Turn off implicit clang modules while importing CU dependencies. #8752
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augusto2112
approved these changes
May 15, 2024
ModuleFileSharedCore::getTransitiveLoadingBehavior() has a best-effort mode that is enabled when debugger support is turned on that will try to import implementation-only imports of Swift modules, but won't treat import failures as errors. When explicit modules are on, this has the unwanted side-effect of potentially triggering an implicit Clang module build if one of the internal dependencies of a library was not used to build the target. To avoid these costly and potentially dangerous imports we turn off implicit modules while importing the CU imports only. If a user manually evaluates an expression that contains an import statement that can still trigger an implict import. Implicit imports can be dangerous if an implicit module depends on a module that also exists as an explicit input: In this case, a subsequent explicit import of said dependency will error because Clang now knows about two versions of the same module. rdar://127455779
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ModuleFileSharedCore::getTransitiveLoadingBehavior() has a best-effort mode that is enabled when debugger support is turned on that will try to import implementation-only imports of Swift modules, but won't treat import failures as errors. When explicit modules are on, this has the unwanted side-effect of potentially triggering an implicit Clang module build if one of the internal dependencies of a library was not used to build the target. To avoid these costly and potentially dangerous imports we turn off implicit modules while importing the CU imports only. If a user manually evaluates an expression that contains an import statement that can still trigger an implict import. Implicit imports can be dangerous if an implicit module depends on a module that also exists as an explicit input: In this case, a subsequent explicit import of said dependency will error because Clang now knows about two versions of the same module.
rdar://127455779