These only functioned if a very narrow combination of conditions held:
- The result path does not yet exist (--check did not result in
repeated builds), AND
- The result path is not available from any configured substituters, AND
- No remote builders that can build the path are available.
If any of these do not hold, a derivation would be built 0 or 1 times
regardless of the repeat option. Thus, remove it to avoid confusion.
being too specific about it requires more maintenance (or otherwise
produced more confusion and churn), since these points of contact change
over time.
this is a quick half-fix for command line examples, as discussed
discussed in [1].
[1]: https://github.com/NixOS/nix/pull/7389
examples which look like this
$ foo bar
baz
are confusing for Unix shell beginners, because it's hard to discern
what is supposed to be entered into the actual command line when the
convention of prefixing `$` is not known, as barely any real-world shell
looks that way any more.
this change prevents selecting the prompt part with the mouse in the
HTML representation of the Nix manual.
it does not prevent selecting the output part of the shell example.
it also does not address that the copy button provided by mdBook takes
the entire sample, including the prompts, into the clipboard.
The old way was not correct.
Here is an example:
```
$ nix-instantiate --eval --expr 'let x = a: throw "asdf"; in x 1' --show-trace
error: asdf
… while evaluating 'x'
at «string»:1:9:
1| let x = a: throw "asdf"; in x 1
| ^
… from call site
at «string»:1:29:
1| let x = a: throw "asdf"; in x 1
| ^
```
and yet also:
```
$ nix-instantiate --eval --expr 'let x = a: throw "asdf"; in x' --show-trace
<LAMBDA>
```
Here is the thing: in both cases we are evaluating `x`!
Nix is a higher-order languages, and functions are a sort of value. When
we write `x = a: ...`, `a: ...` is the expression that `x` is being
defined to be, and that is already a value. Therefore, we should *never*
get an trace that says "while evaluating `x`", because evaluating `a:
...` is *trival* and nothing happens during it!
What is actually happening here is we are applying `x` and evaluating
its *body* with arguments substituted for parameters. I think the
simplest way to say is just "while *calling* `x`", and so that is what I
changed it to.
Linus Heckemann
Jörg Thalheim