incremental-build

Build twice with binary logs using dotnet build /bl:first.binlog and /bl:second.binlog, then search the second log for "Building target completely" and "is newer than output" messages. These reveal which targets ran and which input file triggered the rebuild.

Add both Inputs and Outputs attributes to the target so MSBuild compares file timestamps and skips it when outputs are newer. Register generated files in the FileWrites item group and write outputs to $(IntermediateOutputPath) for clean support.

Visual Studio uses its own Fast Up-to-Date Check separate from MSBuild's Inputs/Outputs mechanism, which can be wrong for custom targets or non-standard item types. Set DisableFastUpToDateCheck to true or enable verbose up-to-date check logging to diagnose.

FileWrites tracks files generated during the build so dotnet clean can remove them. Files created by custom targets but not registered accumulate across builds and can confuse incremental up-to-date checks.

Use Returns when you only need to pass items to calling targets without affecting incremental build checks. Outputs serves double duty as both the incremental timestamp comparison and the return value, while Returns only affects the return value.