[Issue 9148] 'pure' is broken

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=9148

--- Comment #11 from Kenji Hara <k.hara.pg at gmail.com> ---
I'm adjusting the implicit pure annotation behavior for nested functions in:
https://github.com/D-Programming-Language/dmd/pull/4344

If the nested function is a template, attribute inference is preferred and pure
will be added only when the function is accessing enclosing pure function
context.

auto foo() pure {
    int x;
    auto bar()() {   // template function bar can be impure by default
        // bar will be forced to get weak purity, only when it's trying
        // to access enclosing pure function context.
        //x = 1;

        // otherwise, bar can call impure functions and then
        // it will be inferred to impure.
        impureFuncCall().
    }
}

Once nested template function is inferred to impure, it cannot access enclosing
pure context anymore.

auto foo() pure {
    int x;
    auto bar()() {
        impureFuncCall().
        x = 1;  // Error: impure function 'bar' cannot access variable 'x'
                // declared in enclosing pure function 'foo'
    }
}

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