From 4d879662a9ef1184fa9f35d43bedd4b451e659c7 Mon Sep 17 00:00:00 2001
From: Michael Killough <michaeljkillough@gmail.com>
Date: Tue, 16 May 2017 18:05:40 +0700
Subject: [PATCH] Track which config items are accessed.

Required by #865. This doesn't introduce any method to view which
parameters are accessed.

We record which config items are accessed even if we don't intend to
output them, as we assume it will be a relatively cheap operation.
---
 src/config.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/config.rs b/src/config.rs
index 63c33cdf6fc1..44c40f2ac6cb 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -10,6 +10,8 @@
 
 extern crate toml;
 
+use std::cell::RefCell;
+use std::collections::HashSet;
 use std::error;
 use std::result;
 
@@ -211,10 +213,34 @@ impl ConfigHelpItem {
     }
 }
 
+/// This is used by Config to track which config parameters are accessed during
+/// formatting. It uses a RefCell for interior mutability, as we don't want to
+/// require a mutable reference to Config in order to access configuration.
+#[derive(Clone, Default)]
+struct ConfigTracker {
+    set: RefCell<HashSet<&'static str>>,
+}
+
+impl ConfigTracker {
+    fn mark_accessed(&self, name: &'static str) {
+        // We don't ever expect borrowing to fail, as our use of RefCell is very
+        // simple.
+        let mut set = self.set.borrow_mut();
+        set.insert(name);
+    }
+
+    fn was_accessed(&self, name: &'static str) -> bool {
+        self.set.borrow().contains(name)
+    }
+}
+
 macro_rules! create_config {
     ($($i:ident: $ty:ty, $def:expr, $( $dstring:expr ),+ );+ $(;)*) => (
         #[derive(Deserialize, Clone)]
         pub struct Config {
+            #[serde(skip_deserializing)]
+            tracker: ConfigTracker,
+
             $($i: $ty),+
         }
 
@@ -232,6 +258,7 @@ macro_rules! create_config {
 
             $(
             pub fn $i(&self) -> $ty {
+                self.tracker.mark_accessed(stringify!($i));
                 self.$i.clone()
             }
             )+
@@ -324,6 +351,7 @@ macro_rules! create_config {
         impl Default for Config {
             fn default() -> Config {
                 Config {
+                    tracker: ConfigTracker::default(),
                     $(
                         $i: $def,
                     )+