api: add TryFrom impls for Regex

This enables builder APIs to take `T: TryInto<Regex>`, where `T` can be
a string or a preconstructed `Regex` instance.

Closes #1022

CHANGELOG.md

@@ -40,6 +40,8 @@ Anchored search APIs are now available in `regex-automata 0.3`.
 Add new `Captures::extract` method for easier capture group access.
 * [FEATURE #961](https://github.com/rust-lang/regex/issues/961):
 Add `regex-lite` crate with smaller binary sizes and faster compile times.
+* [FEATURE #1022](https://github.com/rust-lang/regex/pull/1022):
+Add `TryFrom` implementations for the `Regex` type.
 
 Performance improvements:
 

regex-lite/src/string.rs

@@ -117,6 +117,24 @@ impl core::str::FromStr for Regex {
     }
 }
 
+impl TryFrom<&str> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: &str) -> Result<Regex, Error> {
+        Regex::new(s)
+    }
+}
+
+impl TryFrom<String> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: String) -> Result<Regex, Error> {
+        Regex::new(&s)
+    }
+}
+
 /// Core regular expression methods.
 impl Regex {
     /// Compiles a regular expression. Once compiled, it can be used repeatedly

src/regex/bytes.rs

@@ -1,4 +1,4 @@
-use alloc::{borrow::Cow, sync::Arc, vec::Vec};
+use alloc::{borrow::Cow, string::String, sync::Arc, vec::Vec};
 
 use regex_automata::{meta, util::captures, Input, PatternID};
 
@@ -124,6 +124,24 @@ impl core::str::FromStr for Regex {
     }
 }
 
+impl TryFrom<&str> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: &str) -> Result<Regex, Error> {
+        Regex::new(s)
+    }
+}
+
+impl TryFrom<String> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: String) -> Result<Regex, Error> {
+        Regex::new(&s)
+    }
+}
+
 /// Core regular expression methods.
 impl Regex {
     /// Compiles a regular expression. Once compiled, it can be used repeatedly

src/regex/string.rs

@@ -126,6 +126,24 @@ impl core::str::FromStr for Regex {
     }
 }
 
+impl TryFrom<&str> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: &str) -> Result<Regex, Error> {
+        Regex::new(s)
+    }
+}
+
+impl TryFrom<String> for Regex {
+    type Error = Error;
+
+    /// Attempts to parse a string into a regular expression
+    fn try_from(s: String) -> Result<Regex, Error> {
+        Regex::new(&s)
+    }
+}
+
 /// Core regular expression methods.
 impl Regex {
     /// Compiles a regular expression. Once compiled, it can be used repeatedly