lib.attrsets.matchAttrs: Avoid some list allocations when walking structure
Benchmarks (`nix-instantiate ./. -A python3`): - Before: ``` json { "cpuTime": 0.29049500823020935, "envs": { "bytes": 4484216, "elements": 221443, "number": 169542 }, "gc": { "heapSize": 402915328, "totalBytes": 53086800 }, "list": { "bytes": 749424, "concats": 4242, "elements": 93678 }, "nrAvoided": 253991, "nrFunctionCalls": 149848, "nrLookups": 49612, "nrOpUpdateValuesCopied": 1587837, "nrOpUpdates": 10104, "nrPrimOpCalls": 130356, "nrThunks": 358981, "sets": { "bytes": 30423600, "elements": 1859999, "number": 41476 }, "sizes": { "Attr": 16, "Bindings": 16, "Env": 16, "Value": 24 }, "symbols": { "bytes": 236145, "number": 24453 }, "values": { "bytes": 10502520, "number": 437605 } } ``` - After: ``` json { "cpuTime": 0.2946169972419739, "envs": { "bytes": 3315224, "elements": 172735, "number": 120834 }, "gc": { "heapSize": 402915328, "totalBytes": 48718432 }, "list": { "bytes": 347568, "concats": 4242, "elements": 43446 }, "nrAvoided": 173252, "nrFunctionCalls": 101140, "nrLookups": 73595, "nrOpUpdateValuesCopied": 1587837, "nrOpUpdates": 10104, "nrPrimOpCalls": 83067, "nrThunks": 304216, "sets": { "bytes": 29704096, "elements": 1831673, "number": 24833 }, "sizes": { "Attr": 16, "Bindings": 16, "Env": 16, "Value": 24 }, "symbols": { "bytes": 236145, "number": 24453 }, "values": { "bytes": 8961552, "number": 373398 } } ```
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@ -883,7 +883,10 @@ rec {
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recursiveUpdateUntil (path: lhs: rhs: !(isAttrs lhs && isAttrs rhs)) lhs rhs;
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/* Returns true if the pattern is contained in the set. False otherwise.
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/*
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Recurse into every attribute set of the first argument and check that:
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- Each attribute path also exists in the second argument.
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- If the attribute's value is not a nested attribute set, it must have the same value in the right argument.
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Example:
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matchAttrs { cpu = {}; } { cpu = { bits = 64; }; }
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@ -895,16 +898,24 @@ rec {
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matchAttrs =
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# Attribute set structure to match
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pattern:
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# Attribute set to find patterns in
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# Attribute set to check
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attrs:
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assert isAttrs pattern;
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all id (attrValues (zipAttrsWithNames (attrNames pattern) (n: values:
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let pat = head values; val = elemAt values 1; in
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if length values == 1 then false
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else if isAttrs pat then isAttrs val && matchAttrs pat val
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else pat == val
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) [pattern attrs]));
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all
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( # Compare equality between `pattern` & `attrs`.
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attr:
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# Missing attr, not equal.
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attrs ? ${attr} && (
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let
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lhs = pattern.${attr};
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rhs = attrs.${attr};
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in
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# If attrset check recursively
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if isAttrs lhs then isAttrs rhs && matchAttrs lhs rhs
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else lhs == rhs
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)
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)
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(attrNames pattern);
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/* Override only the attributes that are already present in the old set
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useful for deep-overriding.
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@ -831,6 +831,26 @@ runTests {
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};
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};
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testMatchAttrsMatchingExact = {
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expr = matchAttrs { cpu = { bits = 64; }; } { cpu = { bits = 64; }; };
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expected = true;
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};
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testMatchAttrsMismatch = {
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expr = matchAttrs { cpu = { bits = 128; }; } { cpu = { bits = 64; }; };
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expected = false;
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};
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testMatchAttrsMatchingImplicit = {
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expr = matchAttrs { cpu = { }; } { cpu = { bits = 64; }; };
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expected = true;
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};
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testMatchAttrsMissingAttrs = {
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expr = matchAttrs { cpu = {}; } { };
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expected = false;
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};
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testOverrideExistingEmpty = {
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expr = overrideExisting {} { a = 1; };
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expected = {};
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