`missed-obfuscation` incorrectly counts receiver `ρ` as a void leading to spurious defect reports

What happens

missed-obfuscation counts the receiver ρ among the void attributes a formation is told to obfuscate. A formation whose only void is its own receiver gets a defect it cannot act on, because ρ is the receiver and there is nothing to rename it to.

On lints de102d68 with eo-parser 0.63.0:

+package foo
+version 0.0.0

[^] > thing
  ^.other > @

void: name=[ρ]   (U+03C1)
DEFECT line 4: The formation "thing" must obfuscate its void attributes before decorating another object

A formation with a real void gets the same message, which is the intended case:

[x] > thing
  x > @

and one with no voids at all is silent, as it should be.

Over eo-runtime/src/main/eo (objectionary/eo at 8655f8755e) the rule reports 706 defects, and in 92 of them the only void of the formation is ρ.

Why

The selector takes any void whose name is not prefixed cant- (design/missed-obfuscation.xsl):

<xsl:for-each select="//o[eo:abstract(.) and @name and o[@name='φ'] and o[@base='∅' and @name and not(starts-with(@name, 'cant-'))]]">

Writing the receiver down as [^] emits <o base="∅" name="ρ"/>, which matches. The motive talks only about attributes a caller provides:

A formation that decorates another object should obfuscate its void attributes. Otherwise, an attribute of the formation may shadow an attribute with the same name in the decoratee

ρ shadows nothing of the kind: it is the receiver every formation has, and eo-printer writes it as ^ rather than as a name a reader could confuse with an attribute of the decoratee.

This is the same shape as #1299, where many-void-attributes counts ρ against its cap of five. The fix there is the fix here.

How to fix

Leave the receiver out of the selector:

<xsl:for-each select="//o[eo:abstract(.) and @name and o[@name='φ'] and o[@base='∅' and @name and @name != 'ρ' and not(starts-with(@name, 'cant-'))]]">

A pack for it: [^] > thing with ^.other > @ must give defects: 0, while [^ x] > thing must still be reported for x.

Start in design/missed-obfuscation.xsl by reading the selector for void attributes and compare it with the handling described for #1299. Add or update a pack covering [^] > thing and [^ x] > thing; done means the receiver-only case reports zero defects while the real void x remains reported.