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This allows developers to control whether these diagnostics are considered errors when `-warnings-as-errors` is specified. Resolves rdar://157694667.
27 lines
1.1 KiB
Markdown
27 lines
1.1 KiB
Markdown
# Missing module version (ModuleVersionMissing)
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Warnings that indicate the compiler cannot resolve an `#if canImport(<ModuleName>, _version: <version>)` directive because the module found was not built with a `-user-module-version` flag.
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## Overview
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Developers may conditionalize which code is active in a source file based on the module version number of an imported dependency module, like this:
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```swift
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import Dependency
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#if canImport(Dependency, _version: 1.2)
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// Use declarations introduced in version 1.2 of Dependency
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#else
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// ...
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#endif
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```
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A dependency's module version must be established by passing the `-user-module-version` flag when compiling the sources of the dependency the module. If no `-user-module-version` flag was specified when the dependency module was built, then the compiler will warn that it cannot resolve the `#if canImport` directive:
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```
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warning: cannot find user version number for module 'Dependency'; version number ignored [#ModuleVersionMissing]
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```
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If this diagnostic is emitted, then the `#if canImport` directive implicitly evaluates true.
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