Add bindParameterIndex for working with named bound parameters

Add Database.SQLite3.Direct support for querying the index of a named
parameter in a statement.

Named parameters (e.g. 'SELECT :foo') allow for some convenient forms
of developing SQL queries that are harder to write and maintain with
positional arguments.

Database/SQLite3/Bindings.hs

@@ -30,6 +30,7 @@ module Database.SQLite3.Bindings (
     -- * Parameter and column information
     c_sqlite3_bind_parameter_count,
     c_sqlite3_bind_parameter_name,
+    c_sqlite3_bind_parameter_index,
     c_sqlite3_column_count,
     c_sqlite3_column_name,
 
@@ -198,6 +199,10 @@ foreign import ccall unsafe "sqlite3_bind_parameter_count"
 foreign import ccall unsafe "sqlite3_bind_parameter_name"
     c_sqlite3_bind_parameter_name :: Ptr CStatement -> CParamIndex -> IO CString
 
+-- | <http://www.sqlite.org/c3ref/bind_parameter_index.html>
+foreign import ccall unsafe "sqlite3_bind_parameter_index"
+    c_sqlite3_bind_parameter_index :: Ptr CStatement -> CString -> IO CParamIndex
+
 -- | <http://www.sqlite.org/c3ref/column_count.html>
 foreign import ccall unsafe "sqlite3_column_count"
     c_sqlite3_column_count :: Ptr CStatement -> IO CColumnCount

Database/SQLite3/Direct.hs

@@ -33,6 +33,7 @@ module Database.SQLite3.Direct (
     -- * Parameter and column information
     bindParameterCount,
     bindParameterName,
+    bindParameterIndex,
     columnCount,
     columnName,
 
@@ -406,6 +407,13 @@ bindParameterName (Statement stmt) idx =
     c_sqlite3_bind_parameter_name stmt (toFFI idx) >>=
         packUtf8 Nothing Just
 
+-- | <http://www.sqlite.org/c3ref/bind_parameter_index.html>
+bindParameterIndex :: Statement -> Utf8 -> IO (Maybe ParamIndex)
+bindParameterIndex (Statement stmt) (Utf8 name) =
+    BS.useAsCString name $ \name' -> do
+        idx <- fromFFI <$> c_sqlite3_bind_parameter_index stmt name'
+        return $ if idx == 0 then Nothing else Just idx
+
 -- | <http://www.sqlite.org/c3ref/column_count.html>
 columnCount :: Statement -> IO ColumnCount
 columnCount (Statement stmt) =

test/Main.hs

@@ -44,6 +44,7 @@ regressionTests =
     , TestLabel "Params"        . testBindParamCounts
     , TestLabel "Params"        . testBindParamName
     , TestLabel "Params"        . testBindErrorValidation
+    , TestLabel "Params"        . testNamedBindParams
     , TestLabel "Columns"       . testColumns
     , TestLabel "TypedColumns"  . testTypedColumns
     , TestLabel "ColumnName"    . testColumnName
@@ -302,6 +303,32 @@ testBindErrorValidation TestEnv{..} = TestCase $ do
     -- Invalid use, one param in q string, 2 given
     testException2 stmt = bind stmt [SQLInteger 1, SQLInteger 2]
 
+testNamedBindParams :: TestEnv -> Test
+testNamedBindParams TestEnv{..} = TestCase $ do
+  withConn $ \conn -> do
+    withStmt conn "SELECT :foo / :bar" $ \stmt -> do
+      -- Test that we get something back for known names
+      Just fooIdx <- Direct.bindParameterIndex stmt ":foo"
+      Just barIdx <- Direct.bindParameterIndex stmt ":bar"
+      -- Test that we get Nothing back for unknown names
+      Nothing <- Direct.bindParameterIndex stmt "intentionally_undefined"
+      Right () <- Direct.bindInt64 stmt fooIdx 4
+      Right () <- Direct.bindInt64 stmt barIdx 2
+      Row <- step stmt
+      1 <- columnCount stmt
+      [SQLInteger 2] <- columns stmt
+      Done <- step stmt
+      return ()
+    withStmt conn "SELECT @n1+@n2" $ \stmt -> do
+      -- Test that we get something back for known names
+      Just _n1 <- Direct.bindParameterIndex stmt "@n1"
+      Just _n2 <- Direct.bindParameterIndex stmt "@n2"
+      -- Here's where things get confusing..  You can't mix different
+      -- types of :/$/@ parameter conventions.
+      Nothing <- Direct.bindParameterIndex stmt ":n1"
+      Nothing <- Direct.bindParameterIndex stmt ":n2"
+      return ()
+
 testColumns :: TestEnv -> Test
 testColumns TestEnv{..} = TestCase $ do
   withConn $ \conn -> do