[Issue 21844] New: makedeps option adds spurious/incorrect dependency

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21844

          Issue ID: 21844
           Summary: makedeps option adds spurious/incorrect dependency
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: minor
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ichneumwn at gmail.com

Using ldc2 (1.25.0 (DMD v2.095.1, LLVM 10.0.0)  or dmd  (DMD64 D Compiler
v2.095.0), compiling the following test code:

test.d:
import std.experimental.logger : info;
void main() {
    info("hello");
}

using: dmd -makedeps=deps.txt test.d

generates:
  test.d \
  /usr/include/dmd/phobos/std/experimental/logger/package.d \
  /usr/include/dmd/druntime/import/object.d \
  /usr/include/dmd/druntime/import/core/attribute.d \
...
  /usr/include/dmd/druntime/import/core/stdc/fenv.d \
  test_loggerconfig.d \
  /usr/include/dmd/druntime/import/core/sys/linux/time.d

Note the test_loggerconfig.d. This dependency is only generated if info() is
used somewhere in the code, i.e. it is not triggered if the body of main is
empty in the example above.

info() is an alias leading to the template defaultLogFunction in
std.experimental.logger.core.d

This is an excerpt from the logger.core.d code:
template moduleLogLevel(string moduleName)
if (moduleName.length)
{
    import std.string : format;
    mixin(q{
        static if (__traits(compiles, {import %1$s : logLevel;}))
        {
            import %1$s : logLevel;

I guess the import-in-mixin might be throwing off the makedeps logic?

This implicit non-existing dependency causes meson/ninja to recompile each time
it is invoked

Cheers!

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