RegexDocumentHighlighter.GetReferences throws when editing regex inside a raw string

[vsfeedback]

This issue has been moved from a ticket on Developer Community.

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[severity:It bothers me. A fix would be nice]
I'm running into this repeatedly when editing a regex within a multiline raw string. Seems to repro consistently when I place the caret at the start of a line within the string (e.g. before the `(?[^:]+)? # Header name. Optional in case it's missing (e.g. if deleted and line starts with :Value)
(?:)? # Colon separator. No whitespace is allowed between name and colon.
([\s]*) # Whitespace is allowed after the colon before the value
(?.+)?
""", RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace);

Log message:

StreamJsonRpc.RemoteInvocationException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at StreamJsonRpc.JsonRpc.d__1451.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.CodeAnalysis.Remote.BrokeredServiceConnection1.d__181.MoveNext() RPC server exception: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index at Microsoft.CodeAnalysis.Collections.Internal.ThrowHelper.ThrowArgumentOutOfRange_IndexException() at Microsoft.CodeAnalysis.Collections.SegmentedList1.get_Item(Int32 index)
at Microsoft.CodeAnalysis.EmbeddedLanguages.VirtualChars.VirtualCharSequence.ImmutableSegmentedListChunk.Find(Int32 position)
at Microsoft.CodeAnalysis.Features.EmbeddedLanguages.RegularExpressions.LanguageServices.RegexDocumentHighlighter.GetReferences(RegexTree tree, Int32 position)
at Microsoft.CodeAnalysis.Features.EmbeddedLanguages.RegularExpressions.LanguageServices.RegexDocumentHighlighter.GetHighlights(RegexTree tree, Int32 positionInDocument)
at Microsoft.CodeAnalysis.Features.EmbeddedLanguages.RegularExpressions.LanguageServices.RegexDocumentHighlighter.GetDocumentHighlights(Document document, SemanticModel semanticModel, SyntaxToken token, Int32 position, HighlightingOptions options, CancellationToken cancellationToken)
at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.TryGetEmbeddedLanguageHighlights(Document document, SemanticModel semanticModel, Int32 position, HighlightingOptions options, CancellationToken cancellationToken)
at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.CodeAnalysis.DocumentHighlighting.AbstractDocumentHighlightsService.d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.CodeAnalysis.Remote.RemoteDocumentHighlightsService.<>c__DisplayClass2_0.<b__0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.<>c__DisplayClass7_01.<g__ProcessSolutionAsync|1>d.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.d__71.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.CodeAnalysis.Remote.RemoteWorkspace.d__71.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.d__111.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.CodeAnalysis.Remote.BrokeredServiceBase.d__14`1.MoveNext()

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### Original Comments

#### Feedback Bot on 12/6/2022, 07:01 PM: 

(private comment, text removed)
#### Feedback Bot on 12/7/2022, 07:33 AM: 

(private comment, text removed)
#### Feedback Bot on 12/7/2022, 07:33 AM: 

(private comment, text removed)

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### Original Solutions
(no solutions)

[CyrusNajmabadi]

Code is:

    private static readonly Regex s_regexHeader = new("""
        ^(?<name>[^:]+)? # Header name.  Optional in case it's missing (e.g. if deleted and line starts with :Value)
        (?<operator>:)?  # Colon separator.  No whitespace is allowed between name and colon.
        ([\s]*)          # Whitespace is allowed after the colon before the value
        (?<value>.+)?    
        """, RegexOptions.Compiled | RegexOptions.IgnorePatternWhitespace);

[CyrusNajmabadi]

Repros for me. Investigating.