Missing compatibility for plugins that don't declare any outputs in swiftbuild

[cmcgee1024]

Is it reproducible with SwiftPM command-line tools: swift build, swift test, swift package etc?

• Confirmed reproduction steps with SwiftPM CLI. The description text must include reproduction steps with either of command-line SwiftPM commands, swift build, swift test, swift package etc.

Description

The native build system has a compatibility mode for when the swift tools is < 5.11 so that it emits a warning, and doesn't run the plugin, which matches the behaviour in older toolchains. With the swiftbuild build system, the plugin is always run in spite of the swift tools version, even if it has no outputs.

There is a test case PluginTests.testBuildToolWithoutOutputs that reproduces this scenario and can be used to test the correct behaviour.

Expected behavior

No response

Actual behavior

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Steps to reproduce

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Swift Package Manager version/commit hash

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Swift & OS version (output of swift --version ; uname -a)

No response