Last good Nixpkgs for Weston+nouveau? archive

I came this commit hash to terwiz[m] on IRC, who is trying to figure out
what the last version of Spectrum that worked on their NUC with Nvidia
graphics is.

1 files changed, 91 insertions, 0 deletions

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+# Option Definitions {#sec-option-definitions}
+
+Option definitions are generally straight-forward bindings of values to
+option names, like
+
+```nix
+config = {
+  services.httpd.enable = true;
+};
+```
+
+However, sometimes you need to wrap an option definition or set of
+option definitions in a *property* to achieve certain effects:
+
+## Delaying Conditionals {#sec-option-definitions-delaying-conditionals .unnumbered}
+
+If a set of option definitions is conditional on the value of another
+option, you may need to use `mkIf`. Consider, for instance:
+
+```nix
+config = if config.services.httpd.enable then {
+  environment.systemPackages = [ ... ];
+  ...
+} else {};
+```
+
+This definition will cause Nix to fail with an "infinite recursion"
+error. Why? Because the value of `config.services.httpd.enable` depends
+on the value being constructed here. After all, you could also write the
+clearly circular and contradictory:
+
+```nix
+config = if config.services.httpd.enable then {
+  services.httpd.enable = false;
+} else {
+  services.httpd.enable = true;
+};
+```
+
+The solution is to write:
+
+```nix
+config = mkIf config.services.httpd.enable {
+  environment.systemPackages = [ ... ];
+  ...
+};
+```
+
+The special function `mkIf` causes the evaluation of the conditional to
+be "pushed down" into the individual definitions, as if you had written:
+
+```nix
+config = {
+  environment.systemPackages = if config.services.httpd.enable then [ ... ] else [];
+  ...
+};
+```
+
+## Setting Priorities {#sec-option-definitions-setting-priorities .unnumbered}
+
+A module can override the definitions of an option in other modules by
+setting a *priority*. All option definitions that do not have the lowest
+priority value are discarded. By default, option definitions have
+priority 1000. You can specify an explicit priority by using
+`mkOverride`, e.g.
+
+```nix
+services.openssh.enable = mkOverride 10 false;
+```
+
+This definition causes all other definitions with priorities above 10 to
+be discarded. The function `mkForce` is equal to `mkOverride 50`.
+
+## Merging Configurations {#sec-option-definitions-merging .unnumbered}
+
+In conjunction with `mkIf`, it is sometimes useful for a module to
+return multiple sets of option definitions, to be merged together as if
+they were declared in separate modules. This can be done using
+`mkMerge`:
+
+```nix
+config = mkMerge
+  [ # Unconditional stuff.
+    { environment.systemPackages = [ ... ];
+    }
+    # Conditional stuff.
+    (mkIf config.services.bla.enable {
+      environment.systemPackages = [ ... ];
+    })
+  ];
+```