execer.py

"""Implements the xonsh executer"""
import re
import os
import types
import inspect
import builtins
from collections import Iterable, Sequence, Mapping

from xonsh import ast
from xonsh.parser import Parser
from xonsh.tools import subproc_toks
from xonsh.built_ins import load_builtins, unload_builtins


class Execer(object):
    """Executes xonsh code in a context."""

    def __init__(self,
                 filename='<xonsh-code>',
                 debug_level=0,
                 parser_args=None,
                 unload=True):
        """Parameters
        ----------
        filename : str, optional
            File we are to execute.
        debug_level : int, optional
            Debugging level to use in lexing and parsing.
        parser_args : dict, optional
            Arguments to pass down to the parser.
        unload : bool, optional
            Whether or not to unload xonsh builtins upon deletion.
        """
        parser_args = parser_args or {}
        self.parser = Parser(**parser_args)
        self.filename = filename
        self.debug_level = debug_level
        self.unload = unload
        self.ctxtransformer = ast.CtxAwareTransformer(self.parser)
        load_builtins(execer=self)

    def __del__(self):
        if self.unload:
            unload_builtins()

    def parse(self, input, ctx, mode='exec'):
        """Parses xonsh code in a context-aware fashion. For context-free
        parsing, please use the Parser class directly.
        """
        if ctx is None:
            ctx = set()
        elif isinstance(ctx, Mapping):
            ctx = set(ctx.keys())

        # Parsing actually happens in a couple of phases. The first is a
        # shortcut for a context-free parser. Normally, all subprocess
        # lines should be wrapped in $(), to indicate that they are a
        # subproc. But that would be super annoying. Unfortnately, Python
        # mode - after indentation - is whitespace agnostic while, using
        # the Python token, subproc mode is whitespace aware. That is to say,
        # in Python mode "ls -l", "ls-l", and "ls - l" all parse to the
        # same AST because whitespace doesn't matter to the minus binary op.
        # However, these phases all have very different meaning in subproc
        # mode. The 'right' way to deal with this is to make the entire
        # grammar whitespace aware, and then ignore all of the whitespace
        # tokens for all of the Python rules. The lazy way implemented here
        # is to parse a line a second time with a $() wrapper if it fails
        # the first time. This is a context-free phase.
        tree = self._parse_ctx_free(input, mode=mode)
        if tree is None:
            return None

        # Now we need to perform context-aware AST transformation. This is
        # because the "ls -l" is valid Python. The only way that we know
        # it is not actually Python is by checking to see if the first token
        # (ls) is part of the execution context. If it isn't, then we will
        # assume that this line is supposed to be a subprocess line, assuming
        # it also is valid as a subprocess line.
        tree = self.ctxtransformer.ctxvisit(tree, input, ctx, mode=mode)
        return tree

    def compile(self, input, mode='exec', glbs=None, locs=None, stacklevel=2,
                filename=None):
        """Compiles xonsh code into a Python code object, which may then
        be execed or evaled.
        """
        if filename is None:
            filename = self.filename
        if glbs is None or locs is None:
            frame = inspect.stack()[stacklevel][0]
            glbs = frame.f_globals if glbs is None else glbs
            locs = frame.f_locals if locs is None else locs
        ctx = set(dir(builtins)) | set(glbs.keys()) | set(locs.keys())
        tree = self.parse(input, ctx, mode=mode)
        if tree is None:
            return None  # handles comment only input
        code = compile(tree, filename, mode)
        return code

    def eval(self, input, glbs=None, locs=None, stacklevel=2):
        """Evaluates (and returns) xonsh code."""
        if isinstance(input, types.CodeType):
            code = input
        else:
            code = self.compile(input=input,
                                glbs=glbs,
                                locs=locs,
                                mode='eval',
                                stacklevel=stacklevel)
        if code is None:
            return None  # handles comment only input
        return eval(code, glbs, locs)

    def exec(self, input, mode='exec', glbs=None, locs=None, stacklevel=2):
        """Execute xonsh code."""
        if isinstance(input, types.CodeType):
            code = input
        else:
            code = self.compile(input=input,
                                glbs=glbs,
                                locs=locs,
                                mode=mode,
                                stacklevel=stacklevel)
        if code is None:
            return None  # handles comment only input
        return exec(code, glbs, locs)

    def _find_next_break(self, line, mincol):
        if mincol >= 1:
            line = line[mincol:]
        if ';' not in line:
            return None
        maxcol = None
        self.parser.lexer.input(line)
        for tok in self.parser.lexer:
            if tok.type == 'SEMI':
                maxcol = tok.lexpos + mincol + 1
                break
        return maxcol

    def _parse_ctx_free(self, input, mode='exec'):
        last_error_line = last_error_col = -1
        parsed = False
        original_error = None
        while not parsed:
            try:
                tree = self.parser.parse(input,
                                         filename=self.filename,
                                         mode=mode,
                                         debug_level=self.debug_level)
                parsed = True
            except IndentationError as e:
                if original_error is None:
                    raise e
                else:
                    raise original_error
            except SyntaxError as e:
                if original_error is None:
                    original_error = e
                if (e.loc is None) or (last_error_line == e.loc.lineno and
                                       last_error_col in (e.loc.column + 1,
                                                          e.loc.column)):
                    raise original_error
                last_error_col = e.loc.column
                last_error_line = e.loc.lineno
                idx = last_error_line - 1
                lines = input.splitlines()
                line = lines[idx]
                if input.endswith('\n'):
                    lines.append('')
                if len(line.strip()) == 0:
                    # whitespace only lines are not valid syntax in Python's
                    # interactive mode='single', who knew?! Just ignore them.
                    # this might cause actual sytax errors to have bad line
                    # numbers reported, but should only effect interactive mode
                    del lines[idx]
                    last_error_line = last_error_col = -1
                    input = '\n'.join(lines)
                    continue

                if last_error_line > 1 and lines[idx-1].rstrip()[-1:] == ':':
                    # catch non-indented blocks and raise error.
                    prev_indent = len(lines[idx-1]) - len(lines[idx-1].lstrip())
                    curr_indent = len(lines[idx]) - len(lines[idx].lstrip())
                    if prev_indent == curr_indent:
                        raise original_error
                maxcol = self._find_next_break(line, last_error_col)
                sbpline = subproc_toks(line,
                                       returnline=True,
                                       maxcol=maxcol,
                                       lexer=self.parser.lexer)
                if sbpline is None:
                    # subprocess line had no valid tokens, likely because
                    # it only contained a comment.
                    del lines[idx]
                    last_error_line = last_error_col = -1
                    input = '\n'.join(lines)
                    continue
                else:
                    lines[idx] = sbpline
                last_error_col += 3
                input = '\n'.join(lines)
        return tree