Improve error messages.

Improve error messages and recovery.

R=danrubel@google.com

Committed: https://github.com/dart-lang/sdk/commit/4e8203f9cdf7f1bd697fc5b4692ec17f4679f0a5

[ahe, 2017-06-08 20:55:13]

Description was changed from

==========
Report nice parser error messages.
==========

to

==========
Improve error messages.
==========

[ahe, 2017-06-08 21:02:25]

ahe@google.com changed reviewers:
+ danrubel@google.com

[ahe, 2017-06-08 21:02:25]

Before:

t.dart:1:8: Error: [@7: Non-optional parameters can't have a default value.
Try removing the default value or making the parameter optional.]
main(x = []) {
       ^
After:

t.dart:1:8: Error: Non-optional parameters can't have a default value.
main(x = []) {
       ^

Before:

t.dart:2:1: Warning: No type for: 't'.
import 'b.dart';
^

After:

t.dart:2:1: Warning: 't' is imported from both 'file:///.../a.dart' and
'file:///.../b.dart'.
import 'b.dart';
^

[danrubel, 2017-06-08 21:22:32]

LGTM

[ahe, 2017-06-09 08:13:14]

Dan, I had an error in my local test script, and after fixing that, I found some
additional problems. Could you take another look?

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/lib/src/f...
File pkg/front_end/lib/src/fasta/kernel/kernel_target.dart (right):

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/lib/src/f...
pkg/front_end/lib/src/fasta/kernel/kernel_target.dart:289:
runBuildTransformations();
The parser reports a recoverable error on code like this:

class C {
  foo() async;
}

Fasta treats this as an abstract method and doesn't discard the async modifier.
The async transformer isn't prepared for that, so it crashes when it tries to
visit the null function body of C.foo above.

Before we would throw an InputError and never get as far as running
transformations.

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/lib/src/f...
File pkg/front_end/lib/src/fasta/source/stack_listener.dart (right):

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/lib/src/f...
pkg/front_end/lib/src/fasta/source/stack_listener.dart:255:
addCompileTimeErrorFromMessage(message);
Note: this change also improves recovery from parser errors.

Before this change, these errors would be added to Listener.recoverableErrors
and then checkEmpty would throw an InputError after parsing an element.

Now the error is instead collected by the current library.

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/test/fast...
File pkg/front_end/test/fasta/kompile.status (right):

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/test/fast...
pkg/front_end/test/fasta/kompile.status:33: function_type_recovery: Crash
Now that we don't throw an InputError we get further, and the AstBuilder
crashes.

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/test/fast...
File pkg/front_end/test/fasta/outline.status (left):

https://codereview.chromium.org/2924363002/diff/20001/pkg/front_end/test/fast...
pkg/front_end/test/fasta/outline.status:5: function_type_recovery: Fail # Fixed
in ahe's dev branch.
This is an example of how we recover from an error, and get further and
successfully generate the correct outline.

[ahe, 2017-06-09 08:13:50]

Description was changed from

==========
Improve error messages.
==========

to

==========
Improve error messages and recovery.
==========

[danrubel, 2017-06-09 15:48:04]

LGTM

[ahe, 2017-06-10 08:43:09]

Description was changed from

==========
Improve error messages and recovery.
==========

to

==========
Improve error messages and recovery.

R=danrubel@google.com

Committed:
https://github.com/dart-lang/sdk/commit/4e8203f9cdf7f1bd697fc5b4692ec17f4679f0a5
==========

[ahe, 2017-06-10 08:43:11]

Committed patchset #2 (id:20001) manually as
4e8203f9cdf7f1bd697fc5b4692ec17f4679f0a5 (presubmit successful).