LoggerMessage source generator does not work with logger from primary constructor.

[stmimon]

Description

The source generator for LoggerMessage does not work if the logger is injected from the primary constructor.

Reproduction Steps

Create the project.

• dotnet new classlib
• dotnet add package Microsoft.Extensions.Logging --version 8.0.0-preview.7.23375.6

Add the following c# file to the project.

using Microsoft.Extensions.Logging;

namespace Test;

public partial class LoggerFromPrimaryConstructor(ILogger<LoggerFromPrimaryConstructor> logger)
{
    [LoggerMessage(Level = LogLevel.Debug, Message = "This is a test")]
    public partial void LogTest();
}

Expected behavior

The source generator emits code with similar behaviour as if I had written the following.

public partial class LogWithExplicitProperty
{
    private readonly ILogger<LoggerFromPrimaryConstructor> logger;

    public LogWithExplicitProperty(ILogger<LoggerFromPrimaryConstructor> logger)
    {
        this.logger = logger;
    }

    [LoggerMessage(Level = LogLevel.Debug, Message = "This is a test")]
    public partial void LogTest();
}

Actual behavior

Compilation fails with error SYSLIB1019: Couldn't find a field of type Microsoft.Extensions.Logging.ILogger in class LoggerFromPrimaryConstructor.

I also got error CS1525: Invalid expression term '<' in another project where the source generator did find the logger for some reason, but generated incorrect code that referenced the logger by the symbol <logger>P. I assume this is the generated field name? I could not reproduce it however.

Regression?

This is not a regression, as primary constructors are not GA.

Known Workarounds

Use a regular constructor instead of a primary constructor.

Configuration

I am using .NET 8 preview 7 on Windows 10 Enterprise 22H2 x64.

Other information

No response

[ghost]

Tagging subscribers to this area: @dotnet/area-extensions-logging
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

The source generator for LoggerMessage does not work if the logger is injected from the primary constructor.

Reproduction Steps

Create the project.

• dotnet new classlib
• dotnet add package Microsoft.Extensions.Logging --version 8.0.0-preview.7.23375.6

Add the following c# file to the project.

using Microsoft.Extensions.Logging;

namespace Test;

public partial class LoggerFromPrimaryConstructor(ILogger<LoggerFromPrimaryConstructor> logger)
{
    [LoggerMessage(Level = LogLevel.Debug, Message = "This is a test")]
    public partial void LogTest();
}

Expected behavior

The source generator emits code with similar behaviour as if I had written the following.

public partial class LogWithExplicitProperty
{
    private readonly ILogger<LoggerFromPrimaryConstructor> logger;

    public LogWithExplicitProperty(ILogger<LoggerFromPrimaryConstructor> logger)
    {
        this.logger = logger;
    }

    [LoggerMessage(Level = LogLevel.Debug, Message = "This is a test")]
    public partial void LogTest();
}

Actual behavior

Compilation fails with error SYSLIB1019: Couldn't find a field of type Microsoft.Extensions.Logging.ILogger in class LoggerFromPrimaryConstructor.

I also got error CS1525: Invalid expression term '<' in another project where the source generator did find the logger for some reason, but generated incorrect code that referenced the logger by the symbol <logger>P. I assume this is the generated field name? I could not reproduce it however.

Regression?

This is not a regression, as primary constructors are not GA.

Known Workarounds

Use a regular constructor instead of a primary constructor.

Configuration

I am using .NET 8 preview 7 on Windows 10 Enterprise 22H2 x64.

Other information

No response

Author:	stmimon
Assignees:	-
Labels:	area-Extensions-Logging
Milestone:	-

[tarekgh]

Yes, the primary constructors feature is a new compiler feature and is not supported yet with the logging source gen. This is something we can consider supporting in future releases. Thanks for your report.

CC @geeknoid

[sloncho]

@tarekgh 8.0 is now GA and long-term support. Fixing this for 9.0 will leave more than 2 years with unsupported code.

[tarekgh]

@sloncho we usually get issues after facts which we address it in the next releases. If we find demands on specific issue, we consider porting the fix back to the service release.

[stmimon]

@sloncho If you want to use a primary constructor, another workaround is to explicitly pass the logger instance to the logging methods.

[LoggerMessage(Level = LogLevel.Debug, Message = "This is a test")]
public partial void LogTest(ILogger logger);

[timia2109]

Or you could do something like this:

public partial class Foo(ILogger<Foo> logger) {
    private readonly ILogger _logger = logger;
}