incremental-build

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Guide for optimizing MSBuild incremental builds. Only activate in MSBuild/.NET build context. USE FOR: builds slower than expected on subsequent runs, 'nothing changed but it rebuilds anyway', diagnosing why targets re-execute unnecessarily, fixing broken no-op builds. Covers 8 common causes: missing Inputs/Outputs on custom targets, volatile properties in output paths (timestamps/GUIDs), file writes outside tracked Outputs, missing FileWrites registration, glob changes, Visual Studio Fast Up-to-Date Check (FUTDC) issues. Key diagnostic: look for 'Building target completely' vs 'Skipping target' in binlog. DO NOT USE FOR: first-time build slowness (use build-perf-baseline), parallelism issues (use build-parallelism), evaluation-phase slowness (use eval-performance), non-MSBuild build systems. INVOKES: dotnet build /bl, binlog replay with diagnostic verbosity.

Web & Frontend 3,219 stars 238 forks Updated today MIT

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Skill Content

## How MSBuild Incremental Build Works MSBuild's incremental build mechanism allows targets to be skipped when their outputs are already up to date, dramatically reducing build times on subsequent runs. - **Targets with `Inputs` and `Outputs` attributes**: MSBuild compares the timestamps of all files listed in `Inputs` against all files listed in `Outputs`. If every output file is newer than every input file, the target is skipped entirely. - **Without `Inputs`/`Outputs`**: The target runs every time the build is invoked. This is the default behavior and the most common cause of slow incremental builds. - **`Incremental` attribute on targets**: Targets can explicitly opt in or out of incremental behavior. Setting `Incremental="false"` forces the target to always run, even if `Inputs` and `Outputs` are specified. - **Timestamp-based comparison**: MSBuild uses file system timestamps (last write time) to determine staleness. It does not use content hashes. This means touching a file (updating its timestamp without changing content) will trigger a rebuild. ```xml <!-- This target is incremental: skipped if Output is newer than all Inputs --> <Target Name="Transform" Inputs="@(TransformFiles)" Outputs="@(TransformFiles->'$(OutputPath)%(Filename).out')"> <!-- work here --> </Target> <!-- This target always runs because it has no Inputs/Outputs --> <Target Name="PrintMessage"> <Message Text="This runs every build" /> </Target> ``` ## Why Incremental Builds B...

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Author
dotnet
Repository
dotnet/skills
Created
3 months ago
Last Updated
today
Language
C#
License
MIT

Similar Skills

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Web & Frontend Solid

build-perf-baseline

Establish build performance baselines and apply systematic optimization techniques. Only activate in MSBuild/.NET build context. USE FOR: diagnosing slow builds, establishing before/after measurements (cold, warm, no-op scenarios), applying optimization strategies like MSBuild Server, static graph builds, artifacts output, and dependency graph trimming. Start here before diving into build-perf-diagnostics, incremental-build, or build-parallelism. DO NOT USE FOR: non-MSBuild build systems, detailed bottleneck analysis (use build-perf-diagnostics after baselining).

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build-perf-diagnostics

Diagnose MSBuild build performance bottlenecks using binary log analysis. Only activate in MSBuild/.NET build context. USE FOR: identifying why builds are slow by analyzing binlog performance summaries, detecting ResolveAssemblyReference (RAR) taking >5s, Roslyn analyzers consuming >30% of Csc time, single targets dominating >50% of build time, node utilization below 80%, excessive Copy tasks, NuGet restore running every build. Covers timeline analysis, Target/Task Performance Summary interpretation, and 7 common bottleneck categories. Use after build-perf-baseline has established measurements. DO NOT USE FOR: establishing initial baselines (use build-perf-baseline first), fixing incremental build issues (use incremental-build), parallelism tuning (use build-parallelism), non-MSBuild build systems. INVOKES: dotnet msbuild binlog replay with performancesummary, grep for analysis.

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Data & Documents Solid

including-generated-files

Fix MSBuild targets that generate files during the build but those files are missing from compilation or output. Only activate in MSBuild/.NET build context. USE FOR: generated source files not compiling (CS0246 for a type that should exist), custom build tasks that create files but they are invisible to subsequent targets, globs not capturing build-generated files because they expand at evaluation time before execution creates them, ensuring generated files are cleaned by the Clean target. Covers correct BeforeTargets timing (CoreCompile, BeforeBuild, AssignTargetPaths), adding to Compile/FileWrites item groups, using $(IntermediateOutputPath) instead of hardcoded obj/ paths. DO NOT USE FOR: C# source generators that already work via the Roslyn pipeline, T4 design-time generation that runs in Visual Studio, non-MSBuild build systems. INVOKES: no tools — pure knowledge skill.

3,219 Updated today
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Data & Documents Solid

eval-performance

Guide for diagnosing and improving MSBuild project evaluation performance. Only activate in MSBuild/.NET build context. USE FOR: builds slow before any compilation starts, high evaluation time in binlog analysis, expensive glob patterns walking large directories (node_modules, .git, bin/obj), deep import chains (>20 levels), preprocessed output >10K lines indicating heavy evaluation, property functions with file I/O ($([System.IO.File]::ReadAllText(...))), multiple evaluations per project. Covers the 5 MSBuild evaluation phases, glob optimization via DefaultItemExcludes, import chain analysis with /pp preprocessing. DO NOT USE FOR: compilation-time slowness (use build-perf-diagnostics), incremental build issues (use incremental-build), non-MSBuild build systems. INVOKES: dotnet msbuild -pp:full.xml for preprocessing, /clp:PerformanceSummary.

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Web & Frontend Solid

build-parallelism

Guide for optimizing MSBuild build parallelism and multi-project scheduling. Only activate in MSBuild/.NET build context. USE FOR: builds not utilizing all CPU cores, speeding up multi-project solutions, evaluating graph build mode (/graph), build time not improving with -m flag, understanding project dependency topology. Note: /maxcpucount default is 1 (sequential) — always use -m for parallel builds. Covers /maxcpucount, graph build for better scheduling and isolation, BuildInParallel on MSBuild task, reducing unnecessary ProjectReferences, solution filters (.slnf) for building subsets. DO NOT USE FOR: single-project builds, incremental build issues (use incremental-build), compilation slowness within a project (use build-perf-diagnostics), non-MSBuild build systems. INVOKES: dotnet build -m, dotnet build /graph, binlog analysis.

3,219 Updated today
dotnet