tree a428186159556df0e006b6258059420ccd26b83a
parent 7374de3285b323845eb01d6b0f1aeb2b137d4023
author Brian Cairns <bcairns@google.com> 1718208117 +0000
committer Brian Cairns <bcairns@google.com> 1718208117 +0000

Add a standalone formula parser.

This is a fork of the EPPlus formula parser with all of the code that
evaluates formulas removed. AppSheet doesn't use this code as part of
its expression system, and removing it allows some significant
complexity and size reductions:

- Most of the dependencies on EPPlus Excel-specific code are
  unnecessary and have been removed
- Parsing can be a static method; there's no need for interfaces for
  everything
- There's no need for an IDisposable parser
- Many framework/NuGet dependencies are not necessary and have been
  removed

In addition, a significant amount of cleanup work has been done:
- Nullable reference types have been enabled
- Code has been generally simplified where possible
- Unnecessary interfaces have been removed

Note that this does *not* change the fundamental design or
functionality of the formula parser. Notably:
- Parsing behavior should be completely unchanged, down to whatever
  bugs the old system had
- NullReferenceException is still thrown for (some) malformed formulas
- The output is still a weird linked-list / tree hybrid
- Many functions that AppSheet doesn't support are still happily parsed

The idea is for this to be fully compatible with the existing
expression system, but faster and with fewer dependencies.

Change-Id: Ic687924a60b2673c24b39295ed684ed33d5cf9e4
Reviewed-on: https://gnocchi-internal-review.git.corp.google.com/c/third_party/epplus/+/208509
Reviewed-by: Mike Smith <mikeas@google.com>
Reviewed-by: Hughes Hilton <hugheshilton@google.com>