When we do something like 'nix flake update --override-input nixpkgs
...', the override is now kept on subsequent calls. (If you don't want
this behaviour, you can use --no-write-lock-file.)
This fetchers copies a plain directory (i.e. not a Git/Mercurial
repository) to the store (or does nothing if the path is already a
store path).
One use case is to pin the 'nixpkgs' flake used to build the current
NixOS system, and prevent it from being garbage-collected, via a
system registry entry like this:
{
"from": {
"id": "nixpkgs",
"type": "indirect"
},
"to": {
"type": "path",
"path": "/nix/store/rralhl3wj4rdwzjn16g7d93mibvlr521-source",
"lastModified": 1585388205,
"rev": "b0c285807d6a9f1b7562ec417c24fa1a30ecc31a"
},
"exact": true
}
Note the fake "lastModified" and "rev" attributes that ensure that the
flake gives the same evaluation results as the corresponding
Git/GitHub inputs.
An example use is for pinning the "nixpkgs" entry the system-wide
registry to a particular store path. Inexact matches
(e.g. "nixpkgs/master") should still use the global registry.
One application for this is pinning the 'nixpkgs' flake to the exact
revision used to build the NixOS system, e.g.
{
"flakes": [
{
"from": {
"id": "nixpkgs",
"type": "indirect"
},
"to": {
"owner": "NixOS",
"repo": "nixpkgs",
"type": "github",
"rev": "b0c285807d6a9f1b7562ec417c24fa1a30ecc31a"
}
}
],
"version": 2
}
This is now done in a single pass. Also fixes some issues when
updating flakes with circular dependencies. Finally, when using
'--recreate-lock-file --commit-lock-file', the commit message now
correctly shows the differences.
The install-multi-user script uses blue, green, and red colors, as
well as bold and underline, to add helpful formatting that helps
structure its rather voluminous output.
Unfortunately, the terminal escape sequences it uses are not quite
well-formed. The relevant information is all there, just obscured
by some extra noise, a leading parameter `38`. Empirically, the
result is:
* On macOS, in both Terminal.app and iTerm2, the spurious `38` is
ignored, the rest of the escape sequence is applied, and the colors
show up as intended.
* On Linux, in at least gnome-terminal and xterm, the spurious `38`
and the next parameter after it are ignored, and what's left is
applied. So in the sequence `38;4;32`, the 4 (underline) is
ignored but the 32 (green) takes effect; in a more typical sequence
like `38;34`, the 34 (blue) is ignored and nothing happens.
These codes are all unchanged since this script's origins as a
Darwin-only script -- so the fact that they work fine in common macOS
terminals goes some way to explain how the bug arose.
Happily, we can make the colors work as intended by just deleting the
extra `38;`. Tested in all four terminals mentioned above; the new
codes work correctly on all of them, and on the two macOS terminals
they work exactly the same as before.
---
In a bit more technical detail -- perhaps more than anyone, me
included, ever wanted to know, but now that I've gone and learned it
I'll write it down anyway :) -- here's what's happening in these codes:
An ECMA-48 "control sequence" begins with `\033[` aka "CSI", contains
any number of parameters as semicolon-separated decimal numbers (plus
sometimes other wrinkles), and ends with a byte from 0x40..0x7e. In
our case, with `m` aka "SGR", "Select Graphic Rendition".
An SGR control sequence `\033[...m` sets colors, fonts, text styles,
etc. In particular a parameter `31` means red, `32` green, `34` blue,
`4` underline, and `0` means reset to normal. Those are all we use.
There is also a `38`. This is used for setting colors too... but it
needs arguments. `38;5;nn` is color nn from a 256-color palette, and
`38;2;rr;gg;bb` has the given RGB values.
There is no meaning defined for `38;1` or `38;34` etc. On seeing a
parameter `38` followed by an unrecognized argument for it, apparently
some implementations (as seen on macOS) discard only the `38` and
others (as seen on Linux) discard the argument too before resuming.
