Fixed stack overflow during execution of MacroEvaluationProgram #997
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asevko
requested review from
aciidgh,
jakepetroules,
mhrawdon,
neonichu and
owenv
as code owners
Author
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@jakepetroules can you please run CI tests? I don't have permission for that. Thanks in advance! |
Member
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@swift-ci please test |
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@swift-ci test |
owenv
reviewed
Jan 5, 2026
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owenv
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one small comment, otherwise this change lgtm
Author
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@owenv Thanks for review! I've fixed your comment |
owenv
approved these changes
Jan 5, 2026
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@swift-ci test |
Author
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@owenv the Swift Test macOS Platform (Swift main) failed with following assertation: It doesn't seem, that it's connected with that PR |
Collaborator
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@swift-ci test macOS |
Author
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Pull request / Test / Swift SDK for Android Build (nightly-main - noble - NDK r27d) (pull_request) failed with |
Collaborator
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that's a known issue in the android job, we can merge this |
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During the migration of a large project (~1800 targets) to a new version of Xcode, we faced constant build system crashes.
The first crash occurred during recursive
lookupMacroDeclarationandlookupConditionParameterevaluation, which is being fixed in #992.A second crash appeared in multiple places but always reduced to
MacroEvaluationProgram.executeInContext. Evaluating the instructionevalNamedMacroand then callingvalue.expression.evaluate(context:resultBuilder:alwaysEvalAsString)blew the call stack.This PR converts that recursive evaluation of the value expression to a stack-based approach that can handle any depth.
Each frame on the stack represents an in-progress evaluation of a macro expression. When we need to evaluate a nested macro, instead of making a recursive call, we push the current state onto the stack and start evaluating the nested expression. When we complete an expression evaluation, we pop the stack and continue.
This fix, combined with the one in #992, resolves the issue described in https://forums.swift.org/t/xcode-15-3-xcbuildservice-crash-infinite-loop-when-building-ios-project/70643/7.