binlog-failure-analysis

# Analyzing MSBuild Failures with Binary Logs This skill diagnoses MSBuild build failures from a `.binlog` file. The preferred path uses the **binlog MCP server** (`Microsoft.AITools.BinlogMcp`, exposed under the `binlog` MCP namespace) which is bundled with this plugin. If the MCP server is not available, fall back to the **binlog replay** workflow at the bottom. ## Primary workflow — binlog MCP The MCP server exposes structured tools for inspecting a `.binlog` without parsing text logs. Call them directly instead of replaying the binlog to a text file. Call `tools/list` for the MCP first if you are unsure which tools are available. **Important constraints:** - The `.binlog` file is a **binary format** — do NOT try to `cat`, `head`, `strings`, or read it directly. Use only the MCP tools to query it. - The **original source/project files might or might NOT be available on disk**. Project files (.csproj, .props, .targets, App.config, etc.) - if you cannot locate them on disk, they can only be read from within the binlog via MCP tools (e.g., embedded/source file retrieval). - **Synthesize findings as you go.** Do not spend all available time investigating — once you have enough evidence, present your conclusions. A partial answer with clear reasoning is better than timing out mid-investigation. Use the available MCP server tools to query the binary log for: - Build errors and warnings - MSBuild properties and their values - MSBuild items (PackageReference, ProjectReference, etc.) - Project evaluation data - Target execution details - File contents embedded in the binlog ## Fallback workflow — text-log replay (when MCP is unavailable) Use this only when the MCP server cannot be started (for example, on an older SDK or in an offline environment). ### Replay the binlog to text logs ```bash dotnet msbuild build.binlog -noconlog \ -fl "-flp:v=diag;logfile=full.log;performancesummary" \ -fl1 "-flp1:errorsonly;logfile=errors.log" \ -fl2 "-flp2:warningsonly;logfile=warnings.log" ``` > **PowerShell note:** Use `-flp:"v=diag;logfile=full.log;performancesummary"` > (quoted semicolons). ### Search the text logs ```bash cat errors.log grep -n -B2 -A2 "CS0246" full.log grep -i "CoreCompile.*FAILED\|Build FAILED\|error MSB" full.log grep 'Target "CoreCompile"' full.log | grep -oP 'project "[^"]*"' ``` ## Generating a binlog (only if none exists) ```bash dotnet build /bl:build.binlog ```