F#: Improved character literals (#1956)

This adds support for all F# character escapes which should result in all characters being highlighted as such. 
The problem was that character literals with escape sequences longer than two characters were not recognized.

components/prism-fsharp.js

@@ -10,7 +10,7 @@ Prism.languages.fsharp = Prism.languages.extend('clike', {
 		}
 	],
 	'string': {
-		pattern: /(?:"""[\s\S]*?"""|@"(?:""|[^"])*"|"(?:\\[\s\S]|[^\\"])*")B?|'(?:[^\\']|\\.)'B?/,
+		pattern: /(?:"""[\s\S]*?"""|@"(?:""|[^"])*"|"(?:\\[\s\S]|[^\\"])*")B?|'(?:[^\\']|\\(?:.|\d{3}|x[a-fA-F\d]{2}|u[a-fA-F\d]{4}|U[a-fA-F\d]{8}))'B?/,
 		greedy: true
 	},
 	'class-name': {

examples/prism-fsharp.html

@@ -5,7 +5,6 @@ <h2>Comments</h2>
 
 <h2>Strings</h2>
 <pre><code>"foo \"bar\" baz"
-'foo \'bar\' baz'
 @"Verbatim strings"
 """Alternate "verbatim" strings"""
 </code></pre>
@@ -58,32 +57,32 @@ <h2>Numbers</h2>
 </code></pre>
 
 <h2>Full example</h2>
-<pre><code>// The declaration creates a constructor that takes two values, name and age. 
+<pre><code>// The declaration creates a constructor that takes two values, name and age.
 type Person(name:string, age:int) =
-    // A Person object's age can be changed. The mutable keyword in the 
-    // declaration makes that possible. 
+    // A Person object's age can be changed. The mutable keyword in the
+    // declaration makes that possible.
     let mutable internalAge = age
 
-    // Declare a second constructor that takes only one argument, a name. 
-    // This constructor calls the constructor that requires two arguments, 
-    // sending 0 as the value for age. 
+    // Declare a second constructor that takes only one argument, a name.
+    // This constructor calls the constructor that requires two arguments,
+    // sending 0 as the value for age.
     new(name:string) = Person(name, 0)
 
-    // A read-only property. 
+    // A read-only property.
     member this.Name = name
-    // A read/write property. 
+    // A read/write property.
     member this.Age
         with get() = internalAge
         and set(value) = internalAge &lt;- value
 
-    // Instance methods. 
-    // Increment the person's age. 
+    // Instance methods.
+    // Increment the person's age.
     member this.HasABirthday () = internalAge &lt;- internalAge + 1
 
-    // Check current age against some threshold. 
+    // Check current age against some threshold.
     member this.IsOfAge targetAge = internalAge &gt;= targetAge
 
-    // Display the person's name and age. 
-    override this.ToString () = 
+    // Display the person's name and age.
+    override this.ToString () =
         "Name:  " + name + "\n" + "Age:   " + (string)internalAge
-</code></pre>
+</code></pre>

tests/languages/fsharp/string_feature.test

@@ -18,6 +18,10 @@ bar"""
 'a'B
 '\''
 '\\'
+'\231'
+'\x41'
+'\u0041'
+'\U0001F47D'
 
 ----------------------------------------------------
 
@@ -39,9 +43,13 @@ bar"""
 	["string", "'a'"],
 	["string", "'a'B"],
 	["string", "'\\''"],
-	["string", "'\\\\'"]
+	["string", "'\\\\'"],
+	["string", "'\\231'"],
+	["string", "'\\x41'"],
+	["string", "'\\u0041'"],
+	["string", "'\\U0001F47D'"]
 ]
 
 ----------------------------------------------------
 
-Checks for normal strings, verbatim strings, triple-quoted strings and character literals.
+Checks for normal strings, verbatim strings, triple-quoted strings and character literals.