[Issue 13967] New: More precise non- at nogc error messages

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13967

          Issue ID: 13967
           Summary: More precise non- at nogc error messages
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Keywords: diagnostic
          Severity: enhancement
          Priority: P1
         Component: DMD
          Assignee: nobody at puremagic.com
          Reporter: bearophile_hugs at eml.cc

>From the first error message it seems "joiner" is @nogc, but the second error
message shows that it's the iteration of r1 (calling its .front) non- at nogc:


void main() {
    import std.range: iota;
    import std.algorithm: map, joiner;
    static foo(in uint n) @nogc {
        auto r1 = n.iota.map!(x => x.iota.map!(y => x));
        auto r2 = r1.joiner;
        foreach (z; r1) {}
    }
}


test.d(6,21): Error: @nogc function 'test.main.foo' cannot call non- at nogc
function 'std.algorithm.joiner!(MapResult!(__lambda2, Result)).joiner'
test.d(7,9): Error: @nogc function 'test.main.foo' cannot call non- at nogc
function 'test.main.foo.MapResult!(__lambda2, Result).MapResult.front'


I'd like error messages to better pinpoint where the non- at nogc actually is.
Because with library functions like "joiner" you know they are designed to be
@nogc, but with user-written ranges it's harder to find where the problem is.

See also Issue 12829

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