[Build] Skip XamlC when no XAML files need XamlC processing#34972
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davidnguyen-tech wants to merge 5 commits intodotnet:net11.0from
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[Build] Skip XamlC when no XAML files need XamlC processing#34972davidnguyen-tech wants to merge 5 commits intodotnet:net11.0from
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🚀 Dogfood this PR with:
curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34972Or
iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34972" |
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XamlC's validate-only pass (Debug default) is the only build-time XAML validation for files using the Runtime or XamlC inflators. SourceGen-only files are validated by XSG itself, so XamlC is redundant for them. Gate the XamlC target on '@(_MauiXaml_XC)' != '' OR '@(_MauiXaml_RT)' != '' (equivalent to '@(_MauiXaml_AsEmbeddedResource)' != ''). Projects using SourceGen exclusively — the default in net11.0 — now skip XamlC entirely. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Tests that don't care about XamlC now lock in the SourceGen default: they assert the build still succeeds and XamlC.stamp is absent. Tests whose subject is the XamlC target itself (incrementality, Clean, DesignTimeBuild contrast, AddNewFile) opt in via -p:MauiXamlInflator=XamlC -p:NoWarn=MAUI1001 so the existing contract is verifiable. Plan originally called for the SourceGen,XamlC combo, but for these synthesised projects the source generator emits a duplicate InitializeComponent (CS0111) when both inflators are active, so the bare XamlC form with NoWarn=MAUI1001 is used instead to silence the deprecation warning under the repo-wide TreatWarningsAsErrors setting. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Extract XamlC opt-in args + rationale to a single const so the 'why bare XamlC, not SourceGen,XamlC' explanation lives in one place. Apply the same opt-in to TouchXamlFile's body for future-proofing. Reword the misleading inline comment on the DesignTimeBuild precondition. Note: the prior commit message's TreatWarningsAsErrors rationale for NoWarn=MAUI1001 is slightly inaccurate — the synthesized projects under tempDirectory write a fresh Directory.Build.props that does not chain in the repo-root TWAE setting. NoWarn is kept anyway for noise reduction and to be robust if the chain ever changes. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
The XamlC target is gated to SourceGen-default-empty projects in this PR's targets change. Tests that simulated XamlC running on the synthesised single-project scaffold (TargetsShouldSkip, Clean, DesignTimeBuild, AddNewFile, TouchXamlFile) were exercising a code path that no longer executes by default. Delete them along with the XamlCOptIn constant. The contract that XamlC does not run by default is already locked in by BuildAProject, LinkedFile, RandomXml, RandomEmbeddedResource (AssertDoesNotExist on XamlC.stamp), and by NoXamlFiles (log-scrape that the target isn't scheduled). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Replace the single-line header comment with a block that makes explicit the contract the surviving tests protect: SourceGen is the net11.0 default and the XamlC target must not run on default builds. Addresses reviewer feedback on dotnet#34972 that future contributors had no in-file guidance that these are negative tests. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Skip the XamlC MSBuild target when both
_MauiXaml_SGand_MauiXaml_XCitem groups are empty — meaning no XAML files use the SourceGen or XamlC inflator.Motivation
In Debug builds, XamlC runs in
ValidateOnly=Truemode, loading the compiled assembly via Cecil, parsing all XAML, validating it, then discarding the result. When all XAML files use the SourceGen inflator (the default), this validation is redundant because the Source Generator already validates XAML at compile time.Changes
Microsoft.Maui.Controls.targets: AddedAND ('@(_MauiXaml_SG)' != '' OR '@(_MauiXaml_XC)' != '')to the XamlC target conditionMSBuildTests.cs: Added two tests:XamlCSkippedWhenRuntimeInflatorOnly— verifies XamlC is skipped when all XAML uses Runtime inflatorXamlCRunsWhenXamlCInflatorUsed— verifies XamlC still runs when XamlC inflator is usedTarget Ordering
_MauiXamlComputeInflator(which populates_MauiXaml_SG/_MauiXaml_XC) runs before Compile viaPrepareResourcesDependsOn. XamlC runsAfterTargets="AfterCompile", so MSBuild evaluates XamlC's condition after the item groups are fully populated.Impact
This primarily benefits builds where all XAML uses the Runtime inflator (deprecated path). The default SourceGen path still runs XamlC for validation. A follow-up optimization could skip XamlC's validate-only pass for SourceGen files, since SourceGen already self-validates.