From a1e240ccec087c64d0adf27d9c4cc96ab104d551 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 27 May 2016 21:45:15 +0200
Subject: [PATCH 1/4] Improve E0137 error explanatIon

---
 src/librustc/diagnostics.rs | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index c64f0ddac50d0..56d57d39be6e2 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -392,9 +392,30 @@ function `main()`. If there are multiple such functions, please rename one.
 "##,
 
 E0137: r##"
+More than one function was declared with the `#[main]` attribute.
+
+Erroneous code example:
+
+```compile_fail
+#![feature(main)]
+
+#[main]
+fn foo() {}
+
+#[main]
+fn f() {} // error: multiple functions with a #[main] attribute
+```
+
 This error indicates that the compiler found multiple functions with the
 `#[main]` attribute. This is an error because there must be a unique entry
-point into a Rust program.
+point into a Rust program. Example:
+
+```
+#![feature(main)]
+
+#[main]
+fn f() {} // ok!
+```
 "##,
 
 E0138: r##"

From 360d7234c7ce1392c2730fba2e7d9b33f3ff9e5f Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 27 May 2016 21:47:59 +0200
Subject: [PATCH 2/4] Improve E0138 error explanation

---
 src/librustc/diagnostics.rs | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index 56d57d39be6e2..7c350987aa1e8 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -419,9 +419,32 @@ fn f() {} // ok!
 "##,
 
 E0138: r##"
+More than one function was declared with the `#[start]` attribute.
+
+Erroneous code example:
+
+```compile_fail
+#![feature(start)]
+
+#[start]
+fn foo(argc: isize, argv: *const *const u8) -> isize {}
+
+#[start]
+fn f(argc: isize, argv: *const *const u8) -> isize {}
+// error: multiple 'start' functions
+```
+
 This error indicates that the compiler found multiple functions with the
 `#[start]` attribute. This is an error because there must be a unique entry
-point into a Rust program.
+point into a Rust program. Example:
+
+
+```
+#![feature(start)]
+
+#[start]
+fn foo(argc: isize, argv: *const *const u8) -> isize {} // ok!
+```
 "##,
 
 // FIXME link this to the relevant turpl chapters for instilling fear of the

From 4fa84830f8a91a2a8db988afec96b416ae2654c0 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 27 May 2016 21:57:06 +0200
Subject: [PATCH 3/4] improve E0152 error explanation

---
 src/librustc/diagnostics.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index 7c350987aa1e8..a410a5949bdc8 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -525,6 +525,17 @@ call to `mem::forget(v)` in case you want to avoid destructors being called.
 "##,
 
 E0152: r##"
+A lang item was redefined.
+
+Erroneous code example:
+
+```compile_fail
+#![feature(lang_items)]
+
+#[lang = "panic_fmt"]
+struct Foo; // error: duplicate lang item found: `panic_fmt`
+```
+
 Lang items are already implemented in the standard library. Unless you are
 writing a free-standing application (e.g. a kernel), you do not need to provide
 them yourself.

From 31b9060ede89c7c11d7d829c3d4b50649bb7f07e Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 27 May 2016 22:05:10 +0200
Subject: [PATCH 4/4] Improve E0161 error explanation

---
 src/librustc/diagnostics.rs        |  3 +--
 src/librustc_passes/diagnostics.rs | 27 ++++++++++++++++++++++++++-
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index a410a5949bdc8..d838de4a33122 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -438,12 +438,11 @@ This error indicates that the compiler found multiple functions with the
 `#[start]` attribute. This is an error because there must be a unique entry
 point into a Rust program. Example:
 
-
 ```
 #![feature(start)]
 
 #[start]
-fn foo(argc: isize, argv: *const *const u8) -> isize {} // ok!
+fn foo(argc: isize, argv: *const *const u8) -> isize { 0 } // ok!
 ```
 "##,
 
diff --git a/src/librustc_passes/diagnostics.rs b/src/librustc_passes/diagnostics.rs
index 77f896e011b93..cba8bd73c014e 100644
--- a/src/librustc_passes/diagnostics.rs
+++ b/src/librustc_passes/diagnostics.rs
@@ -50,11 +50,36 @@ match 5u32 {
 "##,
 
 E0161: r##"
+A value was moved. However, its size was not known at compile time, and only
+values of a known size can be moved.
+
+Erroneous code example:
+
+```compile_fail
+#![feature(box_syntax)]
+
+fn main() {
+    let array: &[isize] = &[1, 2, 3];
+    let _x: Box<[isize]> = box *array;
+    // error: cannot move a value of type [isize]: the size of [isize] cannot
+    //        be statically determined
+}
+```
+
 In Rust, you can only move a value when its size is known at compile time.
 
 To work around this restriction, consider "hiding" the value behind a reference:
 either `&x` or `&mut x`. Since a reference has a fixed size, this lets you move
-it around as usual.
+it around as usual. Example:
+
+```
+#![feature(box_syntax)]
+
+fn main() {
+    let array: &[isize] = &[1, 2, 3];
+    let _x: Box<&[isize]> = box array; // ok!
+}
+```
 "##,
 
 E0265: r##"