Use the Identity monad to avoid unnecessary uses of fromJust

src/ShellCheck/ASTLib.hs

@@ -25,6 +25,7 @@ import Control.Monad.Writer
 import Control.Monad
 import Data.Char
 import Data.Functor
+import Data.Functor.Identity
 import Data.List
 import Data.Maybe
 
@@ -177,7 +178,7 @@ getLiteralString = getLiteralStringExt (const Nothing)
 
 -- Definitely get a literal string, skipping over all non-literals
 onlyLiteralString :: Token -> String
-onlyLiteralString = fromJust . getLiteralStringExt (const $ return "")
+onlyLiteralString = runIdentity . getLiteralStringExt (const $ return "")
 
 -- Maybe get a literal string, but only if it's an unquoted argument.
 getUnquotedLiteral (T_NormalWord _ list) =
@@ -216,7 +217,7 @@ getGlobOrLiteralString = getLiteralStringExt f
 
 -- Maybe get the literal value of a token, using a custom function
 -- to map unrecognized Tokens into strings.
-getLiteralStringExt :: (Token -> Maybe String) -> Token -> Maybe String
+getLiteralStringExt :: Monad m => (Token -> m String) -> Token -> m String
 getLiteralStringExt more = g
   where
     allInList = fmap concat . mapM g

src/ShellCheck/AnalyzerLib.hs

@@ -806,7 +806,7 @@ isVariableName (x:r) = isVariableStartChar x && all isVariableChar r
 isVariableName _     = False
 
 getVariablesFromLiteralToken token =
-    getVariablesFromLiteral (fromJust $ getLiteralStringExt (const $ return " ") token)
+    getVariablesFromLiteral (runIdentity $ getLiteralStringExt (const $ return " ") token)
 
 -- Try to get referenced variables from a literal string like "$foo"
 -- Ignores tons of cases like arithmetic evaluation and array indices.

src/ShellCheck/Checks/Commands.hs

@@ -34,6 +34,7 @@ import ShellCheck.Regex
 import Control.Monad
 import Control.Monad.RWS
 import Data.Char
+import Data.Functor.Identity
 import Data.List
 import Data.Maybe
 import qualified Data.Map.Strict as Map
@@ -348,7 +349,7 @@ returnOrExit multi invalid = (f . arguments)
     isInvalid s = null s || any (not . isDigit) s || length s > 5
         || let value = (read s :: Integer) in value > 255
 
-    literal token = fromJust $ getLiteralStringExt lit token
+    literal token = runIdentity $ getLiteralStringExt lit token
     lit (T_DollarBraced {}) = return "0"
     lit (T_DollarArithmetic {}) = return "0"
     lit (T_DollarExpansion {}) = return "0"
@@ -735,7 +736,7 @@ checkAliasesUsesArgs = CommandCheck (Exactly "alias") (f . arguments)
     re = mkRegex "\\$\\{?[0-9*@]"
     f = mapM_ checkArg
     checkArg arg =
-        let string = fromJust $ getLiteralStringExt (const $ return "_") arg in
+        let string = runIdentity $ getLiteralStringExt (const $ return "_") arg in
             when ('=' `elem` string && string `matches` re) $
                 err (getId arg) 2142
                     "Aliases can't use positional parameters. Use a function."
@@ -781,7 +782,7 @@ checkFindWithoutPath = CommandCheck (Basename "find") f
     -- path. We assume that all the pre-path flags are single characters from a
     -- list of GNU and macOS flags.
     hasPath (first:rest) =
-        let flag = fromJust $ getLiteralStringExt (const $ return "___") first in
+        let flag = runIdentity $ getLiteralStringExt (const $ return "___") first in
             not ("-" `isPrefixOf` flag) || isLeadingFlag flag && hasPath rest
     hasPath [] = False
     isLeadingFlag flag = length flag <= 2 || all (`elem` leadingFlagChars) flag

src/ShellCheck/Checks/ShellSupport.hs

@@ -30,6 +30,7 @@ import ShellCheck.Regex
 import Control.Monad
 import Control.Monad.RWS
 import Data.Char
+import Data.Functor.Identity
 import Data.List
 import Data.Maybe
 import qualified Data.Map as Map
@@ -488,7 +489,7 @@ checkBraceExpansionVars = ForShell [Bash] f
             T_DollarExpansion {} -> return "$"
             T_DollarArithmetic {} -> return "$"
             _ -> return "-"
-    toString t = fromJust $ getLiteralStringExt literalExt t
+    toString t = runIdentity $ getLiteralStringExt literalExt t
     isEvaled t = do
         cmd <- getClosestCommandM t
         return $ maybe False (`isUnqualifiedCommand` "eval") cmd