Before, the termination argument as inferred by `GuessLex` was passed
further
on as `Syntax`, to be elaborated later in `WF.Rel`.
This didn’t feel quite right anymore. In particular if we want to teach
`GuessLex` about guessing more complex termination arguments like
`xs.size -
i`, using `Expr` here is more natural.
So this introduces `TerminationArgument` based on an `Expr` to be used
here.
A side-effect of how the termination arguments are elaborated is that
the unused
variables linter will now look at `termination_by` variables, and that
parameters
past the colon are not even invisibly in scope, so `‹_›` will not find
them
See https://github.com/leanprover-community/mathlib4/pull/11370/files
for examples
of fixing these changes.
This introduces the `ArgsPacker` module and abstraction, to replace the
exising `PackDomain`/`PackMutual` code. The motivation was that we now
have more uses besides `Fix.lean` (`GuessLex` and `FunInd`), and the
code was spread in various places.
The goals are
* consistent function naming withing the the `PSigma` handling, the
`PSum` handling, and the combined interface
* avoid taking a type apart just based on the `PSigma`/`PSum` nesting,
to be robust in case the user happens to be using `PSigma`/`PSum`
somewhere. Therefore, always pass an `arity` or `numFuncs` or `varNames`
around.
* keep all the `PSigma`/`PSum` encoding logic contained within one
module (`ArgsPacker`), and keep that module independent of its users (so
no `EqnInfos` visible here).
* pick good variable names when matching on a packed argument
* the unary function now is either called `fun1._unary` or
`fun1._mutual`, never `fun1._unary._mutual`.
This file has less heavy dependencies than `PackMutual` had, so build
parallelism is improved as well.
