* Atomically load the lowered program (#610)

Since we're atomically initializing the compiled program in
`Regex.Program`, we need to pair that with an atomic load.

Resolves #609.

* Add tests for line start/end word boundary diffs (#616)

The `default` and `simple` word boundaries have different behaviors
at the start and end of strings/lines. These tests validate that we
have the correct behavior implemented. Related to issue #613.

* Add tweaks for Android

* Fix documentation typo (#615)

* Fix abstract for Regex.dotMatchesNewlines(_:). (#614)

The old version looks like it was accidentally duplicated from
anchorsMatchLineEndings(_:) just below it.

* Remove `RegexConsumer` and fix its dependencies (#617)

* Remove `RegexConsumer` and fix its dependencies

This eliminates the RegexConsumer type and rewrites its users to call
through to other, existing functionality on Regex or in the Algorithms
implementations. RegexConsumer doesn't take account of the dual
subranges required for matching, so it can produce results that are
inconsistent with matches(of:) and ranges(of:), which were rewritten
earlier.

rdar://102841216

* Remove remaining from-end algorithm methods

This removes methods that are left over from when we were considering
from-end algorithms. These aren't tested and may not have the correct
semantics, so it's safer to remove them entirely.

* Improve StringProcessing and RegexBuilder documentation (#611)

This includes documentation improvements for core types/methods,
RegexBuilder types along with their generated variadic initializers,
and adds some curation. It also includes tests of the documentation
code samples.

* Set availability for inverted character class test (#621)

This feature depends on running with a Swift 5.7 stdlib, and fails
when that isn't available.

* Add type annotations in RegexBuilder tests

These changes work around a change to the way result builders are
compiled that removes the ability for result builder closure outputs
to affect the overload resolution elsewhere in an expression.

Workarounds for rdar://104881395 and rdar://104645543

* Workaround for fileprivate array issue

A recent compiler change results in fileprivate arrays sometimes
not keeping their buffers around long enough. This change avoids that
issue by removing the fileprivate annotations from the affected type.

* Fix an issue where named character classes weren't getting converted in the result builder. <rdar://104480703>

* Stop at end of search string in TwoWaySearcher (#631)

When searching for a substring that doesn't exist, it was possible
for TwoWaySearcher to advance beyond the end of the search string,
causing a crash. This change adds a `limitedBy:` parameter to that
index movement, avoiding the invalid movement.

Fixes rdar://105154010

* Correct misspelling in DSL renderer (#627)

vertial -> vertical

rdar://104602317

* Fix output type mismatch with RegexBuilder (#626)

Some regex literals (and presumably other `Regex` instances) lose
their output type information when used in a RegexBuilder closure due
to the way the concatenating builder calls are overloaded. In
particular, any output type with labeled tuples or where the sum of
tuple components in the accumulated and new output types is greater
than 10 will be ignored.

Regex internals don't make this distinction, however, so there ends up
being a mismatch between what a `Regex.Match` instance tries to
produce and the output type of the outermost regex. For example, this
code results in a crash, because `regex` is a `Regex<Substring>`
but the match tries to produce a `(Substring, number: Substring)`:

    let regex = Regex {
        ZeroOrMore(.whitespace)
        /:(?<number>\d+):/
        ZeroOrMore(.whitespace)
    }
    let match = try regex.wholeMatch(in: " :21: ")
    print(match!.output)

To fix this, we add a new `ignoreCapturesInTypedOutput` DSLTree node
to mark situations where the output type is discarded. This status
is propagated through the capture list into the match's storage,
which lets us produce the correct output type. Note that we can't just
drop the capture groups when building the compiled program because
(1) different parts of the regex might reference the capture group
and (2) all capture groups are available if a developer converts the
output to `AnyRegexOutput`.

    let anyOutput = AnyRegexOutput(match)
    // anyOutput[1] == "21"
    // anyOutput["number"] == Optional("21")

Fixes #625. rdar://104823356

Note: Linux seems to crash on different tests when the two customTest
overloads have `internal` visibility or are called. Switching one of the
functions to be generic over a RegexComponent works around the issue.

* Revert "Merge pull request #628 from apple/result_builder_changes_workaround"

This reverts commit 7e059b7, reversing
changes made to 3ca8b13.

* Use `some` syntax in variadics

This supports a type checker fix after the change in how result
builder closure parameters are type-checked.

* Type checker workaround: adjust test

* Further refactor to work around type checker regression

* Align availability macro with OS versions (#641)

* Speed up general character class matching (#642)

Short-circuit Character.isASCII checks inside built in character class matching.

Also, make benchmark try a few more times before giving up.

* Test for \s matching CRLF when scalar matching (#648)

* General ascii fast paths for character classes (#644)

General ASCII fast-paths for builtin character classes

* Remove the unsupported `anyScalar` case (#650)

We decided not to support the `anyScalar` character class, which would
match a single Unicode scalar regardless of matching mode. However,
its representation was still included in the various character class
types in the regex engine, leading to unreachable code and unclear
requirements when changing or adding new code. This change removes
that representation where possible.

The `DSLTree.Atom.CharacterClass` enum is left unchanged, since it
is marked `@_spi(RegexBuilder) public`. Any use of that enum case
is handled with a `fatalError("Unsupported")`, and it isn't produced
on any code path.

---------

Co-authored-by: Nate Cook <natecook@apple.com>
Co-authored-by: Butta <repo@butta.fastem.com>
Co-authored-by: Ole Begemann <ole@oleb.net>
Co-authored-by: Alex Martini <amartini@apple.com>
Co-authored-by: Alejandro Alonso <alejandro_alonso@apple.com>
Co-authored-by: David Ewing <dewing@apple.com>
Co-authored-by: Dave Ewing <96321608+DaveEwing@users.noreply.github.com>

* Atomically load the lowered program (#610)

Since we're atomically initializing the compiled program in
`Regex.Program`, we need to pair that with an atomic load.

Resolves #609.

* Add tests for line start/end word boundary diffs (#616)

The `default` and `simple` word boundaries have different behaviors
at the start and end of strings/lines. These tests validate that we
have the correct behavior implemented. Related to issue #613.

* Add tweaks for Android

* Fix documentation typo (#615)

* Fix abstract for Regex.dotMatchesNewlines(_:). (#614)

The old version looks like it was accidentally duplicated from
anchorsMatchLineEndings(_:) just below it.

* Remove `RegexConsumer` and fix its dependencies (#617)

* Remove `RegexConsumer` and fix its dependencies

This eliminates the RegexConsumer type and rewrites its users to call
through to other, existing functionality on Regex or in the Algorithms
implementations. RegexConsumer doesn't take account of the dual
subranges required for matching, so it can produce results that are
inconsistent with matches(of:) and ranges(of:), which were rewritten
earlier.

rdar://102841216

* Remove remaining from-end algorithm methods

This removes methods that are left over from when we were considering
from-end algorithms. These aren't tested and may not have the correct
semantics, so it's safer to remove them entirely.

* Improve StringProcessing and RegexBuilder documentation (#611)

This includes documentation improvements for core types/methods,
RegexBuilder types along with their generated variadic initializers,
and adds some curation. It also includes tests of the documentation
code samples.

* Set availability for inverted character class test (#621)

This feature depends on running with a Swift 5.7 stdlib, and fails
when that isn't available.

* Add type annotations in RegexBuilder tests

These changes work around a change to the way result builders are
compiled that removes the ability for result builder closure outputs
to affect the overload resolution elsewhere in an expression.

Workarounds for rdar://104881395 and rdar://104645543

* Workaround for fileprivate array issue

A recent compiler change results in fileprivate arrays sometimes
not keeping their buffers around long enough. This change avoids that
issue by removing the fileprivate annotations from the affected type.

* Fix an issue where named character classes weren't getting converted in the result builder. <rdar://104480703>

* Stop at end of search string in TwoWaySearcher (#631)

When searching for a substring that doesn't exist, it was possible
for TwoWaySearcher to advance beyond the end of the search string,
causing a crash. This change adds a `limitedBy:` parameter to that
index movement, avoiding the invalid movement.

Fixes rdar://105154010

* Correct misspelling in DSL renderer (#627)

vertial -> vertical

rdar://104602317

* Fix output type mismatch with RegexBuilder (#626)

Some regex literals (and presumably other `Regex` instances) lose
their output type information when used in a RegexBuilder closure due
to the way the concatenating builder calls are overloaded. In
particular, any output type with labeled tuples or where the sum of
tuple components in the accumulated and new output types is greater
than 10 will be ignored.

Regex internals don't make this distinction, however, so there ends up
being a mismatch between what a `Regex.Match` instance tries to
produce and the output type of the outermost regex. For example, this
code results in a crash, because `regex` is a `Regex<Substring>`
but the match tries to produce a `(Substring, number: Substring)`:

    let regex = Regex {
        ZeroOrMore(.whitespace)
        /:(?<number>\d+):/
        ZeroOrMore(.whitespace)
    }
    let match = try regex.wholeMatch(in: " :21: ")
    print(match!.output)

To fix this, we add a new `ignoreCapturesInTypedOutput` DSLTree node
to mark situations where the output type is discarded. This status
is propagated through the capture list into the match's storage,
which lets us produce the correct output type. Note that we can't just
drop the capture groups when building the compiled program because
(1) different parts of the regex might reference the capture group
and (2) all capture groups are available if a developer converts the
output to `AnyRegexOutput`.

    let anyOutput = AnyRegexOutput(match)
    // anyOutput[1] == "21"
    // anyOutput["number"] == Optional("21")

Fixes #625. rdar://104823356

Note: Linux seems to crash on different tests when the two customTest
overloads have `internal` visibility or are called. Switching one of the
functions to be generic over a RegexComponent works around the issue.

* Revert "Merge pull request #628 from apple/result_builder_changes_workaround"

This reverts commit 7e059b7, reversing
changes made to 3ca8b13.

* Use `some` syntax in variadics

This supports a type checker fix after the change in how result
builder closure parameters are type-checked.

* Type checker workaround: adjust test

* Further refactor to work around type checker regression

* Align availability macro with OS versions (#641)

* Speed up general character class matching (#642)

Short-circuit Character.isASCII checks inside built in character class matching.

Also, make benchmark try a few more times before giving up.

* Test for \s matching CRLF when scalar matching (#648)

* General ascii fast paths for character classes (#644)

General ASCII fast-paths for builtin character classes

* Remove the unsupported `anyScalar` case (#650)

We decided not to support the `anyScalar` character class, which would
match a single Unicode scalar regardless of matching mode. However,
its representation was still included in the various character class
types in the regex engine, leading to unreachable code and unclear
requirements when changing or adding new code. This change removes
that representation where possible.

The `DSLTree.Atom.CharacterClass` enum is left unchanged, since it
is marked `@_spi(RegexBuilder) public`. Any use of that enum case
is handled with a `fatalError("Unsupported")`, and it isn't produced
on any code path.

* Fix range-based quantification fast path (#653)

The fast path for quantification incorrectly discards the last save
position when the quantification used up all possible trips, which is
only possible with range-based quantifications (e.g. `{0,3}`). This
bug shows up when a range-based quantifier matches the maximum - 1
repetitions of the preceding pattern.

For example, the regex `/a{0,2}a/` should succeed as a full match any
of the strings "aa", "aaa", or "aaaa". However, the pattern fails
to match "aaa", since the save point allowing a single "a" to match
the first `a{0,2}` part of the regex is discarded.

This change only discards the last save position when advancing the
quantifier fails due to a failure to match, not maxing out the number
of trips.

* Add in ASCII fast-path for anyNonNewline (#654)

* Avoid long expression type checks (#657)

These changes remove several seconds of type-checking time from the
RegexBuilder test cases, bringing all expressions under 150ms (on
the tested computer).

* Processor cleanup (#655)

Clean up and refactor the processor

* Simplify instruction fetching

* Refactor metrics out, and void their storage in release builds

*Put operations onto String

* Fix `firstRange(of:)` search (#656)

Calls to `ranges(of:)` and `firstRange(of:)` with a string parameter
actually use two different string searching algorithms. `ranges(of:)`
uses the "z-searcher" algorithm, while `firstRange(of:)` uses a
two-way search. Since it's better to align on a single path for these
searches, the z-searcher has lower requirements, and the two-way
search implementation has a correctness bug, this change removes
the two-way search algorithm and uses z-search for `firstRange(of:)`.

The correctness bug in `firstRange(of:)` appears only when searching
for the second (or later) occurrence of a substring, which you have
to be fairly deliberate about. In the example below, the substring
at offsets `7..<12` is missed:

    let text = "ADACBADADACBADACB"
    //          =====  -----=====
    let pattern = "ADACB"
    let firstRange = text.firstRange(of: pattern)!
    // firstRange ~= 0..<5
    let secondRange = text[firstRange.upperBound...].firstRange(of: pattern)!
    // secondRange ~= 12..<17

This change also removes some unrelated, unused code in Split.swift,
in addition to removing an (unused) usage of `TwoWaySearcher`.

rdar://92794248

* Bug fix and hot path for quantified `.` (#658)

Bug fix in newline hot path, and apply hot path to quantified dot

* Run scalar-semantic benchmark variants (#659)

Run scalar semantic benchmarks

* Refactor operations to be on String (#664)

Finish refactoring logic onto String

* Provide unique generic method parameter names (#669)

This is getting warned on in the 5.9 compiler, will be an error
starting in Swift 6.

* Enable quantification optimizations for scalar semantics (#671)

*  Quantified scalar semantic matching

* Remove redundant test

---------

Co-authored-by: Nate Cook <natecook@apple.com>
Co-authored-by: Butta <repo@butta.fastem.com>
Co-authored-by: Ole Begemann <ole@oleb.net>
Co-authored-by: Alex Martini <amartini@apple.com>
Co-authored-by: Alejandro Alonso <alejandro_alonso@apple.com>
Co-authored-by: David Ewing <dewing@apple.com>
Co-authored-by: Dave Ewing <96321608+DaveEwing@users.noreply.github.com>

When a regex is anchored to the start of a subject, there's no need
to search throughout a string for the pattern when searching for the
first match: a prefix match is sufficient.

This adds a regex compilation-time check about whether a match can
only be found at the start of a subject, and then uses that to
choose whether to defer to `prefixMatch` from within `firstMatch`.

* Handle boundaries when matching in substrings (#675)

* Handle boundaries when matching in substrings

Some of our existing matching routines use the start/endIndex
of the input, which is basically never the right thing to do.

This change revises those checks to use the search bounds, by
either moving the boundary check out of the matching method, or
if the boundary is a part of what needs to be matched (e.g.
word boundaries have different behavior at the start/end than
in the middle of a string) the search bounds are passed into
the matching method.

Testing is currently handled by piggy-backing on the existing
match tests; we should add more tests to handle substring-
specific edge cases.

* Handle sub-character substring boundaries

This change passes the end boundary down into matching methods, and
uses it to find the actual character that is part of the input
substring, even if the substring's end boundary is in the middle of
a grapheme cluster.

Substrings cannot have sub-Unicode scalar boundaries as of Swift
5.7; we can remove a check for this when matching an individual
scalar.

* Add test for substring replacement

NSRegularExpression matches at the Unicode scalar level, but also
matches `\r\n` sequences with a single `.` when single-line mode is
enabled. This adds a `_nsreCompatibility` property that enables both
of those behaviors, and implements support for the special case
handling of `.`.