Improve warnings for bad parameter expansion (fixes #2297)

CHANGELOG.md

@@ -6,6 +6,7 @@
 - SC2292: Suggest [[ over [ in Bash/Ksh scripts (optional)
 - SC2293/SC2294: Warn when calling `eval` with arrays
 - SC2295: Warn about "${x#$y}" treating $y as a pattern when not quoted
+- SC2296-SC2301: Improved warnings for bad parameter expansions
 
 ### Fixed
 - SC2102 about repetitions in ranges no longer triggers on [[ -v arr[xx] ]]

src/ShellCheck/Analytics.hs

@@ -136,7 +136,7 @@ nodeChecks = [
     ,checkValidCondOps
     ,checkGlobbedRegex
     ,checkTestRedirects
-    ,checkIndirectExpansion
+    ,checkBadParameterSubstitution
     ,checkPS1Assignments
     ,checkBackticks
     ,checkInexplicablyUnquoted
@@ -1608,29 +1608,79 @@ checkBackticks params (T_Backticked id list) | not (null list) =
             (fixWith [replaceStart id params 1 "$(", replaceEnd id params 1 ")"])
 checkBackticks _ _ = return ()
 
-prop_checkIndirectExpansion1 = verify checkIndirectExpansion "${foo$n}"
+
-prop_checkIndirectExpansion2 = verifyNot checkIndirectExpansion "${foo//$n/lol}"
+prop_checkBadParameterSubstitution1 = verify checkBadParameterSubstitution "${foo$n}"
-prop_checkIndirectExpansion3 = verify checkIndirectExpansion "${$#}"
+prop_checkBadParameterSubstitution2 = verifyNot checkBadParameterSubstitution "${foo//$n/lol}"
-prop_checkIndirectExpansion4 = verify checkIndirectExpansion "${var${n}_$((i%2))}"
+prop_checkBadParameterSubstitution3 = verify checkBadParameterSubstitution "${$#}"
-prop_checkIndirectExpansion5 = verifyNot checkIndirectExpansion "${bar}"
+prop_checkBadParameterSubstitution4 = verify checkBadParameterSubstitution "${var${n}_$((i%2))}"
-checkIndirectExpansion _ (T_DollarBraced i _ (T_NormalWord _ contents))
+prop_checkBadParameterSubstitution5 = verifyNot checkBadParameterSubstitution "${bar}"
-    | isIndirection contents =
+prop_checkBadParameterSubstitution6 = verify checkBadParameterSubstitution "${\"bar\"}"
-        err i 2082 "To expand via indirection, use arrays, ${!name} or (for sh only) eval."
+prop_checkBadParameterSubstitution7 = verify checkBadParameterSubstitution "${{var}"
+prop_checkBadParameterSubstitution8 = verify checkBadParameterSubstitution "${$(x)//x/y}"
+prop_checkBadParameterSubstitution9 = verifyNot checkBadParameterSubstitution "$# ${#} $! ${!} ${!#} ${#!}"
+prop_checkBadParameterSubstitution10 = verify checkBadParameterSubstitution "${'foo'}"
+prop_checkBadParameterSubstitution11 = verify checkBadParameterSubstitution "${${x%.*}##*/}"
+
+checkBadParameterSubstitution _ t =
+    case t of
+        (T_DollarBraced i _ (T_NormalWord _ contents@(first:_))) ->
+            if isIndirection contents
+            then err i 2082 "To expand via indirection, use arrays, ${!name} or (for sh only) eval."
+            else checkFirst first
+        _ -> return ()
+
   where
+
     isIndirection vars =
         let list = mapMaybe isIndirectionPart vars in
             not (null list) && and list
+
     isIndirectionPart t =
-        case t of T_DollarExpansion _ _ ->  Just True
+        case t of T_DollarExpansion {} ->  Just True
-                  T_Backticked _ _ ->       Just True
+                  T_Backticked {} ->       Just True
-                  T_DollarBraced _ _ _ ->     Just True
+                  T_DollarBraced {} ->     Just True
-                  T_DollarArithmetic _ _ -> Just True
+                  T_DollarArithmetic {} -> Just True
                   T_Literal _ s -> if all isVariableChar s
                                     then Nothing
                                     else Just False
                   _ -> Just False
 
-checkIndirectExpansion _ _ = return ()
+    checkFirst t =
+        case t of
+            T_Literal id (c:_) ->
+                if isVariableChar c || isSpecialVariableChar c
+                then return ()
+                else err id 2296 $ "Parameter expansions can't start with " ++ e4m [c] ++ ". Double check syntax."
+
+            T_ParamSubSpecialChar {} -> return ()
+
+            T_DoubleQuoted id [T_Literal _ s] | isVariable s ->
+                err id 2297 "Double quotes must be outside ${}: ${\"invalid\"} vs \"${valid}\"."
+
+            T_DollarBraced id braces _ | isUnmodifiedParameterExpansion t ->
+                err id 2298 $
+                    (if braces then "${${x}}" else "${$x}")
+                      ++ " is invalid. For expansion, use ${x}. For indirection, use arrays, ${!x} or (for sh) eval."
+
+            T_DollarBraced {} ->
+                err (getId t) 2299 "Parameter expansions can't be nested. Use temporary variables."
+
+            _ | isCommandSubstitution t ->
+                err (getId t) 2300 "Parameter expansion can't be applied to command substitutions. Use temporary variables."
+
+            _ -> err (getId t) 2301 $ "Parameter expansion starts with unexpected " ++ name t ++ ". Double check syntax."
+
+    isVariable str =
+        case str of
+            [c] -> isVariableStartChar c || isSpecialVariableChar c || isDigit c
+            x -> isVariableName x
+
+    name t =
+        case t of
+            T_SingleQuoted {} -> "quotes"
+            T_DoubleQuoted {} -> "quotes"
+            _ -> "syntax"
+
 
 prop_checkInexplicablyUnquoted1 = verify checkInexplicablyUnquoted "echo 'var='value';'"
 prop_checkInexplicablyUnquoted2 = verifyNot checkInexplicablyUnquoted "'foo'*"
@@ -4434,5 +4484,6 @@ checkUnquotedParameterExpansionPattern params x =
                 surroundWith (getId t) params "\""
 
 
+
 return []
 runTests =  $( [| $(forAllProperties) (quickCheckWithResult (stdArgs { maxSuccess = 1 }) ) |])

src/ShellCheck/AnalyzerLib.hs

@@ -816,6 +816,7 @@ isConfusedGlobRegex _       = False
 
 isVariableStartChar x = x == '_' || isAsciiLower x || isAsciiUpper x
 isVariableChar x = isVariableStartChar x || isDigit x
+isSpecialVariableChar = (`elem` "*@#?-$!")
 variableNameRegex = mkRegex "[_a-zA-Z][_a-zA-Z0-9]*"
 
 prop_isVariableName1 = isVariableName "_fo123"
@@ -861,7 +862,7 @@ getBracedReference s = fromMaybe s $
         let name = takeWhile isVariableChar s
         guard . not $ null name
         return name
-    getSpecial (c:_) | c `elem` "*@#?-$!" = return [c]
+    getSpecial (c:_) | isSpecialVariableChar c = return [c]
     getSpecial _ = fail "empty or not special"
 
     nameExpansion ('!':next:rest) = do -- e.g. ${!foo*bar*}
@@ -955,5 +956,17 @@ isBashLike params =
         Dash -> False
         Sh -> False
 
+-- Returns whether a token is a parameter expansion without any modifiers.
+-- True for $var ${var} $1 $#
+-- False for ${#var} ${var[x]} ${var:-0}
+isUnmodifiedParameterExpansion t =
+    case t of
+        T_DollarBraced _ False _ -> True
+        T_DollarBraced _ _ list ->
+            let str = concat $ oversimplify list
+            in getBracedReference str == str
+        _ -> False
+
+
 return []
 runTests =  $( [| $(forAllProperties) (quickCheckWithResult (stdArgs { maxSuccess = 1 }) ) |])