Don't trigger SC2154 (unassigned var) in `-n`/`-z` expressions #1583

src/ShellCheck/Analytics.hs

@@ -2191,6 +2191,16 @@ prop_checkUnassignedReferences37= verifyNotTree checkUnassignedReferences "var=h
 prop_checkUnassignedReferences38= verifyTree (checkUnassignedReferences' True) "echo $VAR"
 prop_checkUnassignedReferences39= verifyNotTree checkUnassignedReferences "builtin export var=4; echo $var"
 
+prop_checkUnassignedReferences_minusNPlain   = verifyNotTree checkUnassignedReferences "if [ -n \"$x\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZPlain   = verifyNotTree checkUnassignedReferences "if [ -z \"$x\" ]; then echo \"\"; fi"
+prop_checkUnassignedReferences_minusNBraced  = verifyNotTree checkUnassignedReferences "if [ -n \"${x}\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZBraced  = verifyNotTree checkUnassignedReferences "if [ -z \"${x}\" ]; then echo \"\"; fi"
+prop_checkUnassignedReferences_minusNDefault = verifyNotTree checkUnassignedReferences "if [ -n \"${x:-}\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZDefault = verifyNotTree checkUnassignedReferences "if [ -z \"${x:-}\" ]; then echo \"\"; fi"
+
+prop_checkUnassignedReferences_minusZInsteadOfN       = verifyTree checkUnassignedReferences "if [ -z \"$x\" ]; then echo $x; fi"
+prop_checkUnassignedReferences_minusZInsteadOfNBraced = verifyTree checkUnassignedReferences "if [ -z \"${x}\" ]; then echo $x; fi"
+
 checkUnassignedReferences = checkUnassignedReferences' False
 checkUnassignedReferences' includeGlobals params t = warnings
   where

src/ShellCheck/AnalyzerLib.hs

@@ -510,6 +510,9 @@ getModifiedVariables t =
             guard . not . null $ str
             return (t, token, str, DataString SourceChecked)
 
+        TC_Unary _ _ "-n" (T_NormalWord _ [T_DoubleQuoted _ [db@(T_DollarBraced _ _ _)]]) ->
+            [(t, t, getBracedReference (bracedString db), DataString SourceChecked)]
+
         T_DollarBraced _ _ l -> maybeToList $ do
             let string = bracedString t
             let modifier = getBracedModifier string
@@ -719,7 +722,9 @@ getOffsetReferences mods = fromMaybe [] $ do
 getReferencedVariables parents t =
     case t of
         T_DollarBraced id _ l -> let str = bracedString t in
-            (t, t, getBracedReference str) :
+            if isMinusZTest t
+            then []
+            else (t, t, getBracedReference str) :
                 map (\x -> (l, l, x)) (
                     getIndexReferences str
                     ++ getOffsetReferences (getBracedModifier str))
@@ -774,6 +779,10 @@ getReferencedVariables parents t =
         this: TA_Assignment _ "=" lhs _ :_ -> lhs == t
         _                                  -> False
 
+    isMinusZTest t = case getPath parents t of
+        _ : T_DoubleQuoted _ [_] : T_NormalWord _ [_] : TC_Unary _ SingleBracket "-z" _ : _ -> True
+        _ -> False
+
 dataTypeFrom defaultType v = (case v of T_Array {} -> DataArray; _ -> defaultType) $ SourceFrom [v]