Inferred attributes errors in template function.

[Tejas]

On Friday, 27 May 2022 at 08:39:08 UTC, vit wrote:
> Hello, I have this problem:
>
> ```d
> static int i;
>
> void bar(T)(){
> 	static if(is(T == int))
>         (()@system => 1)();
>     static if(is(T == float))
>         i = 42;
>
> }
> void foo(T)(){
> 	bar!T();
> }
>
> void main()@safe pure{
> 	foo!long();
> 	foo!float();	//Error: `pure` function `D main` cannot call 
> impure function `onlineapp.foo!float.foo`
> 	foo!int();		//Error: `@safe` function `D main` cannot call 
> `@system` function `onlineapp.foo!int.foo`
> }
> ```
>
> When template function foo is called and its inferred 
> attributes are not compatible with attributes of main, errors 
> are not really useful. Compiler print that foo!float is not 
> pure or foo!int is not @safe but doesn't tell why. Is in dmd 
> some flag that print errors similarly to this?:
>
> ```d
> void main()@safe pure{
> 	foo!long();
> 	foo!float();	
>     	//Error: `pure` function `D main` cannot call impure 
> function `onlineapp.foo!float.foo`
>     	//Error: potentially `pure` function 
> `onlineapp.foo!float.foo` cannot call impure function 
> `onlineapp.bar!float.bar`
>     	//Error: potentially `pure` function 
> `onlineapp.bar!float.bar` cannot access mutable static data `i`
> 	foo!int();		
>     	//Error: `@safe` function `D main` cannot call `@system` 
> function `onlineapp.foo!int.foo`
>     	//Error: potentially `@safe` function 
> `onlineapp.foo!int.foo` cannot call `@system` function 
> `onlineapp.bar!int.bar`
>      	//Error: potentially `@safe` function 
> `onlineapp.bar!int.bar` cannot call `@system` delegate 
> `onlineapp.bar!int.bar.__lambda1`
> }
> ```

Use `-verrors=context` for dmd

```d
static int i;

void bar(T)(){
	static if(is(T == int))
         (()@system => 1)();
     static if(is(T == float))
         i = 42;

}
void foo(T)(){
	bar!T();
}

void main()@safe pure{
	foo!long();
	foo!float();	/+ onlineapp.d(16): Error: `pure` function `D main` 
cannot call impure function `onlineapp.foo!float.foo`
	foo!float();	
           ^		+/

	foo!int();		/+onlineapp.d(18): Error: `@safe` function `D main` 
cannot call `@system` function `onlineapp.foo!int.foo`
	foo!int();		
         ^		+/
}
```