dotnet/roslyn

VB parsing string-interpolation in erroneous code has poor error recovery

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#3,617 opened on Jun 22, 2015

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Area-CompilersBugConcept-Diagnostic Clarityhelp wanted

Description

Watch this video: string-interpolation-parsing

I get into this situation often when I'm copying+pasting code around, or breaking a method up into smaller methods by deleting "sub" and then re-adding a bunch of "sub" and "end sub" statements where appropriate.

WHAT I OBSERVE: When there's a valid statement, regular strings and interpolated string parse fine.

When there's an invalid statement, regular strings parse fine, but interpolated strings don't recognize their terminating quote, so the remainder of the entire file gets "stringed out".

WHAT I EXPECT: interpolated strings should believe themselves terminated at the terminating quote, just like regular strings do.

Contributor guide

Tech stack
csharp
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Visual Basic syntaxcompiler parsing basicserror recovery conceptsRoslyn VB parser code
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Investigate the VB parser's handling of string interpolation in error recovery. Look at the relevant parsing code in the VB syntax parser, likely in files such as 'VbParse.vb' or 'SyntaxParser.vb'. The issue is that interpolated strings do not terminate on the closing quote when there is a prior syntax error. Examine the existing error recovery logic for regular strings versus interpolated strings and propose a fix that ensures the terminating quote is recognized even in error scenarios.