Introduction of expression based language

[MichaelHillcox]

This is, although relatively comprehensive, a simple expression evaluation system built around the concept of "context providers" that can optionally support namespaced methods to check against.

I've mocked in some very basic context providers for the level and the player as well as a std provider for core systems.

Out of the box we support most Java native primitive types as well as BigInts to allow builtin expression evaluation without the need for the std helpers.

This is an early concept with passing tests but I'm open to suggestions and improvements.

Right now we have 2 use cases for this. FTB Library itself can use this system for the sidebar conditionals. Then FTB Ranks can also benefit from this for it's conditional system as well. The breaking point in a new feature of Pack Companion also calls for this system so it made sense to bite the bullet and build up a more comprehensive system over the current: Define field, test field per the json specs.

[Copilot]

Pull request overview

Introduces a new expression-language subsystem (dev.ftb.mods.ftblibrary.expression) to parse and evaluate boolean expressions against pluggable, namespaced “context providers” (e.g. std.*, level.*, player.*) intended for conditional logic use-cases across FTB mods.

Changes:

• Added lexer/parser + AST node model for a small boolean expression language with comparisons and typed literals (including BigInteger).
• Added an evaluation engine and reflection-based provider invocation with basic argument coercion.
• Added baseline context providers (std, level, player) and a comprehensive JUnit test suite for parsing/evaluation.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
common/src/main/java/dev/ftb/mods/ftblibrary/expression/ExpressionEngine.java	Core entry point that parses and evaluates expressions using registered providers
common/src/main/java/dev/ftb/mods/ftblibrary/expression/ExpressionParser.java	Recursive-descent parser that produces an AST (Node)
common/src/main/java/dev/ftb/mods/ftblibrary/expression/Lexer.java	Tokenizer for identifiers, keywords, operators, strings, and numeric literals
common/src/main/java/dev/ftb/mods/ftblibrary/expression/Node.java	Sealed AST node definitions for operators, comparisons, literals, and provider calls
common/src/main/java/dev/ftb/mods/ftblibrary/expression/ProviderInvoker.java	Reflection wrapper around providers; handles method discovery, invocation, coercion
common/src/main/java/dev/ftb/mods/ftblibrary/expression/Token.java	Token record + token type enum used by lexer/parser
common/src/main/java/dev/ftb/mods/ftblibrary/expression/exceptions/ExpressionEvalException.java	Runtime exception for evaluation errors
common/src/main/java/dev/ftb/mods/ftblibrary/expression/exceptions/ExpressionParseException.java	Runtime exception for lex/parse errors
common/src/main/java/dev/ftb/mods/ftblibrary/expression/package-info.java	Applies @NullMarked to the expression package
common/src/main/java/dev/ftb/mods/ftblibrary/expression/provider/ContextProvider.java	Base class for namespaced providers
common/src/main/java/dev/ftb/mods/ftblibrary/expression/provider/StdContextProvider.java	Standard provider (std) with basic helpers like isModLoaded
common/src/main/java/dev/ftb/mods/ftblibrary/expression/provider/LevelContextProvider.java	level provider with day/night/raining helpers
common/src/main/java/dev/ftb/mods/ftblibrary/expression/provider/PlayerContextProvider.java	player provider with op/tag/name helpers (stage currently stubbed)
common/src/test/java/dev/ftb/mods/ftblibrary/expression/ExpressionEngineTest.java	Unit tests covering parsing, operators, comparisons, providers, reflection/coercion

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[desht]

Looks good to me, I added a couple of comments for trivial changes.