[Issue 22651] undefined reference to ModuleInfo when using imported

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22651

duser at neet.fi changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
          Component|phobos                      |dmd
           Hardware|x86_64                      |All
           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=17181
                 OS|Linux                       |All

--- Comment #2 from duser at neet.fi ---
smaller reproducer:

/// common.d
template myimported() { import myctor; }
/// myctor.d
shared static this(){}
/// empty.d
import common;
/// main.d
import common;
alias x = myimported!();
import empty;
void main(){}

compile: "dmd main.d common.d myctor.d", gives an undefined symbol error for
_D5empty12__ModuleInfoZ

i'm not 1000% familiar with this stuff but i think what happens in the original
example is

1. using imported!"", a module is imported that has a module constructor - this
causes the "needmoduleinfo" flag to be set for a bunch of modules including
"object" (it's not normally set for object)
2. a module is imported that doesn't have a ModuleInfo symbol and isn't
included in compilation - it inherits the needmoduleinfo flag from object
(which it implicitly imports) and linking fails because there's no ModuleInfo
symbol for it

the thing the patch does to fix this is copied from here:
https://github.com/dlang/dmd/blob/375ed51/src/dmd/dsymbolsem.d#L1283-L1292 - it
causes "needmoduleinfo" to be set for the module that uses imported!"" instead
of the module that defines it

the link error in the original example is for std.internal.memory which indeed
doesn't have a ModuleInfo symbol inside libphobos2.so

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