Treat compgen -V as assigning to an array

compgen -V arr (bash 5.3) stores the completions in the array arr instead of
printing them, but getModifiedVariableCommand did not know about it, so
`compgen -V files -G '*'` followed by "${files[@]}" produced a spurious
SC2154 "files is referenced but not assigned".

Add a compgen entry next to mapfile/readarray and a helper shaped like the
existing getPrintfVariable/getWaitVariable: parse the flags, take the argument
of -V and record it as DataArray.

Fixes #3466

Author: Eljees

src/ShellCheck/Analytics.hs

@@ -2534,6 +2534,8 @@ prop_checkUnassignedReferences50 = verifyNotTree checkUnassignedReferences "echo
 prop_checkUnassignedReferences51 = verifyNotTree checkUnassignedReferences "echo ${foo:+$foo}"
 prop_checkUnassignedReferences52 = verifyNotTree checkUnassignedReferences "wait -p pid; echo $pid"
 prop_checkUnassignedReferences53 = verifyTree checkUnassignedReferences "x=($foo)"
+prop_checkUnassignedReferences54 = verifyNotTree checkUnassignedReferences "compgen -V files -G '*'; echo \"${files[@]}\""
+prop_checkUnassignedReferences55 = verifyNotTree checkUnassignedReferences "compgen -A function -V funcs; echo \"${funcs[@]}\""
 
 checkUnassignedReferences = checkUnassignedReferences' False
 checkUnassignedReferences' includeGlobals params t = warnings

src/ShellCheck/AnalyzerLib.hs

@@ -683,6 +683,7 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
 
         "mapfile" -> maybeToList $ getMapfileArray base rest
         "readarray" -> maybeToList $ getMapfileArray base rest
+        "compgen" -> maybeToList $ getCompgenArray rest
 
         "DEFINE_boolean" -> maybeToList $ getFlagVariable rest
         "DEFINE_float" -> maybeToList $ getFlagVariable rest
@@ -742,6 +743,14 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
     getPrintfVariable list = getFlagAssignedVariable "v" (SourceFrom list) $ getBsdOpts "v:" list
     getWaitVariable   list = getFlagAssignedVariable "p" SourceInteger     $ return $ getGenericOpts list
 
+    -- compgen -V arr stores the completions in the array arr rather than printing them
+    getCompgenArray list = do
+        flags <- getGnuOpts "abcdefgjksuvo:A:C:F:G:P:S:V:W:X:" list
+        (_, (_, value)) <- find ((== "V") . fst) flags
+        name <- getLiteralString value
+        guard $ isVariableName name
+        return (base, value, name, DataArray SourceExternal)
+
     getFlagAssignedVariable str dataSource maybeFlags = do
         flags <- maybeFlags
         (_, (flag, value)) <- find ((== str) . fst) flags