Add handling for special characters in parameter substitutions.

Fixes koalaman/shellcheck#562. Special characters inside braces are
parsed into T_ParamSubSpecialChar instead of T_Literal so that they are
not flagged in the function checkInexplicablyUnquoted when sandwiched
between double quotes.

ShellCheck/AST.hs

@@ -111,6 +111,7 @@ data Token =
     | T_NormalWord Id [Token]
     | T_OR_IF Id
     | T_OrIf Id (Token) (Token)
+    | T_ParamSubSpecialChar Id -- e.g. '%' in ${foo%bar}  or '/' in ${foo/bar/baz}
     | T_Pipeline Id [Token] [Token] -- [Pipe separators] [Commands]
     | T_ProcSub Id String [Token]
     | T_Rbrace Id
@@ -319,6 +320,7 @@ getId t = case t of
         T_DollarBraced id _  -> id
         T_DollarArithmetic id _  -> id
         T_BraceExpansion id _  -> id
+        T_ParamSubSpecialChar id -> id
         T_DollarBraceCommandExpansion id _  -> id
         T_IoFile id _ _  -> id
         T_IoDuplicate id _ _  -> id

ShellCheck/Analytics.hs

@@ -1324,6 +1324,7 @@ prop_checkInexplicablyUnquoted3 = verifyNot checkInexplicablyUnquoted "wget --us
 prop_checkInexplicablyUnquoted4 = verify checkInexplicablyUnquoted "echo \"VALUES (\"id\")\""
 prop_checkInexplicablyUnquoted5 = verifyNot checkInexplicablyUnquoted "\"$dir\"/\"$file\""
 prop_checkInexplicablyUnquoted6 = verifyNot checkInexplicablyUnquoted "\"$dir\"some_stuff\"$file\""
+prop_checkInexplicablyUnquoted7 = verifyNot checkInexplicablyUnquoted "${dir/\"foo\"/\"bar\"}"
 checkInexplicablyUnquoted _ (T_NormalWord id tokens) = mapM_ check (tails tokens)
   where
     check (T_SingleQuoted _ _:T_Literal id str:_)
@@ -1352,7 +1353,7 @@ checkInexplicablyUnquoted _ (T_NormalWord id tokens) = mapM_ check (tails tokens
     warnAboutExpansion id =
         warn id 2027 "The surrounding quotes actually unquote this. Remove or escape them."
     warnAboutLiteral id =
-        warn id 2140 "Word is on the form \"A\"B\"C\" (B indicated). Did you mean \"ABC\" or \"A\\\"B\\\"C\"?"
+        warn id 2140 "Word is of the form \"A\"B\"C\" (B indicated). Did you mean \"ABC\" or \"A\\\"B\\\"C\"?"
 checkInexplicablyUnquoted _ _ = return ()
 
 prop_checkTildeInQuotes1 = verify checkTildeInQuotes "var=\"~/out.txt\""

ShellCheck/Parser.hs

@@ -64,6 +64,7 @@ variableStart = upper <|> lower <|> oneOf "_"
 variableChars = upper <|> lower <|> digit <|> oneOf "_"
 functionChars = variableChars <|> oneOf ":+-.?"
 specialVariable = oneOf "@*#?-$!"
+paramSubSpecialChars = oneOf "/:+-=%"
 quotableChars = "|&;<>()\\ '\t\n\r\xA0" ++ doubleQuotableChars
 quotable = almostSpace <|> unicodeDoubleQuote <|> oneOf quotableChars
 bracedQuotable = oneOf "}\"$`'"
@@ -1003,13 +1004,20 @@ readDollarBracedWord = do
     list <- many readDollarBracedPart
     return $ T_NormalWord id list
 
-readDollarBracedPart = readSingleQuoted <|> readDoubleQuoted <|> readExtglob <|> readNormalDollar <|> readUnquotedBackTicked <|> readDollarBracedLiteral
+readDollarBracedPart = readSingleQuoted <|> readDoubleQuoted <|>
+                       readParamSubSpecialChar <|> readExtglob <|> readNormalDollar <|>
+                       readUnquotedBackTicked <|> readDollarBracedLiteral
 
 readDollarBracedLiteral = do
     id <- getNextId
     vars <- (readBraceEscaped <|> (anyChar >>= \x -> return [x])) `reluctantlyTill1` bracedQuotable
     return $ T_Literal id $ concat vars
 
+readParamSubSpecialChar = do
+    id <- getNextId
+    many1 paramSubSpecialChars
+    return $ T_ParamSubSpecialChar id
+
 prop_readProcSub1 = isOk readProcSub "<(echo test | wc -l)"
 prop_readProcSub2 = isOk readProcSub "<(  if true; then true; fi )"
 prop_readProcSub3 = isOk readProcSub "<( # nothing here \n)"