[LSG] LoggerMessage - Add diagnostic - Can't have malformed format strings

[maryamariyan]

Refer to: #51064 (comment)

Proposal

The proposed diagnostic descriptor would be:

public static DiagnosticDescriptor MalformedFormatStrings { get; } = new DiagnosticDescriptor(
    id: "SYSLIB1022",
    title: new LocalizableResourceString(nameof(SR.MalformedFormatStringsTitle), SR.ResourceManager, typeof(FxResources.Microsoft.Extensions.Logging.Generators.SR)),
    messageFormat: new LocalizableResourceString(nameof(SR.MalformedFormatStringsMessage), SR.ResourceManager, typeof(FxResources.Microsoft.Extensions.Logging.Generators.SR)),
    category: "LoggingGenerator",
    DiagnosticSeverity.Error,
    isEnabledByDefault: true);

With the following title:

Logging method contains malformed format strings

And the following message format:

Logging method '{0}' contains malformed format strings

Note: SYSLIB1022 diagnostic is already merged on main, but it is not being triggered.

Code Sample

The diagnostic would be triggered for case such as the following ones:

IReadOnlyList<Diagnostic> diagnostics = await RunGenerator(@"
    partial class C
    {
        [LoggerMessage(EventId = 1, Level = LogLevel.Debug, Message = ""M1 {A} M1 { M3"")]
        static partial void M1(ILogger logger);

        [LoggerMessage(EventId = 2, Level = LogLevel.Debug, Message = ""M2 {A} M2 } M2"")]
        static partial void M2(ILogger logger);

        [LoggerMessage(EventId = 3, Level = LogLevel.Debug, Message = ""M3 {arg1"")]
        static partial void M3(ILogger logger);

        [LoggerMessage(EventId = 4, Level = LogLevel.Debug, Message = ""M4 arg1}"")]
        static partial void M4(ILogger logger);

        [LoggerMessage(EventId = 5, Level = LogLevel.Debug, Message = ""M5 {"")]
        static partial void M5(ILogger logger);

        [LoggerMessage(EventId = 6, Level = LogLevel.Debug, Message = ""}M6 "")]
        static partial void M6(ILogger logger);

        [LoggerMessage(EventId = 7, Level = LogLevel.Debug, Message = ""M7 {{arg1}}"")]
        static partial void M7(ILogger logger);

        [LoggerMessage(EventId = 8, Level = LogLevel.Debug, Message = ""}M8{arg1}{arg2}"")]
        static partial void M8(ILogger logger);
    }
");

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Issue Details

---

Cases for which this diagnostic would be helpful:

[LoggerMessage(EventId = 3, Level = LogLevel.Debug, Message = ""M3 {arg1"")]
static partial void M3(ILogger logger);

[LoggerMessage(EventId = 4, Level = LogLevel.Debug, Message = ""M4 arg1}"")]
static partial void M4(ILogger logger);

[LoggerMessage(EventId = 5, Level = LogLevel.Debug, Message = ""M5 {"")]
static partial void M5(ILogger logger);

[LoggerMessage(EventId = 6, Level = LogLevel.Debug, Message = ""}M6 "")]
static partial void M6(ILogger logger);

Author:	maryamariyan
Assignees:	-
Labels:	area-Extensions-Logging, untriaged
Milestone:	-