Merge pull request #5232 from sellout/doc-nix-cache

Author: aryairani

development.markdown

@@ -22,7 +22,7 @@ We use 0.5.0.1 of Ormolu and CI will add an extra commit, if needed, to autoform
 
 Also note that you can always wrap a comment around some code you don't want Ormolu to touch, using:
 
-```
+```haskell
 {- ORMOLU_DISABLE -}
 dontFormatMe = do blah
                     blah
@@ -96,11 +96,13 @@ This codebase uses symlinks as a workaround for some inconveniences in the `here
 
 First you'll need to enable "Developer Mode" in your Windows settings.
 
-	See https://consumer.huawei.com/en/support/content/en-us15594140/
+> See https://consumer.huawei.com/en/support/content/en-us15594140/
 
 Then you'll need to enable symlink support in your `git` configuration, e.g.
 
-    `git config core.symlinks true`
+```shell
+git config core.symlinks true
+```
 
 And then ask `git` to fix up your symlinks with `git checkout .`
 
@@ -113,10 +115,41 @@ Stack doesn't work deterministically in Windows due to mismatched expectations a
 
 ## Building with Nix
 
+__NB__: It is important that the Unison Nix cache is trusted when building, otherwise you will likely end up building hundreds of packages, including GHC itself.
+
+The recommended way to do this is to add the public key and URL for the cache to your system’s Nix configuration. /etc/nix/nix.conf should have lines similar to
+```conf
+trusted-public-keys = unison.cachix.org-1:i1DUFkisRPVOyLp/vblDsbsObmyCviq/zs6eRuzth3k=
+trusted-substituters = https://unison.cachix.org
+```
+these lines could be prefixed with `extra-` and they may have additional entries besides the ones for our cache.
+
+This command should work if you don’t want to edit the file manually:
+```shell
+sudo sh -c 'echo "extra-trusted-public-keys = unison.cachix.org-1:i1DUFkisRPVOyLp/vblDsbsObmyCviq/zs6eRuzth3k=
+extra-trusted-substituters = https://unison.cachix.org" >>/etc/nix/nix.conf'
+```
+After updating /etc/nix/nix.conf, you need to restart the Nix daemon. To do this on
+- Ubuntu: `sudo systemctl restart nix-daemon`
+- MacOS:
+    ```shell
+    sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist
+    sudo launchctl load /Library/LaunchDaemons/org.nixos.nix-daemon.plist
+    ```
+
+If you use NixOS, you may instead add this via your configuration.nix with
+```nix
+nix.settings.trusted-public-keys = ["unison.cachix.org-1:i1DUFkisRPVOyLp/vblDsbsObmyCviq/zs6eRuzth3k="];
+nix.settings.trusted-substituters = ["https://unison.cachix.org"];
+```
+and run `sudo nixos-rebuild switch` afterward.
+
+It is _not_ recommended to add your user to `trusted-users`. This _can_ make enabling flake configurations simpler (like the Unison Nix cache here), but [it is equivalent to giving that user root access (without need for sudo)](https://nix.dev/manual/nix/2.23/command-ref/conf-file.html#conf-trusted-users).
+
 ## Building package components with nix
 
 ### Build the unison executable
-```
+```shell
 nix build
 ```
 
@@ -125,7 +158,7 @@ This is specified with the normal
 `<package>:<component-type>:<component-name>` triple.
 
 Some examples:
-```
+```shell
 nix build '.#component-unison-cli:lib:unison-cli'
 nix build '.#component-unison-syntax:test:syntax-tests'
 nix build '.#component-unison-cli:exe:transcripts'
@@ -143,7 +176,7 @@ include:
 - ormolu
 - haskell-language-server
 
-```
+```shell
 nix develop
 ```
 
@@ -153,7 +186,7 @@ versions of the compiler and other development tools. Additionally,
 all non-local haskell dependencies (including profiling dependencies)
 are provided in the nix shell.
 
-```
+```shell
 nix develop '.#cabal-local'
 ```
 
@@ -163,17 +196,17 @@ versions of the compiler and other development tools. Additionally,
 all haskell dependencies of this package are provided by the nix shell
 (including profiling dependencies).
 
-```
+```shell
 nix develop '.#cabal-<package-name>'
 ```
 
 for example:
 
-```
+```shell
 nix develop '.#cabal-unison-cli'
 ```
 or
-```
+```shell
 nix develop '.#cabal-unison-parser-typechecker'
 ```
 
@@ -182,7 +215,7 @@ want to profile `unison-cli-main:exe:unison` then you could get into one of thes
 shells, cd into its directory, then run the program with
 profiling.
 
-```
+```shell
 nix develop '.#cabal-unison-parser-typechecker'
 cd unison-cli
 cabal run --enable-profiling unison-cli-main:exe:unison -- +RTS -p