From 84ef603c8400db203fefd714de963c88e5523424 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Thu, 17 Sep 2020 21:11:22 +0200
Subject: [PATCH 1/2] Fix 'FIXME' about using NonZeroU32 instead of u32.

It was blocked by #58732 (const fn NonZeroU32::new), which is fixed now.
---
 compiler/rustc_feature/src/accepted.rs |  4 ++--
 compiler/rustc_feature/src/active.rs   |  4 ++--
 compiler/rustc_feature/src/lib.rs      | 21 +++++++++++----------
 compiler/rustc_feature/src/removed.rs  |  6 +++---
 4 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 0477f6f149b87..e2492efb9d79e 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -1,6 +1,6 @@
 //! List of the accepted feature gates.
 
-use super::{Feature, State};
+use super::{to_nonzero, Feature, State};
 use rustc_span::symbol::sym;
 
 macro_rules! declare_features {
@@ -14,7 +14,7 @@ macro_rules! declare_features {
                     state: State::Accepted,
                     name: sym::$feature,
                     since: $ver,
-                    issue: $issue,
+                    issue: to_nonzero($issue),
                     edition: None,
                     description: concat!($($doc,)*),
                 }
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index d4664292a0cbd..7dcd563228f7f 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -1,6 +1,6 @@
 //! List of the active feature gates.
 
-use super::{Feature, State};
+use super::{to_nonzero, Feature, State};
 
 use rustc_span::edition::Edition;
 use rustc_span::symbol::{sym, Symbol};
@@ -29,7 +29,7 @@ macro_rules! declare_features {
                     state: State::Active { set: set!($feature) },
                     name: sym::$feature,
                     since: $ver,
-                    issue: $issue,
+                    issue: to_nonzero($issue),
                     edition: $edition,
                     description: concat!($($doc,)*),
                 }
diff --git a/compiler/rustc_feature/src/lib.rs b/compiler/rustc_feature/src/lib.rs
index 15564a59658cb..c70f3c3cd402f 100644
--- a/compiler/rustc_feature/src/lib.rs
+++ b/compiler/rustc_feature/src/lib.rs
@@ -46,17 +46,11 @@ pub struct Feature {
     pub state: State,
     pub name: Symbol,
     pub since: &'static str,
-    issue: Option<u32>, // FIXME: once #58732 is done make this an Option<NonZeroU32>
+    issue: Option<NonZeroU32>,
     pub edition: Option<Edition>,
     description: &'static str,
 }
 
-impl Feature {
-    fn issue(&self) -> Option<NonZeroU32> {
-        self.issue.and_then(NonZeroU32::new)
-    }
-}
-
 #[derive(Copy, Clone, Debug)]
 pub enum Stability {
     Unstable,
@@ -102,8 +96,8 @@ impl UnstableFeatures {
 fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
     if let Some(info) = ACTIVE_FEATURES.iter().find(|t| t.name == feature) {
         // FIXME (#28244): enforce that active features have issue numbers
-        // assert!(info.issue().is_some())
-        info.issue()
+        // assert!(info.issue.is_some())
+        info.issue
     } else {
         // search in Accepted, Removed, or Stable Removed features
         let found = ACCEPTED_FEATURES
@@ -112,12 +106,19 @@ fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
             .chain(STABLE_REMOVED_FEATURES)
             .find(|t| t.name == feature);
         match found {
-            Some(found) => found.issue(),
+            Some(found) => found.issue,
             None => panic!("feature `{}` is not declared anywhere", feature),
         }
     }
 }
 
+const fn to_nonzero(n: Option<u32>) -> Option<NonZeroU32> {
+    match n {
+        None => None,
+        Some(n) => NonZeroU32::new(n),
+    }
+}
+
 pub enum GateIssue {
     Language,
     Library(Option<NonZeroU32>),
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index 8d410894e8b19..a480ddc7f34b1 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -1,6 +1,6 @@
 //! List of the removed feature gates.
 
-use super::{Feature, State};
+use super::{to_nonzero, Feature, State};
 use rustc_span::symbol::sym;
 
 macro_rules! declare_features {
@@ -14,7 +14,7 @@ macro_rules! declare_features {
                     state: State::Removed { reason: $reason },
                     name: sym::$feature,
                     since: $ver,
-                    issue: $issue,
+                    issue: to_nonzero($issue),
                     edition: None,
                     description: concat!($($doc,)*),
                 }
@@ -32,7 +32,7 @@ macro_rules! declare_features {
                     state: State::Stabilized { reason: None },
                     name: sym::$feature,
                     since: $ver,
-                    issue: $issue,
+                    issue: to_nonzero($issue),
                     edition: None,
                     description: concat!($($doc,)*),
                 }

From 2140d80a9d69cce7a9fb2c90051af4328737a446 Mon Sep 17 00:00:00 2001
From: Mara Bos <m-ou.se@m-ou.se>
Date: Thu, 1 Oct 2020 17:32:23 +0200
Subject: [PATCH 2/2] Add note about possible future improvement

Co-authored-by: David Tolnay <dtolnay@gmail.com>
---
 compiler/rustc_feature/src/lib.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler/rustc_feature/src/lib.rs b/compiler/rustc_feature/src/lib.rs
index c70f3c3cd402f..68ac2841fed70 100644
--- a/compiler/rustc_feature/src/lib.rs
+++ b/compiler/rustc_feature/src/lib.rs
@@ -113,6 +113,8 @@ fn find_lang_feature_issue(feature: Symbol) -> Option<NonZeroU32> {
 }
 
 const fn to_nonzero(n: Option<u32>) -> Option<NonZeroU32> {
+    // Can be replaced with `n.and_then(NonZeroU32::new)` if that is ever usable
+    // in const context. Requires https://github.com/rust-lang/rfcs/pull/2632.
     match n {
         None => None,
         Some(n) => NonZeroU32::new(n),