Validate the formatting of extended errors.

src/librustc/diagnostics.rs

@@ -55,15 +55,17 @@ underscore `_` wildcard pattern can be added after all other patterns to match
 
 // FIXME: Remove duplication here?
 E0005: r##"
-Patterns used to bind names must be irrefutable, that is, they must guarantee that a
-name will be extracted in all cases. If you encounter this error you probably need
-to use a `match` or `if let` to deal with the possibility of failure.
+Patterns used to bind names must be irrefutable, that is, they must guarantee
+that a name will be extracted in all cases. If you encounter this error you
+probably need to use a `match` or `if let` to deal with the possibility of
+failure.
 "##,
 
 E0006: r##"
-Patterns used to bind names must be irrefutable, that is, they must guarantee that a
-name will be extracted in all cases. If you encounter this error you probably need
-to use a `match` or `if let` to deal with the possibility of failure.
+Patterns used to bind names must be irrefutable, that is, they must guarantee
+that a name will be extracted in all cases. If you encounter this error you
+probably need to use a `match` or `if let` to deal with the possibility of
+failure.
 "##,
 
 E0007: r##"
@@ -217,6 +219,26 @@ use Method::*;
 enum Method { GET, POST }
 "##,
 
+E0267: r##"
+This error indicates the use of loop keyword (break or continue) inside a
+closure but outside of any loop. Break and continue can be used as normal
+inside closures as long as they are also contained within a loop. To halt the
+execution of a closure you should instead use a return statement.
+"##,
+
+E0268: r##"
+This error indicates the use of loop keyword (break or continue) outside of a
+loop. Without a loop to break out of or continue in, no sensible action can be
+taken.
+"##,
+
+E0296: r##"
+This error indicates that the given recursion limit could not be parsed. Ensure
+that the value provided is a positive integer between quotes, like so:
+
+#![recursion_limit="1000"]
+"##,
+
 E0297: r##"
 Patterns used to bind names must be irrefutable. That is, they must guarantee
 that a name will be extracted in all cases. Instead of pattern matching the
@@ -277,21 +299,23 @@ In certain cases it is possible for sub-bindings to violate memory safety.
 Updates to the borrow checker in a future version of Rust may remove this
 restriction, but for now patterns must be rewritten without sub-bindings.
 
-// Code like this...
-match Some(5) {
-    ref op_num @ Some(num) => ...
+// Before.
+match Some("hi".to_string()) {
+    ref op_string_ref @ Some(ref s) => ...
     None => ...
 }
 
-// ... should be updated to code like this.
-match Some(5) {
-    Some(num) => {
-        let op_num = &Some(num);
+// After.
+match Some("hi".to_string()) {
+    Some(ref s) => {
+        let op_string_ref = &Some(&s);
         ...
     }
     None => ...
 }
 
+The `op_string_ref` binding has type &Option<&String> in both cases.
+
 See also https://github.com/rust-lang/rust/issues/14587
 "##,
 
@@ -338,8 +362,6 @@ register_diagnostics! {
     E0264, // unknown external lang item
     E0265, // recursive constant
     E0266, // expected item
-    E0267, // thing inside of a closure
-    E0268, // thing outside of a loop
     E0269, // not all control paths return a value
     E0270, // computation may converge in a function marked as diverging
     E0271, // type mismatch resolving
@@ -357,7 +379,6 @@ register_diagnostics! {
     E0283, // cannot resolve type
     E0284, // cannot resolve type
     E0285, // overflow evaluation builtin bounds
-    E0296, // malformed recursion limit attribute
     E0298, // mismatched types between arms
     E0299, // mismatched types between arms
     E0300, // unexpanded macro

src/libsyntax/diagnostics/plugin.rs

@@ -20,6 +20,9 @@ use parse::token;
 use ptr::P;
 use util::small_vector::SmallVector;
 
+// Maximum width of any line in an extended error description (inclusive).
+const MAX_DESCRIPTION_WIDTH: usize = 80;
+
 thread_local! {
     static REGISTERED_DIAGNOSTICS: RefCell<BTreeMap<Name, Option<Name>>> = {
         RefCell::new(BTreeMap::new())
@@ -92,6 +95,24 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
         }
         _ => unreachable!()
     };
+    // Check that the description starts and ends with a newline and doesn't
+    // overflow the maximum line width.
+    description.map(|raw_msg| {
+        let msg = raw_msg.as_str();
+        if !msg.starts_with("\n") || !msg.ends_with("\n") {
+            ecx.span_err(span, &format!(
+                "description for error code {} doesn't start and end with a newline",
+                token::get_ident(*code)
+            ));
+        }
+        if msg.lines().any(|line| line.len() > MAX_DESCRIPTION_WIDTH) {
+            ecx.span_err(span, &format!(
+                "description for error code {} contains a line longer than {} characters",
+                token::get_ident(*code), MAX_DESCRIPTION_WIDTH
+            ));
+        }
+        raw_msg
+    });
     with_registered_diagnostics(|diagnostics| {
         if diagnostics.insert(code.name, description).is_some() {
             ecx.span_err(span, &format!(