The function isn't being used anywhere so it seems safe to remove

No need to use `c_str()` in combination with `ASSERT_STREQ`.
It's possible to just use ASSERT_EQ on std::string

This is a proof on concept to evaluate writing unit tests for Nix using
google test (https://github.com/google/googletest).

In order to execute tests:

$ make unit-tests
$ ./unit-tests

The Makefile rules for `unit-tests` is a complete hack.

builtins.readFile: do not truncate content

Improve help-message for nix-repl

Use fragment size for autoGC capacity calculation

This reverts commit 3ebfbecd, reversing
changes made to c089c52d.

https://github.com/NixOS/nix/pull/3558

remote-store: don't log raw stderr by default

The raw stderr output isn't logged anymore so the build logs need to be
printed by the default logger in order for the old commands like
nix-build to still show build output.

For remote stores the log messages are already forwarded as structured
STDERR_RESULT messages so the old format is duplicate information.  But
still included with -vvv since it could be useful for debugging
problems.

    $ nix build -L /nix/store/nl71b2niws857ffiaggyrkjwgx9jjzc0-foo.drv --store ssh-ng://localhost
    Hello World!
    foo> Hello World!
    [1/0/1 built] building foo

Fixes #3556

* Remove obsolete `printHelp` function
* Add an example to demonstrate how to list all available commands
  within the REPL

(cherry picked from commit f459ca54)

(cherry picked from commit 5d8504b9)

(cherry picked from commit bc5d4843)

Revamp README.md

Co-authored-by: worldofpeace <worldofpeace@protonmail.ch>

Co-authored-by: worldofpeace <worldofpeace@protonmail.ch>

This avoids inheriting the caller's shellHook, which can happen when
running a dev-shell inside a dev-shell.

Tested against https://github.com/NixOS/nixpkgs/pull/72074.

Fixes #3540.

Fix displaying error-position in `builtins.fetch{Tree,Tarball}`

Without dereferencing this pointer, you'd get an error like this:

```
error: unsupported argument 'abc' to 'fetchTarball', at 0x13627e8
```

When used with `readFile`, we have a pretty good heuristic of the file
size, so `reserve` this in the `string`. This will save some allocation
/ copy when the string is growing.

Now it is always `drain` (see previous commit).

Only call grantpt on MacOS systems