Deduplication: Pulled common logic out from lower_const_arg_struct

[LaneAsade]

This PR aims to deduplicate the logic in the function lower_const_arg_struct by creating a helper function lower_path_for_struct_expr which is shared between rustc_hir_ty_lowering and rustc_hir_typeck.

Related: #150621

Helper function code:

pub struct ResolvedStructPath<'tcx> {
    pub res: Result<Res, ErrorGuaranteed>,
    pub ty: Ty<'tcx>,
}

pub fn lower_path_for_struct_expr(
        &self,
        qpath: hir::QPath<'tcx>,
        path_span: Span,
        hir_id: HirId,
    ) -> ResolvedStructPath<'tcx> {
        match qpath {
            hir::QPath::Resolved(ref maybe_qself, path) => {
                let self_ty = maybe_qself.as_ref().map(|qself| self.lower_ty(qself));
                let ty = self.lower_resolved_ty_path(self_ty, path, hir_id, PermitVariants::Yes);
                ResolvedStructPath { res: Ok(path.res), ty }
            }
            hir::QPath::TypeRelative(hir_self_ty, segment) => {
                let self_ty = self.lower_ty(hir_self_ty);

                let result = self.lower_type_relative_ty_path(
                    self_ty,
                    hir_self_ty,
                    segment,
                    hir_id,
                    path_span,
                    PermitVariants::Yes,
                );
                let ty = result
                    .map(|(ty, _, _)| ty)
                    .unwrap_or_else(|guar| Ty::new_error(self.tcx(), guar));

                ResolvedStructPath {
                    res: result.map(|(_, kind, def_id)| Res::Def(kind, def_id)),
                    ty,
                }
            }
        }
    }

Thanks to @BoxyUwU for the guidance on this issue.

[rustbot]

HIR ty lowering was modified

cc @fmease

[rustbot]

r? @chenyukang

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• Owners of files modified in this PR: compiler, types
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[rustbot]

⚠️ Warning ⚠️

• This PR is based on an upstream commit that is older than 28 days.

  It's recommended to update your branch according to the rustc-dev-guide.

[Human9000-bit]

cc @BoxyUwU

[BoxyUwU]

r? BoxyUwU

[BoxyUwU]

thx, sorry for taking so long to review this.

@bors r+ rollup=iffy

[rust-bors]

📌 Commit fc157f6 has been approved by BoxyUwU

It is now in the queue for this repository.