Mercurial > hg
view mercurial/linelog.py @ 38795:422d661056be
linelog: add a Python implementation of the linelog datastructure
This datastructure was originally developed by Jun Wu at Facebook,
inspired by SCCS weaves. It's useful as a cache for blame information,
but also is the magic that makes `hg absorb` easy to implement. In
service of importing the code to Mercurial, I wanted to actually
/understand/ it, and once I did I decided to take a run at
implementing it.
The help/internals/linelog.txt document is the README from Jun Wu's
implementaiton. It all applies to our linelog implementation.
Differential Revision: https://phab.mercurial-scm.org/D3990
author | Augie Fackler <augie@google.com> |
---|---|
date | Mon, 30 Jul 2018 10:42:37 -0400 |
parents | |
children | f956dc7217fc |
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# linelog - efficient cache for annotate data # # Copyright 2018 Google LLC. # # This software may be used and distributed according to the terms of the # GNU General Public License version 2 or any later version. """linelog is an efficient cache for annotate data inspired by SCCS Weaves. SCCS Weaves are an implementation of https://en.wikipedia.org/wiki/Interleaved_deltas. See mercurial/help/internals/linelog.txt for an exploration of SCCS weaves and how linelog works in detail. Here's a hacker's summary: a linelog is a program which is executed in the context of a revision. Executing the program emits information about lines, including the revision that introduced them and the line number in the file at the introducing revision. When an insertion or deletion is performed on the file, a jump instruction is used to patch in a new body of annotate information. """ from __future__ import absolute_import, print_function import abc import struct from mercurial import ( pycompat, ) from .thirdparty import ( attr, ) _llentry = struct.Struct('>II') class LineLogError(Exception): """Error raised when something bad happens internally in linelog.""" @attr.s class lineinfo(object): # Introducing revision of this line. rev = attr.ib() # Line number for this line in its introducing revision. linenum = attr.ib() # Private. Offset in the linelog program of this line. Used internally. _offset = attr.ib() @attr.s class annotateresult(object): rev = attr.ib() lines = attr.ib() _eof = attr.ib() def __iter__(self): return iter(self.lines) class _llinstruction(object): __metaclass__ = abc.ABCMeta @abc.abstractmethod def __init__(self, op1, op2): pass @abc.abstractmethod def __str__(self): pass def __repr__(self): return str(self) @abc.abstractmethod def __eq__(self, other): pass @abc.abstractmethod def encode(self): """Encode this instruction to the binary linelog format.""" @abc.abstractmethod def execute(self, rev, pc, emit): """Execute this instruction. Args: rev: The revision we're annotating. pc: The current offset in the linelog program. emit: A function that accepts a single lineinfo object. Returns: The new value of pc. Returns None if exeuction should stop (that is, we've found the end of the file.) """ class _jge(_llinstruction): """If the current rev is greater than or equal to op1, jump to op2.""" def __init__(self, op1, op2): self._cmprev = op1 self._target = op2 def __str__(self): return 'JGE %d %d' % (self._cmprev, self._target) def __eq__(self, other): return (type(self) == type(other) and self._cmprev == other._cmprev and self._target == other._target) def encode(self): return _llentry.pack(self._cmprev << 2, self._target) def execute(self, rev, pc, emit): if rev >= self._cmprev: return self._target return pc + 1 class _jump(_llinstruction): """Unconditional jumps are expressed as a JGE with op1 set to 0.""" def __init__(self, op1, op2): if op1 != 0: raise LineLogError("malformed JUMP, op1 must be 0, got %d" % op1) self._target = op2 def __str__(self): return 'JUMP %d' % (self._target) def __eq__(self, other): return (type(self) == type(other) and self._target == other._target) def encode(self): return _llentry.pack(0, self._target) def execute(self, rev, pc, emit): return self._target class _eof(_llinstruction): """EOF is expressed as a JGE that always jumps to 0.""" def __init__(self, op1, op2): if op1 != 0: raise LineLogError("malformed EOF, op1 must be 0, got %d" % op1) if op2 != 0: raise LineLogError("malformed EOF, op2 must be 0, got %d" % op2) def __str__(self): return 'EOF' def __eq__(self, other): return type(self) == type(other) def encode(self): return _llentry.pack(0, 0) def execute(self, rev, pc, emit): return None class _jl(_llinstruction): """If the current rev is less than op1, jump to op2.""" def __init__(self, op1, op2): self._cmprev = op1 self._target = op2 def __str__(self): return 'JL %d %d' % (self._cmprev, self._target) def __eq__(self, other): return (type(self) == type(other) and self._cmprev == other._cmprev and self._target == other._target) def encode(self): return _llentry.pack(1 | (self._cmprev << 2), self._target) def execute(self, rev, pc, emit): if rev < self._cmprev: return self._target return pc + 1 class _line(_llinstruction): """Emit a line.""" def __init__(self, op1, op2): # This line was introduced by this revision number. self._rev = op1 # This line had the specified line number in the introducing revision. self._origlineno = op2 def __str__(self): return 'LINE %d %d' % (self._rev, self._origlineno) def __eq__(self, other): return (type(self) == type(other) and self._rev == other._rev and self._origlineno == other._origlineno) def encode(self): return _llentry.pack(2 | (self._rev << 2), self._origlineno) def execute(self, rev, pc, emit): emit(lineinfo(self._rev, self._origlineno, pc)) return pc + 1 def _decodeone(data, offset): """Decode a single linelog instruction from an offset in a buffer.""" try: op1, op2 = _llentry.unpack_from(data, offset) except struct.error as e: raise LineLogError('reading an instruction failed: %r' % e) opcode = op1 & 0b11 op1 = op1 >> 2 if opcode == 0: if op1 == 0: if op2 == 0: return _eof(op1, op2) return _jump(op1, op2) return _jge(op1, op2) elif opcode == 1: return _jl(op1, op2) elif opcode == 2: return _line(op1, op2) raise NotImplementedError('Unimplemented opcode %r' % opcode) class linelog(object): """Efficient cache for per-line history information.""" def __init__(self, program=None, maxrev=0): if program is None: # We pad the program with an extra leading EOF so that our # offsets will match the C code exactly. This means we can # interoperate with the C code. program = [_eof(0, 0), _eof(0, 0)] self._program = program self._lastannotate = None self._maxrev = maxrev def __eq__(self, other): return (type(self) == type(other) and self._program == other._program and self._maxrev == other._maxrev) def __repr__(self): return '<linelog at %s: maxrev=%d size=%d>' % ( hex(id(self)), self._maxrev, len(self._program)) def debugstr(self): fmt = '%%%dd %%s' % len(str(len(self._program))) return '\n'.join( fmt % (idx, i) for idx, i in enumerate(self._program[1:], 1)) @classmethod def fromdata(cls, buf): if len(buf) % _llentry.size != 0: raise LineLogError( "invalid linelog buffer size %d (must be a multiple of %d)" % ( len(buf), _llentry.size)) expected = len(buf) / _llentry.size fakejge = _decodeone(buf, 0) if isinstance(fakejge, _jump): maxrev = 0 else: maxrev = fakejge._cmprev numentries = fakejge._target if expected != numentries: raise LineLogError("corrupt linelog data: claimed" " %d entries but given data for %d entries" % ( expected, numentries)) instructions = [_eof(0, 0)] for offset in pycompat.xrange(1, numentries): instructions.append(_decodeone(buf, offset * _llentry.size)) return cls(instructions, maxrev=maxrev) def encode(self): hdr = _jge(self._maxrev, len(self._program)).encode() return hdr + ''.join(i.encode() for i in self._program[1:]) def clear(self): self._program = [] self._maxrev = 0 self._lastannotate = None def replacelines(self, rev, a1, a2, b1, b2): """Replace lines [a1, a2) with lines [b1, b2).""" if self._lastannotate: # TODO(augie): make replacelines() accept a revision at # which we're editing as well as a revision to mark # responsible for the edits. In hg-experimental it's # stateful like this, so we're doing the same thing to # retain compatibility with absorb until that's imported. ar = self._lastannotate else: ar = self.annotate(rev) # ar = self.annotate(self._maxrev) if a1 > len(ar.lines): raise LineLogError( '%d contains %d lines, tried to access line %d' % ( rev, len(ar.lines), a1)) elif a1 == len(ar.lines): # Simulated EOF instruction since we're at EOF, which # doesn't have a "real" line. a1inst = _eof(0, 0) a1info = lineinfo(0, 0, ar._eof) else: a1info = ar.lines[a1] a1inst = self._program[a1info._offset] oldproglen = len(self._program) appendinst = self._program.append # insert if b1 < b2: # Determine the jump target for the JGE at the start of # the new block. tgt = oldproglen + (b2 - b1 + 1) # Jump to skip the insert if we're at an older revision. appendinst(_jl(rev, tgt)) for linenum in pycompat.xrange(b1, b2): appendinst(_line(rev, linenum)) # delete if a1 < a2: if a2 > len(ar.lines): raise LineLogError( '%d contains %d lines, tried to access line %d' % ( rev, len(ar.lines), a2)) elif a2 == len(ar.lines): endaddr = ar._eof else: endaddr = ar.lines[a2]._offset if a2 > 0 and rev < self._maxrev: # If we're here, we're deleting a chunk of an old # commit, so we need to be careful and not touch # invisible lines between a2-1 and a2 (IOW, lines that # are added later). endaddr = ar.lines[a2 - 1]._offset + 1 appendinst(_jge(rev, endaddr)) # copy instruction from a1 appendinst(a1inst) # if a1inst isn't a jump or EOF, then we need to add an unconditional # jump back into the program here. if not isinstance(a1inst, (_jump, _eof)): appendinst(_jump(0, a1info._offset + 1)) # Patch instruction at a1, which makes our patch live. self._program[a1info._offset] = _jump(0, oldproglen) # For compat with the C version, re-annotate rev so that # self.annotateresult is cromulent.. We could fix up the # annotateresult in place (which is how the C version works), # but for now we'll pass on that and see if it matters in # practice. self.annotate(max(self._lastannotate.rev, rev)) if rev > self._maxrev: self._maxrev = rev def annotate(self, rev): pc = 1 lines = [] # Sanity check: if len(lines) is longer than len(program), we # hit an infinite loop in the linelog program somehow and we # should stop. while pc is not None and len(lines) < len(self._program): inst = self._program[pc] lastpc = pc pc = inst.execute(rev, pc, lines.append) if pc is not None: raise LineLogError( 'Probably hit an infinite loop in linelog. Program:\n' + self.debugstr()) ar = annotateresult(rev, lines, lastpc) self._lastannotate = ar return ar @property def maxrev(self): return self._maxrev # Stateful methods which depend on the value of the last # annotation run. This API is for compatiblity with the original # linelog, and we should probably consider refactoring it. @property def annotateresult(self): """Return the last annotation result. C linelog code exposed this.""" return [(l.rev, l.linenum) for l in self._lastannotate.lines] def getoffset(self, line): return self._lastannotate.lines[line]._offset def getalllines(self, start=0, end=0): """Get all lines that ever occurred in [start, end). Passing start == end == 0 means "all lines ever". This works in terms of *internal* program offsets, not line numbers. """ pc = start or 1 lines = [] # only take as many steps as there are instructions in the # program - if we don't find an EOF or our stop-line before # then, something is badly broken. for step in pycompat.xrange(len(self._program)): inst = self._program[pc] nextpc = pc + 1 if isinstance(inst, _jump): nextpc = inst._target elif isinstance(inst, _eof): return lines elif isinstance(inst, (_jl, _jge)): pass elif isinstance(inst, _line): lines.append((inst._rev, inst._origlineno)) else: raise LineLogError("Illegal instruction %r" % inst) if nextpc == end: return lines pc = nextpc raise LineLogError("Failed to perform getalllines")