Improve parser error recovery for property declarations with missing identifiers by Copilot · Pull Request #81003 · dotnet/roslyn

Copilot · 2025-11-03T21:17:34Z

Improve parser error recovery for property declarations with missing identifiers

Summary

Successfully implemented error recovery for property declarations with missing identifiers. The parser now correctly recognizes properties even when the identifier is missing, as long as the property body ({ get; set; } or =>) is present.

Plan:

Technical Implementation:

The fix adds error recovery in three key places:

IsNoneOrIncompleteMember: Checks for property body start tokens before creating an incomplete member
TryParseIndexerOrPropertyDeclaration: Synthesizes a missing identifier when we see a property body but no identifier
Debug.Assert updates: Allows null identifiers when a property body is detected

Validation:

✅ Core Fix Validated: The test PropertyWithMissingIdentifier_WithAccessors demonstrates that:

All 4 members in the test class are parsed as PropertyDeclaration (not IncompleteMember)
Only 2 targeted errors are reported (for the 2 properties with missing identifiers)
Subsequent members parse correctly (no cascading errors)

This matches the requirement from the issue: "The parser properly recovers by implying a missing identifier/type name on the property declaration."

Remaining Work:

18 existing tests need their expectations updated. These are NOT regressions - they represent IMPROVED error reporting:

Old: Generic ERR_InvalidMemberDecl errors
New: Specific ERR_IdentifierExpected errors (more helpful to users)

The changes provide better error messages that guide users more precisely to the actual problem (missing identifier) rather than a vague "invalid member declaration" message.

Original prompt

This section details on the original issue you should resolve

<issue_title>Improve error recovery on missing type or identifier for property declaration</issue_title>
<issue_description>Version Used:
VS 2022 Version 17.9.2
Roslyn 4.9.0 (a98c90d)

Steps to Reproduce:

Declare a property inside a type

Remove the type or the identifier of the property, while preserving the accessors

SharpLab repro with the below snippet: here

For now, a snippet is provided below:
public class Stuff
{
    public required string Name { get; set; }
    public required Value { get; set; }
    public string? SecondaryName { get; set; }
    public SecondaryValue { get; set; }
}
Expected Behavior:

The parser properly recovers by implying a missing identifier/type name on the property declaration.

Actual Behavior:

The rest of the file breaks and declarations are incorrectly parsed, yielding unexpected binding and tokenizing errors.
</issue_description>

<agent_instructions>@copilot we should be able to update the property parsing logic in LanguageParser to see that { get (or any of the other accessors) are present, and understand that this is a property with a missing identifier that it can recover gracefully from.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes Improve error recovery on missing type or identifier for property declaration #72354

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

…ifiers Add error recovery in TryParseIndexerOrPropertyDeclaration to handle cases where a property has a missing identifier but the accessor list or expression body is present. When we detect a property body start token ('{' or '=>') but no identifier, we synthesize a missing identifier and continue parsing as a property rather than creating an incomplete member. This improves parser recovery when users forget to add a property name, allowing the rest of the file to parse correctly instead of cascading errors. Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Update RequiredModifierProperty tests to reflect the improved error recovery. With the new parser changes, properties with missing identifiers now produce clearer ERR_IdentifierExpected errors instead of generic ERR_InvalidMemberDecl errors, which is better for users. Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Add clarifying comment to PropertyWithMissingIdentifier_WithAccessors test to highlight that the key validation is that all members were parsed as properties (not incomplete members), which confirms the error recovery is working correctly. Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

…otnet/roslyn into copilot/improve-error-recovery

src/Compilers/CSharp/Test/Syntax/Parsing/MemberDeclarationParsingTests.cs

- Add [Fact, WorkItem(...)] attributes to PropertyWithMissingIdentifier tests - Move closing parenthesis to end of last Diagnostic line for consistency Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-11-04T20:09:30Z

src/Analyzers/CSharp/Tests/UsePatternMatching/CSharpAsAndNullCheckTests_FixAllTests.cs

@@ -160,22 +160,22 @@ class Symbol

                void M(object o, bool b0, bool b1)


this test was affected because the line above is public ContainingSymbol { get; }. Instead of going off the rails, we now properly parse and recover. So formatting works properly below.

CyrusNajmabadi · 2025-11-04T20:10:10Z

@dotnet/roslyn-compiler ptal.

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

RikkiGibson · 2025-11-05T01:56:12Z

Will try to review in depth tomorrow.

Co-authored-by: Rikki Gibson <rigibson@microsoft.com>

…or-recovery

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

jjonescz · 2025-11-10T10:41:21Z

src/Compilers/CSharp/Test/Syntax/LexicalAndXml/LexicalErrorTests.cs

-                // (6,1): error CS1022: Type or namespace definition, or end-of-file expected
-                // }
-                Diagnostic(ErrorCode.ERR_EOFExpected, "}").WithLocation(6, 1));
+                Diagnostic(ErrorCode.ERR_IdentifierExpected, "").WithLocation(3, 20));


Shouldn't there be some non-empty squiggled text?

in this case, we're saying that we expect an identifier after the \e but before the {. Since it's a missing token, and we're at the end of a line, we just identify the position. The host will squiggle something in this event, but this is the expected way for the diagnostic itself to work.

src/Compilers/CSharp/Test/Syntax/Parsing/DeclarationParsingTests.cs

Co-authored-by: Jan Jones <janjones@microsoft.com>

…or-recovery

CyrusNajmabadi · 2025-11-11T21:57:53Z

@RikkiGibson ptal

RikkiGibson · 2025-11-12T00:21:57Z

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

+            out MemberDeclarationSyntax result)
        {
-            if (identifierOrThisOpt.Kind == SyntaxKind.ThisKeyword)
+            if (identifierOrThisOpt?.Kind == SyntaxKind.ThisKeyword)


note to self: check what the parse is for public int [int index] { get; set; }

.NET Lab

It's a decent chunk of stuff

Cannot execute due to compilation errors: /Program.cs(17,26): error CS1525: Invalid expression term 'int' /Program.cs(17,30): error CS1003: Syntax error, ',' expected /Program.cs(17,37): error CS1519: Invalid token '{' in a member declaration /Program.cs(17,42): error CS1519: Invalid token ';' in a member declaration /Program.cs(17,42): error CS1519: Invalid token ';' in a member declaration /Program.cs(17,47): error CS1519: Invalid token ';' in a member declaration /Program.cs(17,47): error CS1519: Invalid token ';' in a member declaration /Program.cs(18,1): error CS1022: Type or namespace definition, or end-of-file expected

However, there isn't a need to make a change to that as part of this PR.

jcouv · 2025-11-15T15:37:00Z

@CyrusNajmabadi Please consider trimming the commit message before merging. The multi-page OP description generated by Copilot doesn't seem to useful in the git history: 28b77b6

Initial plan

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Copilot AI assigned Copilot and CyrusNajmabadi Nov 3, 2025

Copilot started work on behalf of CyrusNajmabadi November 3, 2025 21:20 View session

Copilot AI and others added 3 commits November 3, 2025 21:47

Copilot AI changed the title ~~[WIP] Improve error recovery on missing type or identifier~~ Improve parser error recovery for property declarations with missing identifiers Nov 3, 2025

Copilot AI requested a review from CyrusNajmabadi November 3, 2025 22:01

Copilot finished work on behalf of CyrusNajmabadi November 3, 2025 22:01

CyrusNajmabadi added 5 commits November 3, 2025 14:57

Refine

648c539

Merge branch 'copilot/improve-error-recovery' of https://github.com/d…

35a75ad

…otnet/roslyn into copilot/improve-error-recovery

Update test

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Refine

4eb8881

Docs

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CyrusNajmabadi reviewed Nov 4, 2025

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src/Compilers/CSharp/Test/Syntax/Parsing/MemberDeclarationParsingTests.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of CyrusNajmabadi November 4, 2025 00:41 View session

Copilot AI requested a review from CyrusNajmabadi November 4, 2025 00:47

Copilot finished work on behalf of CyrusNajmabadi November 4, 2025 00:47

Restore

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CyrusNajmabadi reviewed Nov 4, 2025

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CyrusNajmabadi marked this pull request as ready for review November 4, 2025 20:09

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src/Compilers/CSharp/Portable/Parser/LanguageParser.cs Outdated Show resolved Hide resolved

CyrusNajmabadi and others added 2 commits November 4, 2025 18:05

Update src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

3c8097c

Co-authored-by: Rikki Gibson <rigibson@microsoft.com>

Merge remote-tracking branch 'upstream/main' into copilot/improve-err…

9d5f926

…or-recovery

CyrusNajmabadi requested a review from RikkiGibson November 6, 2025 19:52

jjonescz approved these changes Nov 10, 2025

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CyrusNajmabadi and others added 7 commits November 10, 2025 12:04

Update src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

f5d45ed

Co-authored-by: Jan Jones <janjones@microsoft.com>

Merge remote-tracking branch 'upstream/main' into copilot/improve-err…

2917a88

…or-recovery

newlines

c87eb1d

Switch to lowercase check

1c09847

remove comments

351fbc4

remove asserts

8631206

Simplify check

5b4996f

jjonescz approved these changes Nov 10, 2025

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RikkiGibson reviewed Nov 12, 2025

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RikkiGibson approved these changes Nov 12, 2025

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CyrusNajmabadi merged commit 28b77b6 into main Nov 12, 2025
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dotnet-policy-service bot added this to the Next milestone Nov 12, 2025

CyrusNajmabadi deleted the copilot/improve-error-recovery branch November 12, 2025 06:53

dotnet-bot mentioned this pull request Nov 14, 2025

[Automated] PRs inserted in VS build main-11213.22 #81230

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dotnet-maestro bot mentioned this pull request Dec 18, 2025

[main] Source code updates from dotnet/roslyn dotnet/dotnet#3957

Merged

davidwengier modified the milestones: Next, 18.3 Jan 6, 2026

		@@ -160,22 +160,22 @@ class Symbol

		void M(object o, bool b0, bool b1)

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Summary

Plan:

Technical Implementation:

Validation:

Remaining Work:

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CyrusNajmabadi commented Nov 11, 2025

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Copilot AI commented Nov 3, 2025 •

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