Running jextract with any header with function declaration with more verbose output than FINE will cause UnsupportedOperationException be thrown for each function declaration.

Example,

Process tree junk3
Cannot write source file .hello_h, cause: java.lang.UnsupportedOperationException
java.lang.UnsupportedOperationException
at jdk.jextract/com.sun.tools.jextract.JType$Function.getSourceSignature(JType.java:246)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactory.lambda$visitFunction$15(JavaSourceFactory.java:358)
at java.logging/java.util.logging.Logger.log(Logger.java:1050)
at jdk.jextract/com.sun.tools.jextract.Log.print(Log.java:110)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactory.visitFunction(JavaSourceFactory.java:358)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactoryExt.visitFunction(JavaSourceFactoryExt.java:120)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactoryExt.visitFunction(JavaSourceFactoryExt.java:50)
at jdk.jextract/com.sun.tools.jextract.tree.FunctionTree.accept(FunctionTree.java:50)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactory.generateDecl(JavaSourceFactory.java:371)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactory.generate(JavaSourceFactory.java:129)
at jdk.jextract/com.sun.tools.jextract.JavaSourceFactoryExt.generate(JavaSourceFactoryExt.java:75)
at jdk.jextract/com.sun.tools.jextract.JextractTool.generateHeader(JextractTool.java:87)
at jdk.jextract/com.sun.tools.jextract.JextractTool.lambda$processHeaders$1(JextractTool.java:78)
at java.base/java.util.HashMap.forEach(HashMap.java:1338)
at jdk.jextract/com.sun.tools.jextract.JextractTool.processHeaders(JextractTool.java:78)
at jdk.jextract/com.sun.tools.jextract.Main.runInternal(Main.java:293)
at jdk.jextract/com.sun.tools.jextract.Main.run(Main.java:211)
at jdk.jextract/com.sun.tools.jextract.Main.main(Main.java:352)
Tree causing above exception is: junk3