lib.strings: init splitStringBy (#385643) (a9320986) · Commits · nix / nixpkgs

lib/default.nix

+1 −0

Original line number	Diff line number	Diff line
		@@ -347,6 +347,7 @@ let
		toSentenceCase
		addContextFrom
		splitString
		splitStringBy
		removePrefix
		removeSuffix
		versionOlder

lib/strings.nix

+91 −0

Original line number	Diff line number	Diff line
		@@ -1592,6 +1592,97 @@ rec {
		in
		map (addContextFrom s) splits;

		/**
		Splits a string into substrings based on a predicate that examines adjacent characters.

		This function provides a flexible way to split strings by checking pairs of characters
		against a custom predicate function. Unlike simpler splitting functions, this allows
		for context-aware splitting based on character transitions and patterns.

		# Inputs

		`predicate`
		: Function that takes two arguments (previous character and current character)
		and returns true when the string should be split at the current position.
		For the first character, previous will be "" (empty string).

		`keepSplit`
		: Boolean that determines whether the splitting character should be kept as
		part of the result. If true, the character will be included at the beginning
		of the next substring; if false, it will be discarded.

		`str`
		: The input string to split.

		# Return

		A list of substrings from the original string, split according to the predicate.

		# Type

		```
		splitStringBy :: (string -> string -> bool) -> bool -> string -> [string]
		```

		# Examples
		:::{.example}
		## `lib.strings.splitStringBy` usage example

		Split on periods and hyphens, discarding the separators:
		```nix
		splitStringBy (prev: curr: builtins.elem curr [ "." "-" ]) false "foo.bar-baz"
		=> [ "foo" "bar" "baz" ]
		```

		Split on transitions from lowercase to uppercase, keeping the uppercase characters:
		```nix
		splitStringBy (prev: curr: builtins.match "[a-z]" prev != null && builtins.match "[A-Z]" curr != null) true "fooBarBaz"
		=> [ "foo" "Bar" "Baz" ]
		```

		Handle leading separators correctly:
		```nix
		splitStringBy (prev: curr: builtins.elem curr [ "." ]) false ".foo.bar.baz"
		=> [ "" "foo" "bar" "baz" ]
		```

		Handle trailing separators correctly:
		```nix
		splitStringBy (prev: curr: builtins.elem curr [ "." ]) false "foo.bar.baz."
		=> [ "foo" "bar" "baz" "" ]
		```
		:::
		*/
		splitStringBy =
		predicate: keepSplit: str:
		let
		len = stringLength str;

		# Helper function that processes the string character by character
		go =
		pos: currentPart: result:
		# Base case: reached end of string
		if pos == len then
		result ++ [ currentPart ]
		else
		let
		currChar = substring pos 1 str;
		prevChar = if pos > 0 then substring (pos - 1) 1 str else "";
		isSplit = predicate prevChar currChar;
		in
		if isSplit then
		# Split here - add current part to results and start a new one
		let
		newResult = result ++ [ currentPart ];
		newCurrentPart = if keepSplit then currChar else "";
		in
		go (pos + 1) newCurrentPart newResult
		else
		# Keep building current part
		go (pos + 1) (currentPart + currChar) result;
		in
		if len == 0 then [ (addContextFrom str "") ] else map (addContextFrom str) (go 0 "" [ ]);

		/**
		Return a string without the specified prefix, if the prefix matches.

lib/tests/misc.nix

+95 −0

Original line number	Diff line number	Diff line
		@@ -631,6 +631,101 @@ runTests {
		];
		};

		testSplitStringBySimpleDelimiter = {
		expr = strings.splitStringBy (
		prev: curr:
		builtins.elem curr [
		"."
		"-"
		]
		) false "foo.bar-baz";
		expected = [
		"foo"
		"bar"
		"baz"
		];
		};

		testSplitStringByLeadingDelimiter = {
		expr = strings.splitStringBy (prev: curr: builtins.elem curr [ "." ]) false ".foo.bar.baz";
		expected = [
		""
		"foo"
		"bar"
		"baz"
		];
		};

		testSplitStringByTrailingDelimiter = {
		expr = strings.splitStringBy (prev: curr: builtins.elem curr [ "." ]) false "foo.bar.baz.";
		expected = [
		"foo"
		"bar"
		"baz"
		""
		];
		};

		testSplitStringByMultipleConsecutiveDelimiters = {
		expr = strings.splitStringBy (prev: curr: builtins.elem curr [ "." ]) false "foo...bar";
		expected = [
		"foo"
		""
		""
		"bar"
		];
		};

		testSplitStringByKeepingSplitChar = {
		expr = strings.splitStringBy (prev: curr: builtins.elem curr [ "." ]) true "foo.bar.baz";
		expected = [
		"foo"
		".bar"
		".baz"
		];
		};

		testSplitStringByCaseTransition = {
		expr = strings.splitStringBy (
		prev: curr: builtins.match "[a-z]" prev != null && builtins.match "[A-Z]" curr != null
		) true "fooBarBaz";
		expected = [
		"foo"
		"Bar"
		"Baz"
		];
		};

		testSplitStringByEmptyString = {
		expr = strings.splitStringBy (prev: curr: builtins.elem curr [ "." ]) false "";
		expected = [ "" ];
		};

		testSplitStringByComplexPredicate = {
		expr = strings.splitStringBy (
		prev: curr:
		prev != ""
		&& curr != ""
		&& builtins.match "[0-9]" prev != null
		&& builtins.match "[a-z]" curr != null
		) true "123abc456def";
		expected = [
		"123"
		"abc456"
		"def"
		];
		};

		testSplitStringByUpperCaseStart = {
		expr = strings.splitStringBy (prev: curr: builtins.match "[A-Z]" curr != null) true "FooBarBaz";
		expected = [
		""
		"Foo"
		"Bar"
		"Baz"
		];
		};

		testEscapeShellArg = {
		expr = strings.escapeShellArg "esc'ape\nme";
		expected = "'esc'\\''ape\nme'";

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