Instantiate body instead of using ParamTypeMapper

[coord-e]

follow-up of #8 for #10

Translating ParamTy in TypeBuilder (via ParamTypeMapper) is insufficient for resolving traits in #10 because the actual GenericArgs are unknown when typing function calls.

In the call to generic within the following example, def_ty_with_args attempts to check generic using int as a type argument (note: this is not i32, as it is already converted to rty::Type). However, BasicBlockAnalyzer unable to find the DefId of <i32 as Trait>::t because it only knows that T=int, but does not know T=i32, making it impossible to use Instance::resolve with fully substituted type arguments (i32 here).

trait Trait {
  fn t(self);
}

impl Trait for i32 {
  fn t(self) { assert!(self != 0); }
}

fn generic<T: Trait>(x: T) {
  x.t()
}

fn main() {
  generic(1_i32);
}

[Copilot]

Pull request overview

This PR implements body substitution for generic functions to enable proper trait resolution. Instead of using a ParamTypeMapper to translate type parameters symbolically, the PR substitutes the MIR body with concrete generic arguments (e.g., i32), allowing trait method resolution to work correctly when analyzing generic functions with trait bounds.

Key Changes:

• Replace the ParamTypeMapper approach with direct MIR body substitution using EarlyBinder::instantiate
• Update def_ty_with_args to work with mir_ty::GenericArgsRef instead of rty::TypeArgs
• Add placeholder_generic_args method to generate placeholder arguments for generic functions during analysis

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/rty.rs	Remove Hash and PartialEq derives from types that don't need them; remove TypeArgs from public API
src/refine/template.rs	Remove ParamTypeMapper trait and related machinery; simplify translate_param_type
src/chc.rs	Remove Hash and PartialEq derives from CHC types
src/analyze.rs	Update caching to use GenericArgsRef; add local_fn_sig_with_body helper method
src/analyze/crate_.rs	Replace type_builder with generic_args approach; add placeholder_generic_args method
src/analyze/local_def.rs	Update to use local_fn_sig_with_body; add generic_args method for body substitution
src/analyze/basic_block.rs	Simplify function call type resolution to pass GenericArgsRef directly

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