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