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Surprising precedence when stringifying concatenations of alternations #516

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exists-forall opened this issue Sep 18, 2018 · 3 comments
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@exists-forall
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exists-forall commented Sep 18, 2018

In the hir module of the regex-syntax crate, concatenating onto an alternation and calling to_string on the resulting concatenation currently produces a pattern string where the concatenation binds more tightly than the alternation. This is most easily understood with an example: https://play.rust-lang.org/?gist=36767c381c97f169e219c8c707c001ad&version=stable&mode=debug&edition=2015

I don't know if this current behavior is intended or not, but I originally expected that the pattern string printed in the example above would look something like A(?:B|C), not AB|C, as the concatenation is logically the root of the HIR tree. Would it be possible to at least document this behavior?

@BurntSushi
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Hmm, yeah, I agree, that does not look right to me. Looking at the HIR, this looks like it might be a bug in the printer because the HIR looks right to me: https://play.rust-lang.org/?gist=cea5cb88a7985fc36a94e73bcc221c7a&version=stable&mode=debug&edition=2015

It seems plausible that the printer is probably resisting putting a non-capturing group into the concrete syntax that does not itself exist in the HIR. So the question here is whether the HIR construction should be updated to insert a group itself or if the printer should recognize that Hir::Something followed by a Hir::Alternation requires a non-capturing group.

When faced with these decisions, I think I've generally leaned towards fixing this at construction time, such that certain combinations of HIR are never possible. For example, it should be impossible to get a Concat(Expr) since it is always equivalent to just Expr.

@BurntSushi BurntSushi added the bug label Sep 18, 2018
@ethanpailes
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ethanpailes commented Sep 18, 2018 via email

@BurntSushi
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I have a fix incoming that will land as part of the #656 work. Here's the commit message that explains everything and my fix. TL;DR - I tweaked the printer.

syntax: fix HIR printer

This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731

BurntSushi added a commit that referenced this issue Sep 20, 2022
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Sep 25, 2022
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Nov 5, 2022
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Jan 6, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Jan 13, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Mar 2, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Mar 4, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Mar 5, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Mar 15, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Mar 21, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Apr 15, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Apr 17, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Apr 17, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Apr 17, 2023
This fixes some corner cases in the HIR printer where it would print the
concrete syntax of a regex that does not match the natural
interpretation of the HIR. One such example of this is:

    concat(a, alt(b, c))

This would get printed as

    ab|c

But clearly, it should be printed as:

    a(?:b|c)

The issue here is that the printer only considers the current HirKind
when determining how to print it. Sometimes a group is needed to print
an alt (and even a concat, in the case of 'rep(+, concat(a, b))'), but
sometimes it isn't.

We could address this in a few different ways:

1) Always print concats and alts inside a non-capturing group.
2) Make the printer detect precisely the cases where a non-capturing
   group is needed.
3) Make the HIR smart constructors insert non-capturing groups when
   needed.
4) Do some other thing to change the HIR to prevent these sorts of
   things by construction.

This patch goes with (1). The reason in favor of it is that HIR printer
was always about printing an equivalent regex and never about trying to
print a "nice" regex. Indeed, the HIR printer can't print a nice regex,
because the HIR represents a rigorously simplifed view of a regex to
make analysis easier. (The most obvious such example are Unicode
character classes. For example, the HIR printer never prints '\w'.) So
inserting some extra groups (which it already does) even when they
aren't strictly needed is perfectly okay.

But still, it's useful to say why we didn't do the other choices:

2) Modifying the printer to only print groups when they're actually
   needed is pretty difficult. I tried this briefly, and handling this
   case requires some notion of what the parent expression is. This
   winds up being a possible but hairy change.
3) Making the HIR more complicated to make the printer correct seems
   like it's optimizing for the wrong thing. Inserting extra groups in
   places just obfuscates HIR values that already have clear semantics.
   That is, use concat(a, alt(b, c)) over concat(a, group(alt(b, c))).
4) It's not clear how we would change the HIR to guarantee this sort of
   thing wouldn't happen. At the very least, it seems likely it would
   require a more complex data type.

At first, I had thought (1) seemed inelegant. But the more I thought
about it, the more it seemed quite consistent with how the HIR printer
already worked. So that's the path I took here.

Closes #516, Closes #731
BurntSushi added a commit that referenced this issue Apr 20, 2023
1.8.0 (2023-04-20)
==================
This is a sizeable release that will be soon followed by another sizeable
release. Both of them will combined close over 40 existing issues and PRs.

This first release, despite its size, essentially represent preparatory work
for the second release, which will be even bigger. Namely, this release:

* Increases the MSRV to Rust 1.60.0, which was released about 1 year ago.
* Upgrades its dependency on `aho-corasick` to the recently release 1.0
version.
* Upgrades its dependency on `regex-syntax` to the simultaneously released
`0.7` version. The changes to `regex-syntax` principally revolve around a
rewrite of its literal extraction code and a number of simplifications and
optimizations to its high-level intermediate representation (HIR).

The second release, which will follow ~shortly after the release above, will
contain a soup-to-nuts rewrite of every regex engine. This will be done by
bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into
this repository, and then changing the `regex` crate to be nothing but an API
shim layer on top of `regex-automata`'s API.

These tandem releases are the culmination of about 3
years of on-and-off work that [began in earnest in March
2020](#656).

Because of the scale of changes involved in these releases, I would love to
hear about your experience. Especially if you notice undocumented changes in
behavior or performance changes (positive *or* negative).

Most changes in the first release are listed below. For more details, please
see the commit log, which reflects a linear and decently documented history
of all changes.

New features:

* [FEATURE #501](#501):
Permit many more characters to be escaped, even if they have no significance.
More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be
escaped. Also, a new routine, `is_escapeable_character`, has been added to
`regex-syntax` to query whether a character is escapeable or not.
* [FEATURE #547](#547):
Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise
introduce any new expressive power.
* [FEATURE #595](#595):
Capture group names are now Unicode-aware. They can now begin with either a `_`
or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints
can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and
`]`. Note that replacement syntax has not changed.
* [FEATURE #810](#810):
Add `Match::is_empty` and `Match::len` APIs.
* [FEATURE #905](#905):
Add an `impl Default for RegexSet`, with the default being the empty set.
* [FEATURE #908](#908):
A new method, `Regex::static_captures_len`, has been added which returns the
number of capture groups in the pattern if and only if every possible match
always contains the same number of matching groups.
* [FEATURE #955](#955):
Named captures can now be written as `(?<name>re)` in addition to
`(?P<name>re)`.
* FEATURE: `regex-syntax` now supports empty character classes.
* FEATURE: `regex-syntax` now has an optional `std` feature. (This will come
to `regex` in the second release.)
* FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications
made to it.
* FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF
mode. This will be supported in `regex` proper in the second release.
* FEATURE: `regex-syntax` now has proper support for "regex that never
matches" via `Hir::fail()`.
* FEATURE: The `hir::literal` module of `regex-syntax` has been completely
re-worked. It now has more documentation, examples and advice.
* FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed
to `utf8`, and the meaning of the boolean has been flipped.

Performance improvements:

* PERF: The upgrade to `aho-corasick 1.0` may improve performance in some
cases. It's difficult to characterize exactly which patterns this might impact,
but if there are a small number of longish (>= 4 bytes) prefix literals, then
it might be faster than before.

Bug fixes:

* [BUG #514](#514):
Improve `Debug` impl for `Match` so that it doesn't show the entire haystack.
* BUGS [#516](#516),
[#731](#731):
Fix a number of issues with printing `Hir` values as regex patterns.
* [BUG #610](#610):
Add explicit example of `foo|bar` in the regex syntax docs.
* [BUG #625](#625):
Clarify that `SetMatches::len` does not (regretably) refer to the number of
matches in the set.
* [BUG #660](#660):
Clarify "verbose mode" in regex syntax documentation.
* BUG [#738](#738),
[#950](#950):
Fix `CaptureLocations::get` so that it never panics.
* [BUG #747](#747):
Clarify documentation for `Regex::shortest_match`.
* [BUG #835](#835):
Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`.
* [BUG #846](#846):
Add more clarifying documentation to the `CompiledTooBig` error variant.
* [BUG #854](#854):
Clarify that `regex::Regex` searches as if the haystack is a sequence of
Unicode scalar values.
* [BUG #884](#884):
Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute.
* [BUG #893](#893):
Optimize case folding since it can get quite slow in some pathological cases.
* [BUG #895](#895):
Reject `(?-u:\W)` in `regex::Regex` APIs.
* [BUG #942](#942):
Add a missing `void` keyword to indicate "no parameters" in C API.
* [BUG #965](#965):
Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`.
* [BUG #975](#975):
Clarify documentation for `\pX` syntax.
BurntSushi added a commit that referenced this issue Apr 20, 2023
1.8.0 (2023-04-20)
==================
This is a sizeable release that will be soon followed by another sizeable
release. Both of them will combined close over 40 existing issues and PRs.

This first release, despite its size, essentially represent preparatory work
for the second release, which will be even bigger. Namely, this release:

* Increases the MSRV to Rust 1.60.0, which was released about 1 year ago.
* Upgrades its dependency on `aho-corasick` to the recently release 1.0
version.
* Upgrades its dependency on `regex-syntax` to the simultaneously released
`0.7` version. The changes to `regex-syntax` principally revolve around a
rewrite of its literal extraction code and a number of simplifications and
optimizations to its high-level intermediate representation (HIR).

The second release, which will follow ~shortly after the release above, will
contain a soup-to-nuts rewrite of every regex engine. This will be done by
bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into
this repository, and then changing the `regex` crate to be nothing but an API
shim layer on top of `regex-automata`'s API.

These tandem releases are the culmination of about 3
years of on-and-off work that [began in earnest in March
2020](#656).

Because of the scale of changes involved in these releases, I would love to
hear about your experience. Especially if you notice undocumented changes in
behavior or performance changes (positive *or* negative).

Most changes in the first release are listed below. For more details, please
see the commit log, which reflects a linear and decently documented history
of all changes.

New features:

* [FEATURE #501](#501):
Permit many more characters to be escaped, even if they have no significance.
More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be
escaped. Also, a new routine, `is_escapeable_character`, has been added to
`regex-syntax` to query whether a character is escapeable or not.
* [FEATURE #547](#547):
Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise
introduce any new expressive power.
* [FEATURE #595](#595):
Capture group names are now Unicode-aware. They can now begin with either a `_`
or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints
can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and
`]`. Note that replacement syntax has not changed.
* [FEATURE #810](#810):
Add `Match::is_empty` and `Match::len` APIs.
* [FEATURE #905](#905):
Add an `impl Default for RegexSet`, with the default being the empty set.
* [FEATURE #908](#908):
A new method, `Regex::static_captures_len`, has been added which returns the
number of capture groups in the pattern if and only if every possible match
always contains the same number of matching groups.
* [FEATURE #955](#955):
Named captures can now be written as `(?<name>re)` in addition to
`(?P<name>re)`.
* FEATURE: `regex-syntax` now supports empty character classes.
* FEATURE: `regex-syntax` now has an optional `std` feature. (This will come
to `regex` in the second release.)
* FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications
made to it.
* FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF
mode. This will be supported in `regex` proper in the second release.
* FEATURE: `regex-syntax` now has proper support for "regex that never
matches" via `Hir::fail()`.
* FEATURE: The `hir::literal` module of `regex-syntax` has been completely
re-worked. It now has more documentation, examples and advice.
* FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed
to `utf8`, and the meaning of the boolean has been flipped.

Performance improvements:

* PERF: The upgrade to `aho-corasick 1.0` may improve performance in some
cases. It's difficult to characterize exactly which patterns this might impact,
but if there are a small number of longish (>= 4 bytes) prefix literals, then
it might be faster than before.

Bug fixes:

* [BUG #514](#514):
Improve `Debug` impl for `Match` so that it doesn't show the entire haystack.
* BUGS [#516](#516),
[#731](#731):
Fix a number of issues with printing `Hir` values as regex patterns.
* [BUG #610](#610):
Add explicit example of `foo|bar` in the regex syntax docs.
* [BUG #625](#625):
Clarify that `SetMatches::len` does not (regretably) refer to the number of
matches in the set.
* [BUG #660](#660):
Clarify "verbose mode" in regex syntax documentation.
* BUG [#738](#738),
[#950](#950):
Fix `CaptureLocations::get` so that it never panics.
* [BUG #747](#747):
Clarify documentation for `Regex::shortest_match`.
* [BUG #835](#835):
Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`.
* [BUG #846](#846):
Add more clarifying documentation to the `CompiledTooBig` error variant.
* [BUG #854](#854):
Clarify that `regex::Regex` searches as if the haystack is a sequence of
Unicode scalar values.
* [BUG #884](#884):
Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute.
* [BUG #893](#893):
Optimize case folding since it can get quite slow in some pathological cases.
* [BUG #895](#895):
Reject `(?-u:\W)` in `regex::Regex` APIs.
* [BUG #942](#942):
Add a missing `void` keyword to indicate "no parameters" in C API.
* [BUG #965](#965):
Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`.
* [BUG #975](#975):
Clarify documentation for `\pX` syntax.
crapStone added a commit to Calciumdibromid/CaBr2 that referenced this issue May 2, 2023
This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [regex](https://github.com/rust-lang/regex) | dependencies | minor | `1.7.3` -> `1.8.1` |

---

### Release Notes

<details>
<summary>rust-lang/regex</summary>

### [`v1.8.1`](https://github.com/rust-lang/regex/blob/HEAD/CHANGELOG.md#&#8203;181-2023-04-21)

\==================
This is a patch release that fixes a bug where a regex match could be reported
where none was found. Specifically, the bug occurs when a pattern contains some
literal prefixes that could be extracted *and* an optional word boundary in the
prefix.

Bug fixes:

-   [BUG #&#8203;981](rust-lang/regex#981):
    Fix a bug where a word boundary could interact with prefix literal
    optimizations and lead to a false positive match.

### [`v1.8.0`](https://github.com/rust-lang/regex/blob/HEAD/CHANGELOG.md#&#8203;180-2023-04-20)

\==================
This is a sizeable release that will be soon followed by another sizeable
release. Both of them will combined close over 40 existing issues and PRs.

This first release, despite its size, essentially represents preparatory work
for the second release, which will be even bigger. Namely, this release:

-   Increases the MSRV to Rust 1.60.0, which was released about 1 year ago.
-   Upgrades its dependency on `aho-corasick` to the recently released 1.0
    version.
-   Upgrades its dependency on `regex-syntax` to the simultaneously released
    `0.7` version. The changes to `regex-syntax` principally revolve around a
    rewrite of its literal extraction code and a number of simplifications and
    optimizations to its high-level intermediate representation (HIR).

The second release, which will follow ~shortly after the release above, will
contain a soup-to-nuts rewrite of every regex engine. This will be done by
bringing [`regex-automata`](https://github.com/BurntSushi/regex-automata) into
this repository, and then changing the `regex` crate to be nothing but an API
shim layer on top of `regex-automata`'s API.

These tandem releases are the culmination of about 3
years of on-and-off work that [began in earnest in March
2020](rust-lang/regex#656).

Because of the scale of changes involved in these releases, I would love to
hear about your experience. Especially if you notice undocumented changes in
behavior or performance changes (positive *or* negative).

Most changes in the first release are listed below. For more details, please
see the commit log, which reflects a linear and decently documented history
of all changes.

New features:

-   [FEATURE #&#8203;501](rust-lang/regex#501):
    Permit many more characters to be escaped, even if they have no significance.
    More specifically, any ASCII character except for `[0-9A-Za-z<>]` can now be
    escaped. Also, a new routine, `is_escapeable_character`, has been added to
    `regex-syntax` to query whether a character is escapeable or not.
-   [FEATURE #&#8203;547](rust-lang/regex#547):
    Add `Regex::captures_at`. This filles a hole in the API, but doesn't otherwise
    introduce any new expressive power.
-   [FEATURE #&#8203;595](rust-lang/regex#595):
    Capture group names are now Unicode-aware. They can now begin with either a `_`
    or any "alphabetic" codepoint. After the first codepoint, subsequent codepoints
    can be any sequence of alpha-numeric codepoints, along with `_`, `.`, `[` and
    `]`. Note that replacement syntax has not changed.
-   [FEATURE #&#8203;810](rust-lang/regex#810):
    Add `Match::is_empty` and `Match::len` APIs.
-   [FEATURE #&#8203;905](rust-lang/regex#905):
    Add an `impl Default for RegexSet`, with the default being the empty set.
-   [FEATURE #&#8203;908](rust-lang/regex#908):
    A new method, `Regex::static_captures_len`, has been added which returns the
    number of capture groups in the pattern if and only if every possible match
    always contains the same number of matching groups.
-   [FEATURE #&#8203;955](rust-lang/regex#955):
    Named captures can now be written as `(?<name>re)` in addition to
    `(?P<name>re)`.
-   FEATURE: `regex-syntax` now supports empty character classes.
-   FEATURE: `regex-syntax` now has an optional `std` feature. (This will come
    to `regex` in the second release.)
-   FEATURE: The `Hir` type in `regex-syntax` has had a number of simplifications
    made to it.
-   FEATURE: `regex-syntax` has support for a new `R` flag for enabling CRLF
    mode. This will be supported in `regex` proper in the second release.
-   FEATURE: `regex-syntax` now has proper support for "regex that never
    matches" via `Hir::fail()`.
-   FEATURE: The `hir::literal` module of `regex-syntax` has been completely
    re-worked. It now has more documentation, examples and advice.
-   FEATURE: The `allow_invalid_utf8` option in `regex-syntax` has been renamed
    to `utf8`, and the meaning of the boolean has been flipped.

Performance improvements:

-   PERF: The upgrade to `aho-corasick 1.0` may improve performance in some
    cases. It's difficult to characterize exactly which patterns this might impact,
    but if there are a small number of longish (>= 4 bytes) prefix literals, then
    it might be faster than before.

Bug fixes:

-   [BUG #&#8203;514](rust-lang/regex#514):
    Improve `Debug` impl for `Match` so that it doesn't show the entire haystack.
-   BUGS [#&#8203;516](rust-lang/regex#516),
    [#&#8203;731](rust-lang/regex#731):
    Fix a number of issues with printing `Hir` values as regex patterns.
-   [BUG #&#8203;610](rust-lang/regex#610):
    Add explicit example of `foo|bar` in the regex syntax docs.
-   [BUG #&#8203;625](rust-lang/regex#625):
    Clarify that `SetMatches::len` does not (regretably) refer to the number of
    matches in the set.
-   [BUG #&#8203;660](rust-lang/regex#660):
    Clarify "verbose mode" in regex syntax documentation.
-   BUG [#&#8203;738](rust-lang/regex#738),
    [#&#8203;950](rust-lang/regex#950):
    Fix `CaptureLocations::get` so that it never panics.
-   [BUG #&#8203;747](rust-lang/regex#747):
    Clarify documentation for `Regex::shortest_match`.
-   [BUG #&#8203;835](rust-lang/regex#835):
    Fix `\p{Sc}` so that it is equivalent to `\p{Currency_Symbol}`.
-   [BUG #&#8203;846](rust-lang/regex#846):
    Add more clarifying documentation to the `CompiledTooBig` error variant.
-   [BUG #&#8203;854](rust-lang/regex#854):
    Clarify that `regex::Regex` searches as if the haystack is a sequence of
    Unicode scalar values.
-   [BUG #&#8203;884](rust-lang/regex#884):
    Replace `__Nonexhaustive` variants with `#[non_exhaustive]` attribute.
-   [BUG #&#8203;893](rust-lang/regex#893):
    Optimize case folding since it can get quite slow in some pathological cases.
-   [BUG #&#8203;895](rust-lang/regex#895):
    Reject `(?-u:\W)` in `regex::Regex` APIs.
-   [BUG #&#8203;942](rust-lang/regex#942):
    Add a missing `void` keyword to indicate "no parameters" in C API.
-   [BUG #&#8203;965](rust-lang/regex#965):
    Fix `\p{Lc}` so that it is equivalent to `\p{Cased_Letter}`.
-   [BUG #&#8203;975](rust-lang/regex#975):
    Clarify documentation for `\pX` syntax.

</details>

---

### Configuration

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---

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---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
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Co-authored-by: cabr2-bot <cabr2.help@gmail.com>
Co-authored-by: crapStone <crapstone01@gmail.com>
Reviewed-on: https://codeberg.org/Calciumdibromid/CaBr2/pulls/1874
Reviewed-by: crapStone <crapstone@noreply.codeberg.org>
Co-authored-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
Co-committed-by: Calciumdibromid Bot <cabr2_bot@noreply.codeberg.org>
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