nixpkgs/lib/strings-with-deps.nix
Robert Hensing afa6c51f27 lib: Use Nix's static scope checking, fix error message, optimize
Nix can perform static scope checking, but whenever code is inside
a `with` expression, the analysis breaks down, because it can't
know statically what's in the attribute set whose attributes were
brought into scope. In those cases, Nix has to assume that
everything works out.

Except it doesnt. Removing `with` from lib/ revealed an undefined
variable in an error message.

If that doesn't convince you that we're better off without `with`,
I can tell you that this PR results in a 3% evaluation performance
improvement because Nix can look up local variables by index.
This adds up with applications like the module system.

Furthermore, removing `with` makes the binding site of each
variable obvious, which helps with comprehension.
2020-10-22 13:46:47 +02:00

85 lines
2.5 KiB
Nix

{ lib }:
/*
Usage:
You define you custom builder script by adding all build steps to a list.
for example:
builder = writeScript "fsg-4.4-builder"
(textClosure [doUnpack addInputs preBuild doMake installPhase doForceShare]);
a step is defined by noDepEntry, fullDepEntry or packEntry.
To ensure that prerequisite are met those are added before the task itself by
textClosureDupList. Duplicated items are removed again.
See trace/nixpkgs/trunk/pkgs/top-level/builder-defs.nix for some predefined build steps
Attention:
let
pkgs = (import <nixpkgs>) {};
in let
inherit (pkgs.stringsWithDeps) fullDepEntry packEntry noDepEntry textClosureMap;
inherit (pkgs.lib) id;
nameA = noDepEntry "Text a";
nameB = fullDepEntry "Text b" ["nameA"];
nameC = fullDepEntry "Text c" ["nameA"];
stages = {
nameHeader = noDepEntry "#! /bin/sh \n";
inherit nameA nameB nameC;
};
in
textClosureMap id stages
[ "nameHeader" "nameA" "nameB" "nameC"
nameC # <- added twice. add a dep entry if you know that it will be added once only [1]
"nameB" # <- this will not be added again because the attr name (reference) is used
]
# result: Str("#! /bin/sh \n\nText a\nText b\nText c\nText c",[])
[1] maybe this behaviour should be removed to keep things simple (?)
*/
let
inherit (lib)
concatStringsSep
head
isAttrs
listToAttrs
tail
;
in
rec {
/* !!! The interface of this function is kind of messed up, since
it's way too overloaded and almost but not quite computes a
topological sort of the depstrings. */
textClosureList = predefined: arg:
let
f = done: todo:
if todo == [] then {result = []; inherit done;}
else
let entry = head todo; in
if isAttrs entry then
let x = f done entry.deps;
y = f x.done (tail todo);
in { result = x.result ++ [entry.text] ++ y.result;
done = y.done;
}
else if done ? ${entry} then f done (tail todo)
else f (done // listToAttrs [{name = entry; value = 1;}]) ([predefined.${entry}] ++ tail todo);
in (f {} arg).result;
textClosureMap = f: predefined: names:
concatStringsSep "\n" (map f (textClosureList predefined names));
noDepEntry = text: {inherit text; deps = [];};
fullDepEntry = text: deps: {inherit text deps;};
packEntry = deps: {inherit deps; text="";};
stringAfter = deps: text: { inherit text deps; };
}