In symbol lookup, with statement becomes stronger than an inner scope import statement

[dlangBugzillaToGithub]

karita (@ShigekiKarita) reported this on 2018-10-13T04:48:24Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19305

CC List

• RazvanN
• Stefan Koch

Description

I found a breaking change of symbol  from DMD2.073.0. I think this change comes from a conflict between statement spec 4.3.2 and module spec 11.19.1.

see 4.3.2 in https://docarchives.dlang.io/v2.081.0/spec/module.html
see 11.19.1 in https://docarchives.dlang.io/v2.081.0/spec/statement.html#with-statement


running example 
https://wandbox.org/permlink/5bDsMZeqKYh4runs
-------

module a;

enum f = "a";


module b;

enum f = "b";


module main;

import std.stdio;
import a;
import b;


void main() {
    with (a) {
        // 11.19.1 Within the with body the referenced object is searched first for identifier symbols
        assert(f == "a");
        // 4.3.2 When a symbol name is used unqualified, a two-phase lookup will happen. 
        // First, the module scope will be searched, starting from the innermost scope. ...
        // Symbol lookup stops as soon as a symbol is found. 
        // If two symbols with the same name are found at the same lookup phase,
        //  this ambiguity will result in a compilation error.
        import b;
        static if (__VERSION__ >= 2073) {
            assert(f == "a");
        } else {
            assert(f == "b");                    
        }
    }
}

[dlangBugzillaToGithub]

razvan.nitu1305 commented on 2018-11-27T12:50:07Z

I don't see what the problem is. master git HEAD compiles this successfully as it should. The with scope takes precedence over imports. The rules are clear. Maybe older versions had a bug in it which was solved.

Closing as invalid. Please reopen if I am missing something.

[dlangBugzillaToGithub]

uplink.coder commented on 2018-11-27T14:57:39Z

I think this example should cause an ambiguity error.

Or the spec should be amended to explicitly break this tie.

[dlangBugzillaToGithub]

shigekikarita commented on 2018-11-27T15:13:03Z

Yes, the current spec defines both with statement and innermost scope are "first". It should be ambiguous.

[dlangBugzillaToGithub]

shigekikarita commented on 2018-11-27T15:22:02Z

For more clear example, 2.083 runs this without any errors.

void main() {
    with (a) {
        {
            import b;
            assert(f == "a");
        }
    }
}