[makeotfexe] ignore rsub is resolved to ignore sub

[khaledhosny]

Not sure if this intentional or not, but ignore rsub produces the same lookup as ignore sub. The following two lookups:

lookup test {                                                                   
 ignore rsub A [B];                                                             
} test;

lookup test {                                                                   
 ignore sub A [B];                                                             
} test;

Produce:

  <GSUB>                                                                        
    <Version value="0x00010000"/>                                               
    <ScriptList>                                                                
      <!-- ScriptCount=0 -->                                                    
    </ScriptList>                                                               
    <FeatureList>                                                               
      <!-- FeatureCount=0 -->                                                   
    </FeatureList>                                                              
    <LookupList>                                                                
      <!-- LookupCount=1 -->                                                    
      <Lookup index="0">                                                        
        <LookupType value="6"/>                                                 
        <LookupFlag value="0"/>                                                 
        <!-- SubTableCount=1 -->                                                
        <ChainContextSubst index="0" Format="3">                                
          <!-- BacktrackGlyphCount=0 -->                                        
          <!-- InputGlyphCount=1 -->                                            
          <InputCoverage index="0" Format="1">                                  
            <Glyph value="A"/>                                                  
          </InputCoverage>                                                      
          <!-- LookAheadGlyphCount=1 -->                                        
          <LookAheadCoverage index="0" Format="1">                              
            <Glyph value="B"/>                                                  
          </LookAheadCoverage>                                                  
          <!-- SubstCount=0 -->                                                 
        </ChainContextSubst>                                                    
      </Lookup>                                                                 
    </LookupList>                                                               
  </GSUB>              

[readroberts]

Definitely a bug. The rsub should show a different lookup type.

[NorbertLindenberg]

In addition, when ignore rsub is used together with another rsub rule, this leads to weird behavior that’s hard to understand:

• If the two rules are inside a lookup block, makeotf reports a bug Error: "Lookup type different from previous rules in this lookup block" in Feature mark in line: xx. As usual with makeotf, xx is far far from the location of the code that it misunderstands.

• If the two rules are outside a lookup block, makeotf doesn’t complain, but quietly packages them in two separate lookups, thus defeating the purpose of the ignore rule.

[khaledhosny]

Both of these would be manifestations of the same root issue, since makeotf is effectively parsing ignore rsub as ignore sub which can’t be mixed with rsub in same lookup as there are different types.