fix: Clamp both of range's endpoints before subtracting

dataframe-operations/src/DataFrame/Operations/Subset.hs

@@ -176,12 +176,16 @@ dropLast n d =
 range :: (Int, Int) -> DataFrame -> DataFrame
 range (start, end) d =
     d
-        { columns = V.map (sliceColumn (clip start 0 r) n') (columns d)
+        { columns = V.map (sliceColumn start' n') (columns d)
         , dataframeDimensions = (n', c)
         }
   where
     (r, c) = dataframeDimensions d
-    n' = clip (end - start) 0 r
+    start' = clip start 0 r
+    -- Clamp both endpoints before subtracting: end - start' on an unclamped
+    -- end wraps for very negative values and reopens the range.
+    end' = clip end start' r
+    n' = end' - start'
 
 clip :: Int -> Int -> Int -> Int
 clip n left right = min right $ max n left

tests/Main.hs

@@ -143,6 +143,10 @@ main = do
                 mapM
                     (quickCheckWithResult stdArgs)
                     Operations.Subset.tests
+            subsetPropRes <-
+                mapM
+                    (quickCheckWithResult stdArgs)
+                    Operations.Subset.properties
             monadRes <- mapM (quickCheckWithResult stdArgs) Monad.tests
             cbRes <-
                 mapM
@@ -151,6 +155,7 @@ main = do
             propsRes <- mapM (quickCheckWithResult stdArgs) Properties.tests
             catRes <- mapM (quickCheckWithResult stdArgs) Properties.Categorical.tests
             if not (all isSuccessful propRes)
+                || not (all isSuccessful subsetPropRes)
                 || not (all isSuccessful cbRes)
                 || not (all isSuccessful monadRes)
                 || not (all isSuccessful propsRes)

tests/Operations/Subset.hs

@@ -9,8 +9,10 @@ import qualified DataFrame as D
 import qualified DataFrame.Internal.Column as Col
 import DataFrame.Internal.DataFrame
 import DataFrame.Operations.Merge ()
+import GenDataFrame ()
 import System.Random
 import Test.HUnit
+import Test.QuickCheck (Property, property)
 
 prop_dropZero :: DataFrame -> Bool
 prop_dropZero df = D.drop 0 df == df
@@ -53,6 +55,17 @@ prop_rangeFull df =
     let rows = fst (dataframeDimensions df)
      in D.range (0, rows) df == df
 
+prop_rangeClampsToBounds :: DataFrame -> Int -> Int -> Bool
+prop_rangeClampsToBounds df a b =
+    fst (dataframeDimensions (D.range (a, b) df)) == expected
+  where
+    rows = fst (dataframeDimensions df)
+    -- Rows in [a, b) that actually exist. Clamps before subtracting so the
+    -- oracle itself cannot overflow on extreme endpoints.
+    lo = min (max a 0) rows
+    hi = min (max b lo) rows
+    expected = hi - lo
+
 prop_selectAll :: DataFrame -> Bool
 prop_selectAll df = D.select (D.columnNames df) df == df
 
@@ -177,6 +190,37 @@ unit_stratifiedSplit_proportions =
                     )
                     (abs (vaProp - origProp) < tol)
 
+tenRows :: DataFrame
+tenRows = fromNamedColumns [("x", Col.fromList ([0 .. 9] :: [Int]))]
+
+-- Endpoints that overflow Int if the length is computed before clamping.
+unit_rangeExtremeEndpoints :: Test
+unit_rangeExtremeEndpoints =
+    TestCase
+        ( assertEqual
+            "range (1, minBound) is empty, not a wrapped-around full range"
+            0
+            (fst (dataframeDimensions (D.range (1, minBound) tenRows)))
+        )
+
+unit_rangeEndPastEnd :: Test
+unit_rangeEndPastEnd =
+    TestCase
+        ( assertEqual
+            "range (8, 20) on a 10-row frame yields rows 8 and 9"
+            (Just (Col.fromList ([8, 9] :: [Int])))
+            (getColumn "x" (D.range (8, 20) tenRows))
+        )
+
+unit_rangeStartBeforeZero :: Test
+unit_rangeStartBeforeZero =
+    TestCase
+        ( assertEqual
+            "range (-5, 3) on a 10-row frame yields rows 0 to 2"
+            (Just (Col.fromList ([0, 1, 2] :: [Int])))
+            (getColumn "x" (D.range (-5, 3) tenRows))
+        )
+
 hunitTests :: [Test]
 hunitTests =
     [ TestLabel "unit_stratifiedSample_full" unit_stratifiedSample_full
@@ -185,8 +229,15 @@ hunitTests =
         "unit_stratifiedSplit_singleRowStratum"
         unit_stratifiedSplit_singleRowStratum
     , TestLabel "unit_stratifiedSplit_proportions" unit_stratifiedSplit_proportions
+    , TestLabel "unit_rangeEndPastEnd" unit_rangeEndPastEnd
+    , TestLabel "unit_rangeExtremeEndpoints" unit_rangeExtremeEndpoints
+    , TestLabel "unit_rangeStartBeforeZero" unit_rangeStartBeforeZero
     ]
 
+-- Properties whose shape does not fit [DataFrame -> Bool].
+properties :: [Property]
+properties = [property prop_rangeClampsToBounds]
+
 tests :: [DataFrame -> Bool]
 tests =
     [ prop_dropZero