From a2cc44a04d45d6091cf9b9c3e4dea27ed8a8c177 Mon Sep 17 00:00:00 2001
From: Vidar Holen <spam@vidarholen.net>
Date: Thu, 15 Nov 2012 23:32:45 -0800
Subject: [PATCH] Added check for $(($n))

---
 ShellCheck/Analytics.hs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/ShellCheck/Analytics.hs b/ShellCheck/Analytics.hs
index b53e96f..8b0a1ca 100644
--- a/ShellCheck/Analytics.hs
+++ b/ShellCheck/Analytics.hs
@@ -37,6 +37,7 @@ basicChecks = [
     ,checkBraceExpansionVars
     ,checkForDecimals
     ,checkDivBeforeMult
+    ,checkArithmeticDeref
     ]
 
 modifyMap = modify
@@ -252,6 +253,13 @@ checkDivBeforeMult (TA_Binary _ "*" (TA_Binary id "/" _ _) _) = do
     addNoteFor id $ Note InfoC $ "Increase precision by replacing a/b*c with a*c/b"
 checkDivBeforeMult _ = return ()
 
+prop_checkArithmeticDeref = verify checkArithmeticDeref "echo $((3+$foo))"
+prop_checkArithmeticDeref2 = verify checkArithmeticDeref "cow=14; (( s+= $cow ))"
+prop_checkArithmeticDeref3 = verifyNot checkArithmeticDeref "cow=1/40; (( s+= ${cow%%/*} ))"
+checkArithmeticDeref (TA_Expansion _ (T_DollarBraced id str)) | not $ any (`elem` "/.:#%") $ str =
+    addNoteFor id $ Note WarningC $ "Don't use $ on variables in (( )) unless you want to dereference twice"
+checkArithmeticDeref _ = return ()
+
 allModifiedVariables t = snd $ runState (doAnalysis (\x -> modify $ (++) (getModifiedVariables x)) t) []
 
 --- Subshell detection