Go 1.21.0 was released in August 2023, so our upcoming release
will no longer support the Go 1.20 release series.
The first Go 1.22 release candidate is also due in December 2023,
less than a month from now, so dropping 1.20 will simplify 1.22 work.
The first makes our test scripts more consistent, as all external
program executions happen via "exec" and are not as easily confused
with custom builtin commands like our "generate-literals".
The second catches mistakes if any of our txtar files have duplicate
files, where all but one of the contents would be ignored before.
We can drop the code that kicked in when GOGARBLE was empty.
We can also add the value in addGarbleToHash unconditionally,
as we never allow it to be empty.
In the tests, remove all GOGARBLE lines where it just meant "obfuscate
everything" or "obfuscate the entire main module".
cgo.txtar had "obfuscate everything" as a separate step,
so remove it entirely.
linkname.txtar started failing because the imported package did not
import strings, so listPackage errored out. This wasn't a problem when
strings itself wasn't obfuscated, as transformLinkname silently left
strings.IndexByte untouched. It is a problem when IndexByte does get
obfuscated. Make that kind of listPackage error visible, and fix it.
reflect.txtar started failing with "unreachable method" runtime throws.
It's not clear to me why; it appears that GOGARBLE=* makes the linker
think that ExportedMethodName is suddenly unreachable.
Work around the problem by making the method explicitly reachable,
and leave a TODO as a reminder to investigate.
Finally, gogarble.txtar no longer needs to test for GOPRIVATE.
The rest of the test is left the same, as we still want the various
values for GOGARBLE to continue to work just like before.
Fixes#594.
Following the best practices from upstream.
In particular, the "txt" extension is somewhat ambiguous.
This may cause some conflicts due to the git diff noise,
but hopefully we won't ever do this again.
Daniel Martí