From 46bfc48272ba5312c439557e2901e1a4778e9487 Mon Sep 17 00:00:00 2001
From: pankajchaudhary5 <pankajchaudhary172@gmail.com>
Date: Sun, 10 May 2020 11:39:51 +0530
Subject: [PATCH] Added proper explanation of ErrorCode-E0687

---
 src/librustc_error_codes/error_codes.rs       |  2 +-
 src/librustc_error_codes/error_codes/E0687.md | 36 +++++++++++++++++++
 src/test/ui/in-band-lifetimes/E0687.stderr    |  1 +
 .../ui/in-band-lifetimes/E0687_where.stderr   |  1 +
 4 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 src/librustc_error_codes/error_codes/E0687.md

diff --git a/src/librustc_error_codes/error_codes.rs b/src/librustc_error_codes/error_codes.rs
index 225ede851b4d9..c54cb81b00dbe 100644
--- a/src/librustc_error_codes/error_codes.rs
+++ b/src/librustc_error_codes/error_codes.rs
@@ -380,6 +380,7 @@ E0668: include_str!("./error_codes/E0668.md"),
 E0669: include_str!("./error_codes/E0669.md"),
 E0670: include_str!("./error_codes/E0670.md"),
 E0671: include_str!("./error_codes/E0671.md"),
+E0687: include_str!("./error_codes/E0687.md"),
 E0689: include_str!("./error_codes/E0689.md"),
 E0690: include_str!("./error_codes/E0690.md"),
 E0691: include_str!("./error_codes/E0691.md"),
@@ -599,7 +600,6 @@ E0751: include_str!("./error_codes/E0751.md"),
     E0640, // infer outlives requirements
 //  E0645, // trait aliases not finished
     E0667, // `impl Trait` in projections
-    E0687, // in-band lifetimes cannot be used in `fn`/`Fn` syntax
     E0688, // in-band lifetimes cannot be mixed with explicit lifetime binders
 //  E0694, // an unknown tool name found in scoped attributes
     E0696, // `continue` pointing to a labeled block
diff --git a/src/librustc_error_codes/error_codes/E0687.md b/src/librustc_error_codes/error_codes/E0687.md
new file mode 100644
index 0000000000000..67b7db2d31fde
--- /dev/null
+++ b/src/librustc_error_codes/error_codes/E0687.md
@@ -0,0 +1,36 @@
+In-band lifetimes cannot be used in `fn`/`Fn` syntax.
+
+Erroneous code examples:
+
+```compile_fail,E0687
+#![feature(in_band_lifetimes)]
+
+fn foo(x: fn(&'a u32)) {} // error!
+
+fn bar(x: &Fn(&'a u32)) {} // error!
+
+fn baz(x: fn(&'a u32), y: &'a u32) {} // error!
+
+struct Foo<'a> { x: &'a u32 }
+
+impl Foo<'a> {
+    fn bar(&self, x: fn(&'a u32)) {} // error!
+}
+```
+
+Lifetimes used in `fn` or `Fn` syntax must be explicitly
+declared using `<...>` binders. For example:
+
+```
+fn foo<'a>(x: fn(&'a u32)) {} // ok!
+
+fn bar<'a>(x: &Fn(&'a u32)) {} // ok!
+
+fn baz<'a>(x: fn(&'a u32), y: &'a u32) {} // ok!
+
+struct Foo<'a> { x: &'a u32 }
+
+impl<'a> Foo<'a> {
+    fn bar(&self, x: fn(&'a u32)) {} // ok!
+}
+```
diff --git a/src/test/ui/in-band-lifetimes/E0687.stderr b/src/test/ui/in-band-lifetimes/E0687.stderr
index e8e5100e00e07..7aea2f220466c 100644
--- a/src/test/ui/in-band-lifetimes/E0687.stderr
+++ b/src/test/ui/in-band-lifetimes/E0687.stderr
@@ -24,3 +24,4 @@ LL |     fn bar(&self, x: fn(&'a u32)) {}
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0687`.
diff --git a/src/test/ui/in-band-lifetimes/E0687_where.stderr b/src/test/ui/in-band-lifetimes/E0687_where.stderr
index b422869c4db89..af0f9665f5d06 100644
--- a/src/test/ui/in-band-lifetimes/E0687_where.stderr
+++ b/src/test/ui/in-band-lifetimes/E0687_where.stderr
@@ -12,3 +12,4 @@ LL | fn baz(x: &impl Fn(&'a u32)) {}
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0687`.