fix #29108, improve inference error messages

fix #29108, improve inference error messages

R=leafp@google.com

Committed: https://github.com/dart-lang/sdk/commit/4f9fff9ebd6f22051e438f33b3585e25bb91ccd5

[Jennifer Messerly, 2017-03-20 22:03:27]

jmesserly@google.com changed reviewers:
+ leafp@google.com

[Jennifer Messerly, 2017-03-20 22:03:27]

thoughts on these improvements?

There's 3 primary ones:
* extends clause omitted unless it failed
* display expected/actual types so they line up
* add a different message for function type instantiations

... also some refactoring to hopefully make the code more clear.

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
File pkg/analyzer/test/generated/strong_mode_test.dart (right):

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1123: must be a   '(T) → T'.
should we show this as (double) → double?

... it's interesting we'd do this with argument types but not return type.
Maybe it's the wording? Or does it make sense because the direction is
different?

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1204: Type parameter 'T'
declared to extend 'num'.
like I feel this one is pretty good, but YMMV

[Leaf, 2017-03-20 22:46:55]

lgtm

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
File pkg/analyzer/test/generated/strong_mode_test.dart (right):

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1121: Tried to infer 'double'
for 'T' but it did not work:
<bikeshed>
"it did not work" feels a bit clunky to me.  What do you think of "which doesn't
work" instead?
</bikeshed>

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1122: Argument 'f' inferred as
'(int) → double'
The key to this section is making it absolutely 100% crystal clear that the
first type is the type of the actual argument, and the second type is the
declared type of the parameter.  What do you think of 

Parameter 'f' declared as `(T) -> T`
Argument has type '(int) -> double'

?

This is also consistent with the order and phrasing that you use for other kinds
of constraints below (`Return type declared as...`, `Function type declared
as...`).

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1204: Type parameter 'T'
declared to extend 'num'.
On 2017/03/20 22:03:27, Jennifer Messerly wrote:
> like I feel this one is pretty good, but YMMV

Agreed.

[Jennifer Messerly, 2017-03-21 01:08:08]

Thanks Leaf!!!

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
File pkg/analyzer/test/generated/strong_mode_test.dart (right):

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1121: Tried to infer 'double'
for 'T' but it did not work:
On 2017/03/20 22:46:55, Leaf wrote:
> <bikeshed>
> "it did not work" feels a bit clunky to me.  What do you think of "which
doesn't
> work" instead?
> </bikeshed>

Done.

[Jennifer Messerly, 2017-03-21 01:08:36]

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
File pkg/analyzer/test/generated/strong_mode_test.dart (right):

https://codereview.chromium.org/2757233004/diff/1/pkg/analyzer/test/generated...
pkg/analyzer/test/generated/strong_mode_test.dart:1122: Argument 'f' inferred as
'(int) → double'
On 2017/03/20 22:46:55, Leaf wrote:
> The key to this section is making it absolutely 100% crystal clear that the
> first type is the type of the actual argument, and the second type is the
> declared type of the parameter.  What do you think of 
> 
> Parameter 'f' declared as `(T) -> T`
> Argument has type '(int) -> double'
> 
> ?
> 
> This is also consistent with the order and phrasing that you use for other
kinds
> of constraints below (`Return type declared as...`, `Function type declared
> as...`).

oops! also I did this one too. Forgot to save comment :)

[Jennifer Messerly, 2017-03-21 01:12:59]

Description was changed from

==========
fix #29108, improve inference error messages
==========

to

==========
fix #29108, improve inference error messages

R=leafp@google.com

Committed:
https://github.com/dart-lang/sdk/commit/4f9fff9ebd6f22051e438f33b3585e25bb91ccd5
==========

[Jennifer Messerly, 2017-03-21 01:13:01]

Committed patchset #3 (id:40001) manually as
4f9fff9ebd6f22051e438f33b3585e25bb91ccd5 (presubmit successful).