This reverts commit cce809ac90.
The code was actually correct: "expr" is never allocated when an error is
returned. This means when the expression parser fails, deleting "expr" means
deleting an uninitialized pointer.
Without clearing out the "accumulator" for the backtick parsing,
our control name was full of junk (the previous device name) causing
us to not correctly find the control.
Ensure that always we clear the "accumulator" string during backtick
parsing.
Otherwise, valid control names like "Cursor X+" would be incorrectly
tokenized as "`Cursor` `X` +", causing the parser to first abort trying to
find a control named `Cursor` rather than aborting with invalid syntax on
the bad binop.
We could also do this by resolving devices lazily, but since simple
control name bindings are going to be 90% of usecases, just look for these
first.
If an expression can't be parsed normally, we then look to see if it's a
simple device name. This keeps backwards compatibility with simple input
ocnfigurations, where people just used the Detect button.
This contains a new, hand-written expression parser to replace the old
hack language based on string munging. The new approach is a simple
AST-based evaluation approach, instead of the "list of operations"
infix-based hack that there was before.
The new language for configuration has support for parentheses, and
counts "!" as a unary operator instead of the binary "NOT OR" operator
it was before. A simple example:
(X & Y) | !B
Explicit device references, and complex device names ("Right Y+") are
handled with backticks and colons:
(`SDL/0/6 axis joystick:Right X+` & `DInput/0/Keyboard Mouse:A`)
The basic editor UI that inserts tokens has not been updated to reflect
the new language.
