Change a few error messages to give code suggestions

PR #24242 added the ability to the compiler to directly give suggestions about
how to modify code to fix an error. The new errors look like this:

    foobar.rs:5:12: 5:25 error: expected a path on the left-hand side of `+`,
                                not `&'static Copy` [E0178]
    foobar.rs:5     let x: &'static Copy + 'static;
                           ^~~~~~~~~~~~~
    foobar.rs:5:12: 5:35 help: try adding parentheses (per RFC 438):
    foobar.rs:      let x: &'static (Copy + 'static);

    foobar.rs:2:13: 2:23 error: cast to unsized type: `&_` as `core::marker::Copy`
    foobar.rs:2     let x = &1 as Copy;
                            ^~~~~~~~~~
    foobar.rs:2:19: 2:23 help: try casting to a reference instead:
    foobar.rs:      let x = &1 as &Copy;

    foobar.rs:7:24: 7:25 error: expected expression, found `;`
    foobar.rs:7     let x = box (1 + 1);
                                       ^
    foobar.rs:7:13: 7:16 help: try using `box()` instead:
    foobar.rs:      let x = box() (1 + 1);

This also modifies compiletest to give the ability to directly test suggestions
given by error messages.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/compiletest/runtest.rs b/src/compiletest/runtest.rs
index 8ae36393182..91550ae7461 100644
--- a/src/compiletest/runtest.rs
+++ b/src/compiletest/runtest.rs
@@ -979,6 +979,7 @@ fn check_expected_errors(expected_errors: Vec<errors::ExpectedError> ,
     // is the ending point, and * represents ANSI color codes.
     for line in proc_res.stderr.lines() {
         let mut was_expected = false;
+        let mut prev = 0;
         for (i, ee) in expected_errors.iter().enumerate() {
             if !found_flags[i] {
                 debug!("prefix={} ee.kind={} ee.msg={} line={}",
@@ -986,6 +987,17 @@ fn check_expected_errors(expected_errors: Vec<errors::ExpectedError> ,
                        ee.kind,
                        ee.msg,
                        line);
+                // Suggestions have no line number in their output, so take on the line number of
+                // the previous expected error
+                if ee.kind == "suggestion" {
+                    assert!(expected_errors[prev].kind == "help",
+                            "SUGGESTIONs must be preceded by a HELP");
+                    if line.contains(&ee.msg) {
+                        found_flags[i] = true;
+                        was_expected = true;
+                        break;
+                    }
+                }
                 if (prefix_matches(line, &prefixes[i]) || continuation(line)) &&
                     line.contains(&ee.kind) &&
                     line.contains(&ee.msg) {
@@ -994,6 +1006,7 @@ fn check_expected_errors(expected_errors: Vec<errors::ExpectedError> ,
                     break;
                 }
             }
+            prev = i;
         }
 
         // ignore this msg which gets printed at the end