Merge pull request #1223 from ngzhian/1124

Handle offset references of the form [foo]:bar (fixes #1124)

src/ShellCheck/Analytics.hs

@@ -1820,6 +1820,7 @@ prop_checkUnused36= verifyNotTree checkUnusedAssignments "if [[ -v foo ]]; then
 prop_checkUnused37= verifyNotTree checkUnusedAssignments "fd=2; exec {fd}>&-"
 prop_checkUnused38= verifyTree checkUnusedAssignments "(( a=42 ))"
 prop_checkUnused39= verifyNotTree checkUnusedAssignments "declare -x -f foo"
+prop_checkUnused40= verifyNotTree checkUnusedAssignments "arr=(1 2); num=2; echo \"${arr[@]:num}\""
 checkUnusedAssignments params t = execWriter (mapM_ warnFor unused)
   where
     flow = variableFlow params

src/ShellCheck/AnalyzerLib.hs

@@ -622,12 +622,17 @@ getIndexReferences s = fromMaybe [] $ do
   where
     re = mkRegex "(\\[.*\\])"
 
+prop_getOffsetReferences1 = getOffsetReferences ":bar" == ["bar"]
+prop_getOffsetReferences2 = getOffsetReferences ":bar:baz" == ["bar", "baz"]
+prop_getOffsetReferences3 = getOffsetReferences "[foo]:bar" == ["bar"]
+prop_getOffsetReferences4 = getOffsetReferences "[foo]:bar:baz" == ["bar", "baz"]
 getOffsetReferences mods = fromMaybe [] $ do
+-- if mods start with [, then drop until ]
     match <- matchRegex re mods
-    offsets <- match !!! 0
+    offsets <- match !!! 1
     return $ matchAllStrings variableNameRegex offsets
   where
-    re = mkRegex "^ *:([^-=?+].*)"
+    re = mkRegex "^(\\[.+\\])? *:([^-=?+].*)"
 
 getReferencedVariables parents t =
     case t of