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author | Profpatsch <mail@profpatsch.de> | 2021-01-01T13·52+0100 |
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committer | Profpatsch <mail@profpatsch.de> | 2021-01-01T19·03+0000 |
commit | 4618b57f74e9a26caaf4a5a4943345c3d4cb2d4c (patch) | |
tree | 5e1fb907b0cd7be52780d5804db2813cc59a3b68 /nix/mergePatch | |
parent | 1686355d2e26281e5ccf5bc0fec74820b542856d (diff) |
feat(nix): add mergePatch r/2040
Change-Id: Id6a9ecbfb04886e6d96750b1451c29dc3f68154e Reviewed-on: https://cl.tvl.fyi/c/depot/+/2307 Tested-by: BuildkiteCI Reviewed-by: lukegb <lukegb@tvl.fyi>
Diffstat (limited to '')
-rw-r--r-- | nix/mergePatch/default.nix | 186 |
1 files changed, 186 insertions, 0 deletions
diff --git a/nix/mergePatch/default.nix b/nix/mergePatch/default.nix new file mode 100644 index 000000000000..0f80b93d4c65 --- /dev/null +++ b/nix/mergePatch/default.nix @@ -0,0 +1,186 @@ +{ 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; +} |