mdebray/tvl-depot
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Note recommended use of 'or' in override patterns

Browse source 
This fixes #6
This commit is contained in:
Vincent Ambo 2021-11-14 15:53:00 +03:00
parent 2a098e081b
commit a9a1a46458
1 changed files with 9 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

11
nix/nix-1p/README.md
View file

@ -549,7 +549,7 @@ like this:
```nix ```nix
someProgram.overrideAttrs(old: { someProgram.overrideAttrs(old: {
configureFlags = old.configureFlags ++ ["--mimic-threaten-tag"]; configureFlags = old.configureFlags or [] ++ ["--mimic-threaten-tag"];
}) })
``` ```
@ -557,6 +557,13 @@ This pattern has a variety of applications of varying complexity. The top-level
package set itself can have an `overlays` argument passed to it which may add package set itself can have an `overlays` argument passed to it which may add
new packages to the imported set. new packages to the imported set.
Note the use of the `or` operator to default to an empty list if the
original flags do not include `configureFlags`. This is required in
case a package does not set any flags by itself.
Since this can change in a package over time, it is useful to guard
against it using `or`.
For a slightly more advanced example, assume that we want to import `<nixpkgs>` For a slightly more advanced example, assume that we want to import `<nixpkgs>`
but have the modification above be reflected in the imported package set: but have the modification above be reflected in the imported package set:
@ -564,7 +571,7 @@ but have the modification above be reflected in the imported package set:
let let
overlay = (self: super: { overlay = (self: super: {
someProgram = super.someProgram.overrideAttrs(old: { someProgram = super.someProgram.overrideAttrs(old: {
configureFlags = old.configureFlags ++ ["--mimic-threaten-tag"]; configureFlags = old.configureFlags or [] ++ ["--mimic-threaten-tag"];
}); });
}); });
in import <nixpkgs> { overlays = [ overlay ]; } in import <nixpkgs> { overlays = [ overlay ]; }