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impl Default for RegexSet? #905

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sourcefrog opened this issue Sep 21, 2022 · 3 comments
Closed

impl Default for RegexSet? #905

sourcefrog opened this issue Sep 21, 2022 · 3 comments

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@sourcefrog
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Describe your feature request

Would it be reasonable to impl Default on RegexSet, returning an empty set as if it was constructed from an empty list?

This would be helpful when using it inside a struct for which I want to derive Default.

sourcefrog added a commit to sourcefrog/regex that referenced this issue Sep 21, 2022
@BurntSushi
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The question that immediately comes to mind here is, "why does RegexSet have a Default impl, but Regex does not?"

I guess the answer to that is that a set has a natural default value: the empty set. And an empty set never matches anything. But I would suppose a Regex could also have a default value, either perhaps the empty string (matches everywhere) or even a regex that itself never matches (i.e., an empty character class).

@BurntSushi
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I think it just feels weird to me to construct an empty RegexSet just because it's convenient. Why not use an Option<RegexSet> instead?

@sourcefrog
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sourcefrog commented Sep 22, 2022

My current code does in fact use an Option<RegexSet>, but it just feels a bit repetitive to say "is there a RegexSet and if so is it not empty?"

Or in fact it introduces a risk of different behavior when it is None vs Some(RegexSet::empty()), which I'd rather avoid. You could say, well, that's my problem to avoid. But it seems idiomatic in Rust to have an impl Default for everything that has a clearly-defined empty value?

        if let Some(examine_re) = &options.examine_functions {
            if !examine_re.is_empty() {
                mutants.retain(|m| examine_re.is_match(&m.format_as_error_message()));
            }
        }
        if let Some(exclude_re) = &options.exclude_functions {
            if !exclude_re.is_empty() {
                mutants.retain(|m| !exclude_re.is_match(&m.format_as_error_message()));
            }
        }

I had the same thoughts about whether there should be a default Regex and whether it should match everything or nothing, which gets a bit philosophical.

But for RegexSet it seems much easier, because as you say

  1. It is the same thing you get from passing a default vec or other iterable to the new constructor, i.e. empty.
  2. It already has a well-defined concept of being empty, literally under that name.
  3. It's described as a set and as a union of regexes and those all have an obvious zero identity, i.e. empty, without having to define a default for Regex.

(I think on the whole perhaps Regex::default could be the same as a regex compiled from "", i.e. a zero-length match. But we don't need to get into that here, and it does seem like a less safe default.)

BurntSushi pushed a commit that referenced this issue Mar 4, 2023
This is justified by the fact that a RegexSet is, after all, a set. And
a set has a very obvious default value: the empty set. Plus, this is
exactly what you get by passing a default `Vec` or an empty iterator to
the `RegexSet::new` constructor.

We specifically do not add a `Default` impl for Regex because it has no
obvious default value.

Fixes #905, Closes #906
BurntSushi pushed a commit that referenced this issue Mar 21, 2023
This is justified by the fact that a RegexSet is, after all, a set. And
a set has a very obvious default value: the empty set. Plus, this is
exactly what you get by passing a default `Vec` or an empty iterator to
the `RegexSet::new` constructor.

We specifically do not add a `Default` impl for Regex because it has no
obvious default value.

Fixes #905, Closes #906
BurntSushi pushed a commit that referenced this issue Apr 15, 2023
This is justified by the fact that a RegexSet is, after all, a set. And
a set has a very obvious default value: the empty set. Plus, this is
exactly what you get by passing a default `Vec` or an empty iterator to
the `RegexSet::new` constructor.

We specifically do not add a `Default` impl for Regex because it has no
obvious default value.

Fixes #905, Closes #906
BurntSushi pushed a commit that referenced this issue Apr 17, 2023
This is justified by the fact that a RegexSet is, after all, a set. And
a set has a very obvious default value: the empty set. Plus, this is
exactly what you get by passing a default `Vec` or an empty iterator to
the `RegexSet::new` constructor.

We specifically do not add a `Default` impl for Regex because it has no
obvious default value.

Fixes #905, Closes #906
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>

---

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sourcefrog added a commit to sourcefrog/cargo-mutants that referenced this issue Nov 25, 2023
Gets Default for RegexSet from
<rust-lang/regex#905>
which should make Options a little simpler
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