static analysis: how to test code reachability at compile time

[Diggory]

On Tuesday, 21 May 2013 at 21:15:58 UTC, Timothee Cour wrote:
>  I'd like to have the following tools to help with static 
> analysis & code
> coverage:
>
> 1) test whether code is reachable or not.
>
> Of course it only works for executables and may have some 
> caveats (eg:
> goto), but its still useful diagnostic tool.
>
> __traits(isReachable): true when the current context can be 
> reached via at
> least one code path starting from main():
>
> ----
> void fun1(){
> //__traits(isReachable) would be false here because even though 
> fun1 is
> called by fun2, it can never be called starting from main().
> }
> void fun2(){fun1;}
> void fun3(){} // would also be false, because of static 
> if(temp); with temp
> being known to be 0 at compile time.
> void fun4(){
> return;
> //__traits(isReachable) would be false here because all code 
> paths return
> above this point.
> }
> void main(){enum temp=0; static if(temp) fun3; fun4;}
> ----
>
> When a pointer to a function is taken, we may want to assume by 
> convention
> that __traits(isReachable) is true.
>
> This would enable for example to make sure a given code is 
> never called.
> Note, static assert(0) is not the same.
>
> 2)
> static code call graph: know caller/calling functions for a 
> given function.
>
>
> 3) static code coverage
> this would allow us to tell at compile time the code coverage 
> of a module;
> it is larger than runtime coverage, but still useful to find 
> dead code.

It would be very easy to introduce paradoxes if this were 
possible, simply use a static if to call something only if it is 
unreachable.