Add support for MSBUILD_LOGGING_ARGS #12993
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Document the process for enabling binary logging in CI/CD pipelines using environment variables, including supported arguments, argument processing order, and implementation flow. Fixes #12804
### Context Today it's possible to provide the `-bl` flag multiple times, but the behavior of the engine is that the last-provided flag wins. This is confusing, and in extreme cases can mean that tools that need binlogs and provide them via things like response files can be overridden by a user's invocation. Tools like CodeQL have a harder time adopting binlog usage for C# code analysis because they can't control where the binlog is generated. ### Changes Made Implemented support for writing multiple binlogs when supplied via command line arguments. The implementation intelligently handles two scenarios: 1. **Same Configuration (Optimized)**: When all `-bl` flags have the same configuration (only file paths differ), a single BinaryLogger writes to one location and copies to additional destinations at build completion for consistency and performance. 2. **Different Configurations**: When `-bl` flags have different configurations (e.g., `ProjectImports=None` vs `ProjectImports=Embed`), separate BinaryLogger instances are created to respect each configuration. **Key changes:** - Added `AdditionalFilePaths` property to BinaryLogger with `init` accessor (documented as internal-use only) - Added `BinaryLogger.ProcessParameters()` static method to process multiple parameter sets and return distinct paths with configuration info - Added `ProcessedBinaryLoggerParameters` readonly struct to encapsulate the processing results - Updated `Shutdown()` method to copy binlog to additional paths after stream close - Uses `LogMessage` to log copy destinations before stream close - Uses `Console.Error` to log copy errors (won't fail build on copy failures) - Updated `XMake.ProcessBinaryLogger()` to use the new BinaryLogger.ProcessParameters() method with object initializer syntax for `init` properties - Added error message resource for copy failures - Replaced hardcoded string literals with constants (BinlogFileExtension, LogFileParameterPrefix) - All new methods have XML documentation - Added `DuplicateFilePaths` property to track and report duplicate paths - Added message to inform users when duplicate binary log paths are filtered out - Refactored `TryInterpretPathParameter` methods to eliminate code duplication via shared core method - Optimized `ProcessParameters` to avoid redundant path extraction calls ### Testing - Added unit tests for multiple binlog files with same configuration - Added unit tests for multiple binlog files with different configurations - Added unit test for duplicate path deduplication - Added dedicated unit tests for `ExtractFilePathFromParameters`, `ExtractNonPathParameters`, and `ProcessParameters` - Manual verification confirms all specified binlog files are created with identical content - All tests passing with `init` accessor implementation ### Notes - The `AdditionalFilePaths` property uses `init` accessor to enforce immutability after object initialization, signaling it should only be set during construction - External code should create multiple logger instances instead of using AdditionalFilePaths - When MSBUILDDEBUGENGINE is set, the engine creates a separate BinaryLogger instance which operates independently (functionally correct behavior) - Duplicate paths specified via multiple `-bl` flags are automatically deduplicated - only the first occurrence is kept - Users are now informed when duplicate paths are detected and filtered out - Copy errors are logged to stderr but don't fail the build, ensuring builds succeed even if binlog copies fail <!-- START COPILOT CODING AGENT SUFFIX --> <details> <summary>Original prompt</summary> > > ---- > > *This section details on the original issue you should resolve* > > <issue_title>MSBuild.exe should support writing multiple binlogs if supplied as part of command line arguments</issue_title> > <issue_description>### Summary > > Today it's possible to provide the `-bl` flag multiple times, but the behavior of the engine is that the last-provided flag wins: > > ``` > > dotnet build -bl:1.binlog -bl:2.binlog > Restore complete (0.1s) > info NETSDK1057: You are using a preview version of .NET. See: https://aka.ms/dotnet-support-policy > lib2 net10.0 succeeded (0.1s) → D:\Code\scratch\bleh\lib2\bin\Debug\net10.0\lib2.dll > bleh net10.0 succeeded (0.1s) → bin\Debug\net10.0\bleh.dll > > Build succeeded in 0.5s > > ls *.binlog > > Directory: D:\Code\scratch\bleh\lib > > Mode LastWriteTime Length Name > ---- ------------- ------ ---- > -a--- 10/29/2025 11:14 AM 454756 2.binlog > ``` > This is confusing, and in extreme cases can mean that tools that need binlogs and provide them via things like response files can be overridden by a users invocation. > > ### Background and Motivation > > The inability to write more than one binlog file means that tools like codeql have a harder time adopting binlog usage for C# code analysis, because they can't control where the binlog is generated. > > ### Proposed Feature > > The command-line handling should accept _multiple_ bl flags, resolve them into their distinct binlog filenames, ensure that set is distinct, and then the binary logger should be able to write binary logs to all of those specified files. > > This file writing could be done in two ways (at least) > * multiple independent writers, each writing to a separate file > * one writer, writing the binlog file to a temp location and then atomically copying that file to the various destinations at build-finish > > We should use the second option for consistency. > > > ### Alternative Designs > > _No response_</issue_description> > > ## Comments on the Issue (you are @copilot in this section) > > <comments> > </comments> > </details> - Fixes #12705 <!-- START COPILOT CODING AGENT TIPS --> --- 💡 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](https://gh.io/copilot-coding-agent-tips) in the docs. --------- Co-authored-by: copilot-swe-agent[bot] <[email protected]> Co-authored-by: baronfel <[email protected]> Co-authored-by: YuliiaKovalova <[email protected]> Co-authored-by: YuliiaKovalova <[email protected]>
Document the process for enabling binary logging in CI/CD pipelines using environment variables, including supported arguments, argument processing order, and implementation flow. Fixes #12804
baronfel
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Jan 9, 2026
baronfel
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Jan 9, 2026
baronfel
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Jan 9, 2026
baronfel
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Jan 9, 2026
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Worth noting that the branch protections preventing merge aren't active on this branch due to the naming - if we're going to use the |
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it's a temp measure , we haven't agreed on this approach yet with @rainersigwald |
baronfel
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Jan 12, 2026
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Pull request overview
This PR implements support for the MSBUILD_LOGGING_ARGS environment variable, allowing CI/CD pipelines to enable diagnostic logging (binary logs) without modifying project files or build scripts. Only -bl and -check arguments are supported through this environment variable.
Changes:
- Added environment variable processing for
MSBUILD_LOGGING_ARGSinCommandLineParser.GatherLoggingArgsEnvironmentVariableSwitches - Extended
DeferredBuildMessagestruct to support warning messages with error codes - Updated localization resource files with new error messages for the feature
- Added comprehensive unit tests for the new functionality
Reviewed changes
Copilot reviewed 32 out of 32 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
| src/MSBuild/XMake.cs | Updated GatherAllSwitches calls to pass deferred build messages; changed s_globalMessagesToLogInBuildLoggers from readonly to mutable |
| src/MSBuild/CommandLine/CommandLineParser.cs | Added GatherLoggingArgsEnvironmentVariableSwitches method to parse and validate logging args from environment variable |
| src/Framework/Traits.cs | Added constants and properties for MSBUILD_LOGGING_ARGS environment variables |
| src/Build/BackEnd/BuildManager/BuildManager.cs | Extended DeferredBuildMessage with severity enum and new constructor; updated LogDeferredMessages to handle warnings |
| src/MSBuild/Resources/Strings.resx | Added three new localized strings for logging args diagnostics |
| src/MSBuild/Resources/xlf/*.xlf | Updated all localization files with new strings marked as "new" state |
| src/Build/Resources/xlf/*.xlf | Reset existing translation strings to "new" state for re-translation |
| src/MSBuild.UnitTests/XMake_BinlogSwitch_Tests.cs | Added comprehensive test coverage for the new feature |
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Fixes #12804
Summary
This PR implements the MSBUILD_LOGGING_ARGS environment variable feature as described in the design spec (#12805). This allows enabling binary logging collection in CI/CD pipelines without modifying project files or build scripts.
Motivation
In CI/CD environments, it's often desirable to enable diagnostic logging (binary logs) for all builds without:
Modifying project files or .rsp files on disk
Changing build scripts
Affecting local developer builds
This feature enables centralized build diagnostics configuration through environment variables.
Testing
Add comprehensive UT coverage .
connected to #12706