S4TF Optional CHECK-AST Error

s4tf_check_ast

SWIFT_VERSION=4, asan_runtime, asserts, autolink-extract, crash-recovery, executable_test, fuzzer_runtime, no_asan, no_lto, nonexecutable_test, optimized_stdlib, optimized_stdlib_x86_64, shell, sourcekit, swift-remoteast-test, swift_interpreter, swift_stdlib_no_asserts,
swift_test_mode_optimize_none, swift_test_mode_optimize_none_x86_64, tools-release, ubsan_runtime                    
FAIL: Swift(linux-x86_64) :: AutoDiff/autodiff_function_silgen.swift (31 of 12142)
******************** TEST 'Swift(linux-x86_64) :: AutoDiff/autodiff_function_silgen.swift' FAILED ********************
Script:                            
--                                            
: 'RUN: at line 1';   /home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/bin/swift -frontend -target x86_64-unknown-linux-gnu  -module-cache-path '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/swift-t
est-results/x86_64-unknown-linux-gnu/clang-module-cache' -swift-version 4   -dump-ast /home/sftf/swift-source/swift/test/AutoDiff/autodiff_function_silgen.swift 2>&1 | '/usr/bin/python' '/home/sftf/swift-source/swift/utils/PathSanitizingFileCheck' --sanitize BUILD_DIR='/
home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64' --sanitize SOURCE_DIR='/home/sftf/swift-source/swift' --use-filecheck '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/llvm-linux-x86_64/bin/FileCheck'  /home/sftf/swift-
source/swift/test/AutoDiff/autodiff_function_silgen.swift -check-prefix=CHECK-AST
: 'RUN: at line 2';   /home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/bin/swift -frontend -target x86_64-unknown-linux-gnu  -module-cache-path '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/swift-t
est-results/x86_64-unknown-linux-gnu/clang-module-cache' -swift-version 4   -emit-silgen /home/sftf/swift-source/swift/test/AutoDiff/autodiff_function_silgen.swift | '/usr/bin/python' '/home/sftf/swift-source/swift/utils/PathSanitizingFileCheck' --sanitize BUILD_DIR='/ho
me/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64' --sanitize SOURCE_DIR='/home/sftf/swift-source/swift' --use-filecheck '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/llvm-linux-x86_64/bin/FileCheck'  /home/sftf/swift-so
urce/swift/test/AutoDiff/autodiff_function_silgen.swift -check-prefix=CHECK-SILGEN
: 'RUN: at line 3';   /home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/bin/swift -frontend -target x86_64-unknown-linux-gnu  -module-cache-path '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64/swift-t
est-results/x86_64-unknown-linux-gnu/clang-module-cache' -swift-version 4   -emit-sil /home/sftf/swift-source/swift/test/AutoDiff/autodiff_function_silgen.swift | '/usr/bin/python' '/home/sftf/swift-source/swift/utils/PathSanitizingFileCheck' --sanitize BUILD_DIR='/home/
sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/swift-linux-x86_64' --sanitize SOURCE_DIR='/home/sftf/swift-source/swift' --use-filecheck '/home/sftf/swift-source/build/Ninja-ReleaseAssert+stdlib-Release/llvm-linux-x86_64/bin/FileCheck'  /home/sftf/swift-sourc
e/swift/test/AutoDiff/autodiff_function_silgen.swift -check-prefix=CHECK-SIL
--                   
Exit Code: 1    
                                                 
Command Output (stderr):
--                           
/home/sftf/swift-source/swift/test/AutoDiff/autodiff_function_silgen.swift:21:15: error: CHECK-AST: expected string not found in input
// CHECK-AST: (function_conversion_expr implicit type='(Float) -> Float'  
              ^
<stdin>:29:15: note: scanning from here             
 (return_stmt range=[SOURCE_DIR/test/AutoDiff/autodiff_function_silgen.swift:10:3 - line:10:10]
              ^
<stdin>:30:2: note: possible intended match here
 (function_conversion_expr implicit type='(Float) -            
 ^
                      
--