From dca8ff5b252ce2430fa61e6a5bd230b1edc9ea50 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Thu, 3 Mar 2022 18:44:02 +0100
Subject: [PATCH] Prevent duplicate monomorphization of deserialization impls

This reduces binary size from 9.7MiB (5.8MiB for just rustbuild code)
to 9.3MiB (5.3MiB for just rustbuild code).

This doesn't reduce compile time in a statistically significant way.
---
 src/bootstrap/config.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 762f18fb32f..6e8471b1de7 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -731,7 +731,11 @@ impl Config {
 
             let contents =
                 t!(fs::read_to_string(file), format!("config file {} not found", file.display()));
-            match toml::from_str(&contents) {
+            // Deserialize to Value and then TomlConfig to prevent the Deserialize impl of
+            // TomlConfig and sub types to be monomorphized 5x by toml.
+            match toml::from_str(&contents)
+                .and_then(|table: toml::Value| TomlConfig::deserialize(table))
+            {
                 Ok(table) => table,
                 Err(err) => {
                     println!("failed to parse TOML configuration '{}': {}", file.display(), err);