Migrate the backtracking code from ide_slave.ml into a new backtrack.ml.
In particular the history stack of commands that used to be there is now
non-coqide-specific.
** Adapted commands **
- "Show Script": a basic functional version is restored (and the printing
of scripts at Qed in coqtop). No indentation, one Coq command per line,
based on the vernac_expr asts recorded in the history stack, printed via
Ppvernac.
- "Back n" : now mimics the backtrack of coqide: it goes n steps back
(both commands and proofs), and maybe more if needed to avoid re-entering
a proof (it outputs a warning in this case).
- "BackTo n" : still try to go back to state n, but it also handles the
proof state, and it may end on some state n' <= n if needed to avoid
re-entering a proof. Ideally, it could someday be used by ProofGeneral
instead of the complex Backtrack command.
** Compatible commands **
- "Backtrack" is left intact from compatibility with current ProofGeneral.
We simply re-synchronize the command history stack after each Backtrack.
- "Undo" is kept as a standard command, not a backtracking one, a bit like
"Focus". Same for "Restart" and "Abort". All of these are now accepted
in coqide (Undo simply triggers a warning).
- Undocumented command "Undo To n" (counting from start of proof instead of
from end) also keep its semantics, it is simply made compatible with
the new stack mechanism.
** New restrictions **
We now forbid backtracking commands (Reset* / Back*) inside files
when Load'ing or compiling, or inside VernacList/VernacTime/VernacFail.
Too much work dealing with these situation that nobody uses.
** Internal details **
Internally, the command stack differs a bit from what was in Ide_slave
earlier (which was inspired by lisp code in ProofGeneral). We now tag
commands that are unreachable by a backtrack, due to some proof being
finished, aborted, restarted, or partly Undo'ed. This induce a bit of
bookkeeping during Qed/Abort/Restart/Undo, but then the backtracking code
is straightforward: we simply search backward the first reachable state
starting from the desired place. We don't depend anymore on the proof
names (apart in the last proof block), It's more robust this way
(think of re-entering a M.foo from an outside proof foo).
Many internal clarifications in Lib, Vernac, etc. For instance
"Reset Initial" is now just a BackTo 1, while "Reset foo" now calls
(Lib.label_before_name "foo"), and performs a BackTo to the corresponding
label.
Concerning Coqide, we directly suppress the regular printing of goals
via a flag in Vernacentries. This avoid relying on a classification
of commands in Ide_slave as earlier.
git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@15085 85f007b7-540e-0410-9357-904b9bb8a0f7