This PR improves the error messages produced by the `split` tactic,
including suggesting syntax fixes and related tactics with which it
might be confused.
Note that, to avoid clashing with the new error message styling
conventions used in these messages, this PR also updates the formatting
of the message produced by `throwTacticEx`.
Closes#6224
This PR makes `#guard_msgs` to treat `trace` messages separate from
`info`, `warning` and `error`. It also introduce the ability to say
`#guard_msgs (pass info`, like `(drop info)` so far, and also adds
`(check info)` as the explicit form of `(info)`, for completeness.
Fixes#8266
This PR implements tactics called `extract_lets` and `lift_lets` that
manipulate `let`/`let_fun` expressions. The `extract_lets` tactic
creates new local declarations extracted from any `let` and `let_fun`
expressions in the main goal. For top-level lets in the target, it is
like the `intros` tactic, but in general it can extract lets from deeper
subexpressions as well. The `lift_lets` tactic moves `let` and `let_fun`
expressions as far out of an expression as possible, but it does not
extract any new local declarations. The option `extract_lets +lift`
combines these behaviors.
This is a re-implementation of `extract_lets` and `lift_lets` from
mathlib. The new `extract_lets` is like doing `lift_lets; extract_lets`,
but it does not lift unextractable lets like `lift_lets`. The
`lift_lets; extract_lets` behavior is now handled by `extract_lets
+lift`. The new `lift_lets` tactic is a frontend to `extract_lets +lift`
machinery, which rather than creating new local definitions instead
represents the accumulated local declarations as top-level lets.
There are also conv tactics for both of these. The `extract_lets` has a
limitation due to the conv architecture; it can extract lets for a given
conv goal, but the local declarations don't survive outside conv. They
get zeta reduced immediately upon leaving conv.
