This was reported in jextract-dev

https://mail.openjdk.org/pipermail/jextract-dev/2024-July/001843.html

boolean.h from the email is as follows:

typedef enum
{
    Boolean
} MyTypes;

jextracted file results in compilation error:

$ javac boolean_h.java
boolean_h.java:20: error: illegal forward reference
    static final boolean TRACE_DOWNCALLS = Boolean.getBoolean("jextract.trace.downcalls");
                                           ^
boolean_h.java:20: error: int cannot be dereferenced
    static final boolean TRACE_DOWNCALLS = Boolean.getBoolean("jextract.trace.downcalls");
                                                  ^
2 errors