[ragel-users] "declared but not used" errors with v7 Go backend

[Adrian Thurston]

Hi Damian, 

I just altered the codegen so that unused arrays are not generated. This
eliminates the need to assign to _ for the static arrays. The need is
still there for static variables, for example: 

 _ = scanner_first_final
 _ = scanner_error
 _ = scanner_en_main

I've noticed though that the _ assignment trick isn't valid for arrays
that are not in a function scope, which means we can't use it right
after declaration. It could go into the write exec block or the write
init block though. To do that I'll have to create a dedicated reference
statement for the intermediate language since the go code generator does
not understand the state machine. It's just a language translation. The
reference statement can have no effect in other languages. 

For the time being I'll need to revert the _ assignment since it breaks
ragel programs where the data is not function scoped. 

Adrian 

On 2018-11-01 09:12, Damian Gryski wrote: 

> This is with ragel 7.0.0.11 and colm 0.13.0.6. I was unable to get ragel to build from git. 
> 
> With the example grammar at github.com/dgryski/ragel-examples/regexp1 [2], I get the following error: 
> 
> $ ragel-go sshd.rl 
> $ go build 
> # github.com/dgryski/ragel-examples/regexp1 [2] 
> ./sshd.go:11:6: _scanner_trans_cond_spaces declared and not used 
> ./sshd.go:12:6: _scanner_trans_offsets declared and not used 
> ./sshd.go:13:6: _scanner_trans_lengths declared and not used 
> ./sshd.go:14:6: _scanner_cond_keys declared and not used 
> ./sshd.go:17:6: _scanner_eof_cond_spaces declared and not used 
> ./sshd.go:18:6: _scanner_eof_cond_key_offs declared and not used 
> ./sshd.go:19:6: _scanner_eof_cond_key_lens declared and not used 
> ./sshd.go:20:6: _scanner_eof_cond_keys declared and not used 
> ./sshd.go:21:6: _scanner_nfa_targs declared and not used 
> ./sshd.go:22:6: _scanner_nfa_offsets declared and not used 
> ./sshd.go:22:6: too many errors 
> 
> The usual solution to this in autogenerated code is to assign them to `_`, the underscore "blank variable". This satisfies the compiler and the entire array will be eliminated as a dead-store if it ends up not being used. 
> 
> Thus, each declaration for variables which may or may not be used will look like: 
> var _scanner_trans_cond_spaces [] int8 = [] int8 { ... } 
> _ = _scanner_trans_cond_space 
> 
> Note also the first `[] int8` is redundant -- the compiler will infer the type from the type of the array on the right hand side of the `=`. 
> 
> Fixing these issues in the Go template in the src/host-go directory and rebuilding fixed these errors (although I had to copy files from the git checkout for the template changes to recompile successfully). 
> 
> Damian 
> 
> _______________________________________________
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> ragel-users at colm.net
> http://www.colm.net/cgi-bin/mailman/listinfo/ragel-users [1]
 

Links:
------
[1] http://www.colm.net/cgi-bin/mailman/listinfo/ragel-users
[2] http://github.com/dgryski/ragel-examples/regexp1
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