feat: Implement traits - parser support #2094

[yordanmadzhunkov]

Description

Parser support for traits

• The functions within trait definitions can now have a body ( Expand trait definition in AST to include body )
• Parsing support for trait-associated constants (using the let keyword for now to avoid introducing a new keyword such as const).
• Traits can have a where clause
• The where clause is only allowed on generic definitions
• The parsing of where clauses with multiple constraints has been fixed
• More parsing tests for functions using traits and trait definitions.
• Parser tests now pass by ignore warnings

Problem*

After the first prototype of traits implementation we agreed to split into small PRs and merge them one by one in master branch.
This is the first from many to follow. Enjoy

Resolves

Summary*

After this PR the parser with parse ( with traits are experimental warnings ) the following code

trait Empty {}

trait TraitWithDefaultBody { fn foo(self) {}; }

trait TraitAcceptingMutableRef { fn foo(&mut self); }

trait TraitWithTypeBoundOperation { fn identity() -> Self; }

trait TraitWithAssociatedType { type Element; fn item(self, index: Field) -> Self::Element; }

trait TraitWithAssociatedConstant { let Size: Field; }

trait TraitWithAssociatedConstantWithDefaultValue { let Size: Field = 10; }

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[yordanmadzhunkov]

@jfecher

[jfecher]

Looks mostly good, but lets revert the changed error check for no longer disallowing patterns in trait parameters. To match rust we should always disallow them.

[jfecher]

Looks good. My bad for holding this up 👍