.tag

    def children(self):
        cs = []
        for field in self.val.type.fields():
            field_name = field.name
            # Normally the field name is used as a key to access the field
            # value, because that's also supported in older versions of GDB...
            field_key = field_name
            if field_name is None:
                field_name = ""
                # ... but for fields without a name (as in tuples), we have to
                # fall back to the newer method of using the field object
                # directly as key. In older versions of GDB, this will just
                # fail.
                field_key = field
            name_value_tuple = (field_name, self.val[field_key])
            cs.append(name_value_tuple)

        if self.hide_first_field:
            cs = cs[1:]

        return cs


class RustTuplePrinter:
    def __init__(self, val):
        self.val = val

    def to_string(self):
        return None

    def children(self):
        cs = []
        for field in self.val.type.fields():
            cs.append(("", self.val[field]))

        return cs

    def display_hint(self):
        return "array"


class RustTupleStructPrinter:
    def __init__(self, val, hide_first_field):
        self.val = val
        self.hide_first_field = hide_first_field

    def to_string(self):
        return self.val.type.tag

    def children(self):
        cs = []
        for field in self.val.type.fields():
            cs.append(("", self.val[field]))

        if self.hide_first_field:
            cs = cs[1:]

        return cs

    def display_hint(self):
        return "array"


class RustStringSlicePrinter:
    def __init__(self, val):
        self.val = val

    def to_string(self):
        slice_byte_len = self.val["length"]
        return '"%s"' % self.val["data_ptr"].string(encoding="utf-8", length=slice_byte_len)


class RustCStyleEnumPrinter:
    def __init__(self, val):
        assert val.type.code == gdb.TYPE_CODE_ENUM
        self.val = val

    def to_string(self):
        return str(self.val)


class IdentityPrinter:
    def __init__(self, string):
        self.string = string

    def to_string(self):
        return self.string

STRUCT_KIND_REGULAR_STRUCT  = 0
STRUCT_KIND_TUPLE_STRUCT    = 1
STRUCT_KIND_TUPLE           = 2
STRUCT_KIND_TUPLE_VARIANT   = 3
STRUCT_KIND_STRUCT_VARIANT  = 4
STRUCT_KIND_CSTYLE_VARIANT  = 5
STRUCT_KIND_STR_SLICE       = 6


def classify_struct(type):
    if type.tag == "&str":
        return STRUCT_KIND_STR_SLICE

    fields = list(type.fields())
    field_count = len(fields)

    if field_count == 0:
        return STRUCT_KIND_REGULAR_STRUCT

    if fields[0].name == "RUST$ENUM$DISR":
        if field_count == 1:
            return STRUCT_KIND_CSTYLE_VARIANT
        elif fields[1].name is None:
            return STRUCT_KIND_TUPLE_VARIANT
        else:
            return STRUCT_KIND_STRUCT_VARIANT

    if fields[0].name is None:
        if type.tag.startswith("("):
            return STRUCT_KIND_TUPLE
        else:
            return STRUCT_KIND_TUPLE_STRUCT

    return STRUCT_KIND_REGULAR_STRUCT


def extract_discriminant_value(enum_val):
    assert enum_val.type.code == gdb.TYPE_CODE_UNION
    for variant_descriptor in enum_val.type.fields():
        variant_val = enum_val[variant_descriptor]
        for field in variant_val.type.fields():
            return (field.name, int(variant_val[field]))


def first_field(val):
    for field in val.type.fields():
        return field


def get_field_at_index(val, index):
    i = 0
    for field in val.type.fields():
        if i == index:
            return field
        i += 1
    return None