Spurious imports in Phobos ?

[Somedude]

Hello,

When I display the dependencies with "dmd -deps=depends", I see that
simply importing std.stdio imports dozens of modules, among which
std.ranges, std.datetime, std.c.windows.winsock, std.regex, etc
In fact, the depends file is 433 lines long.

I noticed that std.string imports quite a lot of stuff.
Here is a copypasta of the code:

import core.exception : onRangeError;
import core.vararg, core.stdc.stdlib, core.stdc.string,
    std.algorithm, std.ascii, std.conv, std.exception, std.format,
std.functional,
    std.metastrings, std.range, std.regex, std.traits,
    std.typetuple, std.uni, std.utf;

//Remove when repeat is finally removed. They're only here as part of the
//deprecation of these functions in std.string.
public import std.algorithm : startsWith, endsWith, cmp, count;
public import std.array : join, split;

So as an experiment, I tried to remove a few imports:

std.range, std.regex, std.traits and std.algorithm
as well as the two lines of public import.

To my surprise, it still compiles !
The depends file goes down to 402 lines, but the executable size is
understandably not reduced because all the removed dependencies are
still used elsewhere.

Then I thought this may be due to public imports from other modules,
which makes me think that public imports are a bad idea, as we can
compile a module only because we imported unknowingly a namespace from
imported modules.

My question is: how do we know if std.range, std.regex, std.traits and
std.algorithm are spurious imports or if we can (and threfore should)
remove them safely from std.string ?

Dude