From 5c01b6c7f5f77380e24cd54f3e1494aa20351c0e Mon Sep 17 00:00:00 2001
From: Vidar Holen <spam@vidarholen.net>
Date: Sun, 16 Apr 2017 18:11:00 -0700
Subject: [PATCH] Parse empty [ ] conditionals

---
 ShellCheck/AST.hs       |  2 ++
 ShellCheck/Analytics.hs |  7 +++++++
 ShellCheck/Parser.hs    | 10 ++++++++--
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/ShellCheck/AST.hs b/ShellCheck/AST.hs
index 961a897..fec6247 100644
--- a/ShellCheck/AST.hs
+++ b/ShellCheck/AST.hs
@@ -48,6 +48,7 @@ data Token =
     | TC_Nullary Id ConditionType Token
     | TC_Or Id ConditionType String Token Token
     | TC_Unary Id ConditionType String Token
+    | TC_Empty Id ConditionType
     | T_AND_IF Id
     | T_AndIf Id Token Token
     | T_Arithmetic Id Token
@@ -372,6 +373,7 @@ getId t = case t of
         T_CoProcBody id _ -> id
         T_Include id _ _ -> id
         T_UnparsedIndex id _ _ -> id
+        TC_Empty id _ -> id
 
 blank :: Monad m => Token -> m ()
 blank = const $ return ()
diff --git a/ShellCheck/Analytics.hs b/ShellCheck/Analytics.hs
index 094e226..cf5f9f9 100644
--- a/ShellCheck/Analytics.hs
+++ b/ShellCheck/Analytics.hs
@@ -163,6 +163,7 @@ nodeChecks = [
     ,checkSplittingInArrays
     ,checkRedirectionToNumber
     ,checkGlobAsCommand
+    ,checkEmptyCondition
     ]
 
 
@@ -2819,5 +2820,11 @@ checkGlobAsCommand _ t = case t of
             warn (getId first) 2211 "This is a glob used as a command name. Was it supposed to be in ${..}, array, or is it missing quoting?"
     _ -> return ()
 
+prop_checkEmptyCondition1 = verify checkEmptyCondition "if [ ]; then ..; fi"
+prop_checkEmptyCondition2 = verifyNot checkEmptyCondition "[ foo -o bar ]"
+checkEmptyCondition _ t = case t of
+    TC_Empty id _ -> style id 2212 "Use 'false' instead of empty [/[[ conditionals."
+    _ -> return ()
+
 return []
 runTests =  $( [| $(forAllProperties) (quickCheckWithResult (stdArgs { maxSuccess = 1 }) ) |])
diff --git a/ShellCheck/Parser.hs b/ShellCheck/Parser.hs
index 9f1c2fa..ba0bcab 100644
--- a/ShellCheck/Parser.hs
+++ b/ShellCheck/Parser.hs
@@ -848,11 +848,13 @@ prop_readCondition14= isOk readCondition "[ foo '>' bar ]"
 prop_readCondition15= isOk readCondition "[ foo \">=\" bar ]"
 prop_readCondition16= isOk readCondition "[ foo \\< bar ]"
 prop_readCondition17= isOk readCondition "[[ ${file::1} = [-.\\|/\\\\] ]]"
+prop_readCondition18= isOk readCondition "[ ]"
 readCondition = called "test expression" $ do
     opos <- getPosition
     id <- getNextId
     open <- try (string "[[") <|> string "["
     let single = open == "["
+    let typ = if single then SingleBracket else DoubleBracket
 
     pos <- getPosition
     space <- allspacing
@@ -864,7 +866,11 @@ readCondition = called "test expression" $ do
     when (single && '\n' `elem` space) $
         parseProblemAt pos ErrorC 1080 "You need \\ before line feeds to break lines in [ ]."
 
-    condition <- readConditionContents single
+    condition <- readConditionContents single <|> do
+        guard . not . null $ space
+        lookAhead $ string "]"
+        id <- getNextIdAt pos
+        return $ TC_Empty id typ
 
     cpos <- getPosition
     close <- try (string "]]") <|> string "]" <|> fail "Expected test to end here (don't wrap commands in []/[[]])"
@@ -872,7 +878,7 @@ readCondition = called "test expression" $ do
     when (open == "[" && close /= "]" ) $ parseProblemAt opos ErrorC 1034 "Did you mean [[ ?"
     spacing
     many readCmdWord -- Read and throw away remainders to get then/do warnings. Fixme?
-    return $ T_Condition id (if single then SingleBracket else DoubleBracket) condition
+    return $ T_Condition id typ condition
 
 readAnnotationPrefix = do
     char '#'