Xcode does not pass all -fmodule-map-file flags to SourceKit

Number:rdar://36107040 Date Originated:Dec 18 2017
Status:Closed Resolved:July 5 2018
Product:Developer Tools Product Version:9.1
Classification:Bug Reproducible:Always
Summary: When Xcode makes a 'source.request.editor.open.interface' request to SourceKit, Xcode will only include the last -fmodule-map-file argument even if the file's build settings has multiple -fmodule-map-file present. Note that Xcode does pass all -fmodule-map-files when making a 'source.request.cursorinfo' request to SourceKit.

This is reproducible even with Swift Package Manager, which seems to use a workaround for this apparent issue: https://github.com/apple/swift-package-manager/blob/6bac701d2b730434681205273897be91cbd67212/Sources/Xcodeproj/pbxproj().swift#L595 (this bug report is a possible duplicate of radar/30071677). Their workaround is hacky (has side effects if other things are included in the directory containing the module map) and may also lead into https://llvm.org/bugs/show_bug.cgi?id=19501. When not using this workaround, one is not able to view any of the modules included via -fmodule-map-file besides the one for the last -fmodule-map-file argument given. 

Expected Results:
Xcode passes all -fmodule-map-file arguments to SourceKit

Actual Results:
Xcode passes only the last -fmodule-map-file argument to SourceKit

Xcode 9.1, but also reproduced on Xcode 9.2, Xcode 9.1, and Xcode 8.3.3 (didn't try reproducing further back)


Fixed in Xcode 10 beta 3.

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