Check your (named) imports for unused or underused ones.
And new: check your (built-in) variables also.

Usage:

--f              scan multiple or one file(s)
--d              scan a whole path
--iuse           for the minimal import use (default is 1)
--info           for used lines
--varUse         detect unused / underused built-in variables (alpha state)
--vuse           for the minimal variable use (default is 1)

test.d:

module test;
import std.stdio;
public {
import std.file : read;
import std.string : format, strip;
}
import std.array : split, join, empty;
import std.algorithm : startsWith, endsWith;
bool isEmpty(string test) {
return test.strip().empty();
}
private void _foo() { }
string fmt() {
return format("%d.%d.%d", 0, 9, 9);
}

Checked with: DAT --f test.d --use 2 --info

* test.d
        Named import std.string : format imported on line 6 is used 1 times. On lines: [18]
        Named import std.string : strip imported on line 6 is used 1 times. On lines: [12]
        Named import std.algorithm : startsWith imported on line 9 is never used.
        Named import std.algorithm : endsWith imported on line 9 is never used.
         - Therefore it is useless to import std.algorithm
        Named import std.array : split imported on line 8 is never used.
        Named import std.array : join imported on line 8 is never used.
        Named import std.array : empty imported on line 8 is used 1 times. On lines: [12]
        Named import std.file : read imported on line 5 is never used.
         - But maybe 'read' is used in other modules. [public]

And for std/stdio.d checked with: DAT --f std/stdio.d --use 2 --info

* std/stdio.d
        Named import std.c.stdio : FHND_WCHAR imported on line 35 is used 1 times. On lines: [2504]

Unused/Underused built-in types

It's now possible (but still in progress) to detect unused/underused built-in types.

Therefore you can use the --varUse and --vuse arguments.

Dgame/SimpleDAT

Unused/Underused built-in types