From cde3857897955558ed0e60cf8158e18d5c75d188 Mon Sep 17 00:00:00 2001
From: Florian Diebold <flodiebold@gmail.com>
Date: Sun, 4 Apr 2021 13:23:22 +0200
Subject: Add comment

---
 crates/hir_ty/src/builder.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crates/hir_ty/src/builder.rs b/crates/hir_ty/src/builder.rs
index 4d3b4eade..4a9a8058f 100644
--- a/crates/hir_ty/src/builder.rs
+++ b/crates/hir_ty/src/builder.rs
@@ -16,7 +16,10 @@ use crate::{
     TyDefId, TyKind, TypeWalk, ValueTyDefId,
 };
 
+/// This is a builder for `Ty` or anything that needs a `Substitution`.
 pub struct TyBuilder<D> {
+    /// The `data` field is used to keep track of what we're building (e.g. an
+    /// ADT, a `TraitRef`, ...).
     data: D,
     vec: SmallVec<[GenericArg; 2]>,
     param_count: usize,
-- 
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