__traits(compiles, ...) with syntax errors

[Steven Schveighoffer]

On 1/15/19 3:26 AM, Kagamin wrote:
> On Monday, 14 January 2019 at 21:47:40 UTC, Steven Schveighoffer wrote:
>> How many times have you written something like:
>>
>> void foo(T)(T t) if (__traits(compiles, t.bar())) // or 
>> is(typeof(t.bar()))
>> {
>>    t.bar();
>> }
>>
>> And somehow, somewhere, this isn't called? Then you remove the 
>> constraint, and find that there's a syntax error in the bar template 
>> function (like a missing semicolon).
> 
> struct A
> {
>      int f()()
>      {
>          return 0
>      }
> }
> 
> Like this? There's no way for it to ever compile.

Indeed, I realized after posting [1] that it's really stupid typos that 
I make that are still valid syntax, but obviously unintentional. By that 
I mean, it will never compile.

Like:

void foo(T)(T t)
{
    int x = 1;
    t.fun(X);
}

What I was trying to say is that I wanted a way to separate "obvious" 
errors from errors that happen because of the template parameters. But I 
think there simply isn't a way to do it. The best we can do might be to 
try and force specific instantiations to see why they don't compile.

-Steve

[1] https://forum.dlang.org/post/q1jequ$r63$1@digitalmars.com