Xcode build fails while editing sources

Number:rdar://FB7629752 Date Originated:Mar 17, 2020 at 5:42 PM
Status:Open Resolved:
Product:Xcode Product Version:Version 11.3.1 (11C504)
Classification: Reproducible:yes
Very simply Xcode build fails while editing Swift code sources. This issue has always existed for Swift in any version of Xcode that supported it as far as i know. 

> Please list the steps you took to reproduce the issue:
1. start compiling an above average sized project
2. edit any source file (during the compile sources phase, but i am not sure, the issue seems not fully deterministic, i'd say 80% of cases)

> What did you expect to happen?
3. the compiler successfully completes (utilizin an image of the edited file at the moment it was either began to be parsed or the compilation started)

> What actually happened?
3. the compilation fails with following error:

    <unknown>:0: error: input file 'xxx.swift' was modified during the build
    Command CompileSwiftSources failed with a nonzero exit code


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