[patch] Improve diagnostic on default-initializing const variables (PR20208)

[Richard Smith]

+/// Prints a fixit for adding a null initializer for |Entity|. Call this
only
+/// right after emitting a diagnostic.
+static void maybeEmitNullInitializationFixit(Sema &S,
+                                             InitializationSequence
&Sequence,
+                                             const InitializedEntity
&Entity) {

s/null/zero/g

Otherwise, LGTM.


On Tue, Jul 22, 2014 at 9:18 AM, Nico Weber <thakis at chromium.org> wrote:

>  Ideas? Easiest would be to put the fixit on a note, but the note would
>>> just repeat the snippet from the diag itself, which isn't great.
>>>
>>
>> We do that in a lot of cases; this wouldn't be so bad, and it'd be safer.
>> The current approach is also workable, because we never make a choice based
>> on whether default initialization of a variable is valid, but it seems
>> fragile.
>>
>> The nice thing about putting it in a separate note is that you can point
>> the caret directly at the place where the fixit text should be inserted,
>> while still having the main diagnostic point at the entity being
>> initialized; that tends to make fixits much more obvious.
>>
>
> Ok, here's a patch that adds the fixit on a note instead. The code change
> is now very simple. The diagnostic looks like this:
>
> test.cc:2:9: error: default initialization of an object of const type
> 'const A' without a user-provided default constructor
> const A aasdf;
>         ^
> test.cc:2:14: note: add an explicit initializer to initialize 'aasdf'
> const A aasdf;
>              ^
>               = {}
> 1 error generated.
>
> Maybe it should be " add an explicit initializer for 'aasdf'"? That's
> shorter, but it sounds too confident maybe.
>
> The test case updates are mostly boring.
> In cxx1y-variable-templates_in_class.cpp, the variable name for a template
> is printed as "…to initialize 'b<int, int>'" with a note "in instantiation
> of". I found that a bit surprising, but it matches the diagnostic on the
> same line, so I suppose that's ok.
>

You could use %q0 in the diagnostic if you want to see 'B4::b<int, int>'
here. (If it's not that, I'm not sure which part you find surprising here.)
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