@dsnet @bradfitz @mvdan per owners.

I think the root case of the issue is the function below:

func (s *scanner) eof() int {
	if s.err != nil {
		return scanError
	}
	if s.endTop {
		return scanEnd
	}
	s.step(s, ' ')
	if s.endTop {
		return scanEnd
	}
	if s.err == nil {
		s.err = &SyntaxError{"unexpected end of JSON input", s.bytes}
	}
	return scanError
}

I do update s.err == nil to be s.err != nil but causes some test cases to fail

A similar error in the past: #56332

There are a handful of these "confusing error message" bug reports on encoding/json. My intuition is that we shouldn't try to fix each one of them individually. cc @dsnet

I have an experimental CL in progress that completely switches the "encoding/json" parser to a new implementation, which will fix most (if not all) of these weird error cases.

I guess I should mention that I'm finding these issues by fuzzing my own JSON parser against encoding/json. My implementation is GPL, but I'm 100% willing to re-license it for incorporation in to the stdlib if there's anything that you'd like to steal.

In particular, compat/json/compat_test.go is some tests that may be worth stealing; they are tests that I felt necessary to add even though my implementation already passed encoding/json's existing test suite (which I have copied in the borrowed_*_test.go files).