Bug 19884 – [regression] Error: alias op = op; cannot alias itself, use a qualified name to create an overload set

This regression is so strange that I'm not sure what's the best title for the bug beyond the compiler's strange error message. Reduced code: ------ mixin template genCtEvaluate() { void evaluate(alias op)() { } } struct S { mixin genCtEvaluate!() mixinEval; alias evaluate = mixinEval.evaluate; void evaluate() { } } alias List(Ops...) = Ops; void main() { S g; foreach (op; List!(0)) { g.evaluate!op(); } } ------ Compiler output: ------ expr.d(3): Error: alias op = op; cannot alias itself, use a qualified name to create an overload set expr.d(17): while looking for match for evaluate!op ------ This error is very strange, because 'op' is supposed to be a local symbol in the scope of the foreach, so why does it clash with the 'op' in the 'alias op' parameter of genCtEvaluate.evaluate? Furthermore, renaming the alias parameter, e.g., to `alias _op` elicits this even stranger error message: ------ expr.d(17): Error: undefined identifier op expr.d(17): while looking for match for evaluate!op ------ Very odd, since op is declared right in the line above as the foreach loop variable. Also, this strange behaviour goes away if the `void evaluate() {}` overload is commented out. This is a recent regression, though I haven't compiled the unreduced version of this code for a while now, so not 100% sure exactly when the regression was introduced. For sure it works back in 2.079.0.

Git bisect found the bad commit: 3e22ae81b18d6caa57865aaa3e0d48ea6678903a (dmd PR #9769 - fix issue 9029).

@StianGulpen created dlang/dmd pull request #10599 "fix issue 19884 - [regression] Error: alias op = op; cannot alias its…" fixing this issue: - fix issue 19884 - [regression] Error: alias op = op; cannot alias itself, use a qualified name to create an overload set https://github.com/dlang/dmd/pull/10599

dlang/dmd pull request #10599 "fix issue 19884 - [regression] Error: alias op = op; cannot alias its…" was merged into stable: - 2bf46b6365843868b465954077d6a4a09c023d45 by Stian Gulpen: fix issue 19884 - [regression] Error: alias op = op; cannot alias itself, use a qualified name to create an overload set https://github.com/dlang/dmd/pull/10599