Fix await keyword recognition in interpolated strings with parentheses #80763

Copilot · 2025-10-16T15:06:47Z

Summary

Fixed the parser to properly recognize the await keyword inside interpolated string expressions when the awaited expression is wrapped in parentheses. The fix involves:

Passing the IsInAsync context from the outer parser to the temp parser created for interpolation expressions
Creating a new AsyncContext struct that follows the same pattern as FieldKeywordContext to manage the async state

Files Changed

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs: Added AsyncContext struct
src/Compilers/CSharp/Portable/Parser/LanguageParser_InterpolatedString.cs: Updated to pass and use IsInAsync
src/Compilers/CSharp/Test/Syntax/Parsing/AsyncParsingTests.cs: Added two simplified tests using raw string literals

Fixes #39149

Original prompt

This section details on the original issue you should resolve

<issue_title>Why 'await' causing compiler error when that in an interpolated string?</issue_title>
<issue_description>The following code cannot be compiled:

        private static async Task Main()
        {
            // compiler error CS0103 : The name 'await' does not exist in the current context
            var z = $"{await (Task.FromResult(string.Empty))}";

            // allowed
            var a = await Task.FromResult(string.Empty);
            var b = await (Task.FromResult(string.Empty));
            var c = $"{await Task.FromResult(string.Empty)}";

            Console.ReadLine();
        }
```</issue_description>

<agent_instructions>Copilot, this is likely in: src\Compilers\CSharp\Portable\Parser\LanguageParser_InterpolatedString.cs

note how the appropriate information is passed along such that we can determine if we're a 'FieldKeywordContext' when parsing interpolation contents.  We likely need to pass along the same information to state if IsInAsync is true for the parser.

Tests for this can go in AsyncParsingTests</agent_instructions>

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

<comments>
<comment_new><author>@CyrusNajmabadi</author><body>
Sounds like a bug to me.  Likely a compiler issue where the lexer/parser get confused as to what's inside the interpolation.  </body></comment_new>
</comments>

Fixes #39149

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Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-10-16T15:32:27Z

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

            using var _ = new FieldKeywordContext(tempParser, isInFieldKeywordContext);
+            using var __ = new AsyncContext(tempParser, isInAsync);


@copilot rename these to _1 and _2 as that is the normal patten we use when having multiple unnamed temps.

Done in commit 8c24cdc - renamed to _1 and _2.

CyrusNajmabadi · 2025-10-16T15:32:36Z

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

+        public void AwaitInInterpolatedString_WithParentheses()
+        {
+            UsingTree(@"
+class C


@copilot please use a raw string literals for all the tests.

Done in commit 8c24cdc - using raw string literals with triple quotes.

CyrusNajmabadi · 2025-10-16T15:33:03Z

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

+        [Fact]
+        // Tests that await keyword is recognized in interpolated strings with parentheses


@copilot please remove superflous comment. And please add an appropriate [WorkItem("url")] attribute to al the tests.

Done in commit 8c24cdc - removed comments and added [WorkItem("https://github.com/dotnet/roslyn/issues/39149")].

CyrusNajmabadi · 2025-10-16T15:34:16Z

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

+{
+    async System.Threading.Tasks.Task M()
+    {
+        var z = $""{await (System.Threading.Tasks.Task.FromResult(string.Empty))}"";


@copilot please simplify the test as it is only testing syntax. First, you an use UsingStatement to just test the var v = $"..."; line. second, the code inside the interpolation can be simpler, without such a complex expression inside the parenthesized region. This applies to both tests.

Done in commit 8c24cdc - simplified to minimal async method with just the interpolated string statement. Used UsingTree with simplified expression await (M()) and await M() inside the interpolation.

- Rename _ and __ to _1 and _2 per naming convention - Use raw string literals for test code - Add WorkItem attributes with issue URL - Simplify tests to minimal async method with interpolated string Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-10-20T17:26:30Z

@dotnet/roslyn-compiler ptal.

CyrusNajmabadi · 2025-10-30T17:21:27Z

@dotnet/roslyn-compiler ptal.

CyrusNajmabadi · 2025-11-03T16:43:04Z

@jjonescz can you ptal?

CyrusNajmabadi · 2025-11-04T19:59:12Z

@RikkiGibson could you ptal?

RikkiGibson · 2025-11-04T20:40:37Z

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

            using var tempParser = new LanguageParser(tempLexer, oldTree: null, changes: null);
-            using var _ = new FieldKeywordContext(tempParser, isInFieldKeywordContext);
+            using var _1 = new FieldKeywordContext(tempParser, isInFieldKeywordContext);
+            using var _2 = new AsyncContext(tempParser, isInAsync);


It looks like this does address the current bug, but, I am wondering if a more "holistic" way of forwarding state from a parent to child parser instance is warranted here. Or, at least something which forces the developer to make an explicit decision on whether/how to forward the state here, when state fields used by the parser are added/changed.

It seems likely that any expression whose parsing depends on fields in SyntaxFactoryContext, may behave incorrectly inside interpolations, if it is not forwarded here.

RikkiGibson

LGTM, I think it will be good to follow up and fix parsing state handling for interpolations more categorically.

CyrusNajmabadi · 2025-11-05T01:06:06Z

LGTM, I think it will be good to follow up and fix parsing state handling for interpolations more categorically.

Agreed. Will try an immediate followup.

Initial plan

6c571ba

Copilot AI assigned Copilot and CyrusNajmabadi Oct 16, 2025

Copilot started work on behalf of CyrusNajmabadi October 16, 2025 15:07 View session

Copilot AI and others added 2 commits October 16, 2025 15:19

Fix await in interpolated strings with parentheses

7feb93d

Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Address code review: Remove placeholder WorkItem attributes

dc11d60

Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix compiler error for 'await' in interpolated string~~ Fix await keyword recognition in interpolated strings with parentheses Oct 16, 2025

Copilot AI requested a review from CyrusNajmabadi October 16, 2025 15:27

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CyrusNajmabadi merged commit b1964bb into main Nov 5, 2025
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[main] Source code updates from dotnet/roslyn dotnet/dotnet#3147

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[release/10.0.2xx] Source code updates from dotnet/roslyn dotnet/dotnet#3244

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[Automated] PRs inserted in VS build main-11206.22 #81091

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[Automated] PRs inserted in VS build feature.debugger.main-11206.224 #81096

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		using var _ = new FieldKeywordContext(tempParser, isInFieldKeywordContext);
		using var __ = new AsyncContext(tempParser, isInAsync);

		[Fact]
		// Tests that await keyword is recognized in interpolated strings with parentheses

Fix await keyword recognition in interpolated strings with parentheses #80763

Fix await keyword recognition in interpolated strings with parentheses #80763

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Copilot AI commented Oct 16, 2025 •

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