Implement HIR builder

[DaniPopes]

Describe the feature

Implement a HIR builder that constructs HIR nodes using a bunch of helper methods.

Example:

pub struct HirBuilder<'hir> { /* ... */ }
impl<'hir> HirBuilder<'hir> {
    pub fn expr(&self, kind: hir::ExprKind<'hir>) -> hir::Expr<'hir> { /* ... */ }
}

An initial goal for this would be to replace the manual HIR node construction when desugaring loops and creating variables' getter functions, adding the necessary methods along the way.

Additional context

No response

[ftupas]

Hi there, can i take a crack at this?

[mahmudsudo]

Can I take on this if still available ?

[gakonst]

hey @ftupas any update here? also would love for people to describe the solution they want to design before asking for taking it!

[ftupas]

@gakonst hi sorry for the delay, got a bit busy with work and not sure if I will have bandwidth in the coming days. I think it's best to unassign me so someone can pick it up

[mahmudsudo]

@gakonst Here's how I'm thinking about implementing the HIR builder:

pub struct HirBuilder<'hir> {
    arena: &'hir Arena<'hir>,
    def_id: DefId,
    // Additional context like symbol tables etc.
}
impl<'hir> HirBuilder<'hir> {
    // Core node construction
    pub fn expr(&self, kind: ExprKind<'hir>) -> Expr<'hir> {
        // Allocate in arena and return new expression
    }
    
    // Common expression builders
    pub fn literal(&self, lit: Literal) -> Expr<'hir> {
        self.expr(ExprKind::Lit(lit))
    }
    
    pub fn block(&self, stmts: Vec<Stmt<'hir>>, expr: Option<Expr<'hir>>) -> Expr<'hir> {
        self.expr(ExprKind::Block(stmts, expr))
    }

    // Methods specifically for loops and getters
    pub fn loop_expr(&self, body: Expr<'hir>) -> Expr<'hir> {
        // Construct loop expression with proper labels/blocks
    }

    pub fn getter_fn(&self, field: &Field) -> Expr<'hir> {
        // Construct getter function body
    }
}