https://issues.dlang.org/show_bug.cgi?id=23576

          Issue ID: 23576
           Summary: Better Error Message When Forgetting To Pass A
                    Template Parameter
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: jack@jackstouffer.com

Current Behavior

Consider the following program

import std;

void test1(uint id, uint __)
{
    int x = 0;
}

void test2(C)(uint id)
{
    int x = 0;
}

void main()
{
    uint a = 0;
    test1(a);
    test2(a);
}

For test1, DMD gives a good error message:

onlineapp.d(16): Error: function `onlineapp.test1(uint id, uint __)` is not
callable using argument types `(uint)`
onlineapp.d(16):        missing argument for parameter #2: `uint __`

This tells the user exactly what's wrong. Great! On the other hand, the test2 error message isn't as helpful

onlineapp.d(17): Error: none of the overloads of template `onlineapp.test2` are
callable using argument types `!()(uint)`
onlineapp.d(8):        Candidate is: `test2(C)(uint id)`

Expected Behavior:

The error message should be something like

onlineapp.d(16): Error: function `onlineapp.test2(C)(uint id)` is not callable
using argument types `(uint)`
onlineapp.d(16):        missing argument for template parameter #1: `C`

--