feat(nix): add mergePatch

Change-Id: Id6a9ecbfb04886e6d96750b1451c29dc3f68154e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2307
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>
This commit is contained in:
Profpatsch 2021-01-01 14:52:54 +01:00
parent 1686355d2e
commit 4618b57f74

186
nix/mergePatch/default.nix Normal file
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{ lib, depot, ... }:
/*
JSON Merge-Patch for nix
Spec: https://tools.ietf.org/html/rfc7396
An algorithm for changing and removing fields in nested objects.
For example, given the following original document:
{
a = "b";
c = {
d = "e";
f = "g";
}
}
Changing the value of `a` and removing `f` can be achieved by merging the patch
{
a = "z";
c.f = null;
}
which results in
{
a = "z";
c = {
d = "e";
};
}
Pseudo-code:
define MergePatch(Target, Patch):
if Patch is an Object:
if Target is not an Object:
Target = {} # Ignore the contents and set it to an empty Object
for each Name/Value pair in Patch:
if Value is null:
if Name exists in Target:
remove the Name/Value pair from Target
else:
Target[Name] = MergePatch(Target[Name], Value)
return Target
else:
return Patch
*/
let
foldlAttrs = op: init: attrs:
lib.foldl' op init
(lib.mapAttrsToList lib.nameValuePair attrs);
mergePatch = target: patch:
if lib.isAttrs patch
then
let target' = if lib.isAttrs target then target else {};
in foldlAttrs
(acc: patchEl:
if patchEl.value == null
then removeAttrs acc [ patchEl.name ]
else acc // {
${patchEl.name} =
mergePatch
(acc.${patchEl.name} or "unnused")
patchEl.value;
})
target'
patch
else patch;
inherit (depot.nix.runTestsuite)
runTestsuite
it
assertEq
;
tests =
let
# example target from the RFC
testTarget = {
a = "b";
c = {
d = "e";
f = "g";
};
};
# example patch from the RFC
testPatch = {
a = "z";
c.f = null;
};
emptyPatch = it "the empty patch returns the original target" [
(assertEq "id"
(mergePatch testTarget {})
testTarget)
];
nonAttrs = it "one side is a non-attrset value" [
(assertEq "target is a value means the value is replaced by the patch"
(mergePatch 42 testPatch)
(mergePatch {} testPatch))
(assertEq "patch is a value means it replaces target alltogether"
(mergePatch testTarget 42)
42)
];
rfcExamples = it "the examples from the RFC" [
(assertEq "a subset is deleted and overwritten"
(mergePatch testTarget testPatch) {
a = "z";
c = {
d = "e";
};
})
(assertEq "a more complicated example from the example section"
(mergePatch {
title = "Goodbye!";
author = {
givenName = "John";
familyName = "Doe";
};
tags = [ "example" "sample" ];
content = "This will be unchanged";
} {
title = "Hello!";
phoneNumber = "+01-123-456-7890";
author.familyName = null;
tags = [ "example" ];
})
{
title = "Hello!";
phoneNumber = "+01-123-456-7890";
author = {
givenName = "John";
};
tags = [ "example" ];
content = "This will be unchanged";
})
];
rfcTests =
let
r = index: target: patch: res:
(assertEq "test number ${toString index}"
(mergePatch target patch)
res);
in it "the test suite from the RFC" [
(r 1 {"a" = "b";} {"a" = "c";} {"a" = "c";})
(r 2 {"a" = "b";} {"b" = "c";} {"a" = "b"; "b" = "c";})
(r 3 {"a" = "b";} {"a" = null;} {})
(r 4 {"a" = "b"; "b" = "c";}
{"a" = null;}
{"b" = "c";})
(r 5 {"a" = ["b"];} {"a" = "c";} {"a" = "c";})
(r 6 {"a" = "c";} {"a" = ["b"];} {"a" = ["b"];})
(r 7 {"a" = {"b" = "c";}; }
{"a" = {"b" = "d"; "c" = null;};}
{"a" = {"b" = "d";};})
(r 8 {"a" = [{"b" = "c";}];}
{"a" = [1];}
{"a" = [1];})
(r 9 ["a" "b"] ["c" "d"] ["c" "d"])
(r 10 {"a" = "b";} ["c"] ["c"])
(r 11 {"a" = "foo";} null null)
(r 12 {"a" = "foo";} "bar" "bar")
(r 13 {"e" = null;} {"a" = 1;} {"e" = null; "a" = 1;})
(r 14 [1 2]
{"a" = "b"; "c" = null;}
{"a" = "b";})
(r 15 {}
{"a" = {"bb" = {"ccc" = null;};};}
{"a" = {"bb" = {};};})
];
in runTestsuite "mergePatch" [
emptyPatch
nonAttrs
rfcExamples
rfcTests
];
in {
__functor = _: mergePatch;
inherit tests;
}