Move mergeRanges to Lint.Fix

Also add tests and documentation

src/Lint/Fix.elm

@@ -1,6 +1,7 @@
 module Lint.Fix exposing
     ( Fix
     , removeRange, replaceRangeBy, insertAt
+    , mergeRanges
     , fix
     )
 
@@ -17,6 +18,11 @@ module Lint.Fix exposing
 @docs removeRange, replaceRangeBy, insertAt
 
 
+# Utilitaries for working with ranges
+
+@docs mergeRanges
+
+
 # Applying fixes
 
 @docs fix
@@ -95,6 +101,66 @@ rangePosition fix_ =
     row * 1000000 + column
 
 
+
+-- UTILITARIES FOR WORKING WITH RANGES
+
+
+{-| Create a new range that starts at the start of the range that starts first,
+and ends at the end of the range that starts last. If the two ranges are distinct
+and there is code in between, that code will be included in the resulting range.
+
+    range : Range
+    range =
+        Fix.mergeRanges
+            (Node.range node1)
+            (Node.range node2)
+
+-}
+mergeRanges : Range -> Range -> Range
+mergeRanges a b =
+    let
+        start : { row : Int, column : Int }
+        start =
+            case comparePosition a.start b.start of
+                LT ->
+                    a.start
+
+                EQ ->
+                    a.start
+
+                GT ->
+                    b.start
+
+        end : { row : Int, column : Int }
+        end =
+            case comparePosition a.end b.end of
+                LT ->
+                    b.end
+
+                EQ ->
+                    b.end
+
+                GT ->
+                    a.end
+    in
+    { start = start, end = end }
+
+
+comparePosition : { row : Int, column : Int } -> { row : Int, column : Int } -> Order
+comparePosition a b =
+    let
+        order : Order
+        order =
+            compare a.row b.row
+    in
+    case order of
+        EQ ->
+            compare a.column b.column
+
+        _ ->
+            order
+
+
 applyFix : Fix -> String -> String
 applyFix fix_ source =
     source

src/Lint/Rule/NoUnusedVariables.elm

@@ -621,28 +621,20 @@ registerFunction function context =
 
         functionRange : Range
         functionRange =
-            mergeRanges
-                (Node.range function.declaration)
-                (case function.signature of
-                    Just signature ->
-                        Node.range signature
+            case function.signature of
+                Just signature ->
+                    Fix.mergeRanges
+                        (Node.range function.declaration)
+                        (Node.range signature)
 
-                    Nothing ->
-                        Node.range function.declaration
-                )
+                Nothing ->
+                    Node.range function.declaration
     in
     context
         |> register (Variable functionRange) (Node.range declaration.name) (Node.value declaration.name)
         |> markUsedTypesAndModules namesUsedInSignature
 
 
-mergeRanges : Range -> Range -> Range
-mergeRanges r1 r2 =
-    -- TODO Inverse r1 and r2 if r2 comes before r1
-    -- TODO Move into a util file or something
-    { start = r1.start, end = r2.end }
-
-
 collectFromExposing : Exposing -> List ( VariableType, Range, String )
 collectFromExposing exposing_ =
     case exposing_ of

tests/FixTest.elm

@@ -0,0 +1,103 @@
+module FixTest exposing (all)
+
+import Elm.Syntax.Range exposing (Range)
+import Expect exposing (Expectation)
+import Lint.Fix as Fix
+import Test exposing (Test, describe, test)
+
+
+all : Test
+all =
+    describe "Fix"
+        [ mergeRangesTest
+        ]
+
+
+mergeRangesTest : Test
+mergeRangesTest =
+    describe "mergeRanges"
+        [ test "should take the start of the one before and the end of the one after if ranges are distinct" <|
+            \() ->
+                let
+                    a : Range
+                    a =
+                        { start = { row = 2, column = 10 }
+                        , end = { row = 2, column = 15 }
+                        }
+
+                    b : Range
+                    b =
+                        { start = { row = 20, column = 1 }
+                        , end = { row = 22, column = 5 }
+                        }
+
+                    expected : Range
+                    expected =
+                        { start = { row = 2, column = 10 }
+                        , end = { row = 22, column = 5 }
+                        }
+                in
+                Expect.all
+                    [ \() ->
+                        Fix.mergeRanges a b
+                            |> Expect.equal expected
+                    , \() ->
+                        Fix.mergeRanges b a
+                            |> Expect.equal expected
+                    ]
+                    ()
+        , test "should take the start of the one that starts first and the end of the one ends last if ranges are shared" <|
+            \() ->
+                let
+                    a : Range
+                    a =
+                        { start = { row = 2, column = 10 }
+                        , end = { row = 10, column = 15 }
+                        }
+
+                    b : Range
+                    b =
+                        { start = { row = 5, column = 1 }
+                        , end = { row = 22, column = 5 }
+                        }
+
+                    expected : Range
+                    expected =
+                        { start = { row = 2, column = 10 }
+                        , end = { row = 22, column = 5 }
+                        }
+                in
+                Expect.all
+                    [ \() ->
+                        Fix.mergeRanges a b
+                            |> Expect.equal expected
+                    , \() ->
+                        Fix.mergeRanges b a
+                            |> Expect.equal expected
+                    ]
+                    ()
+        , test "should take the bigger one if one is included in the other" <|
+            \() ->
+                let
+                    a : Range
+                    a =
+                        { start = { row = 2, column = 10 }
+                        , end = { row = 10, column = 15 }
+                        }
+
+                    b : Range
+                    b =
+                        { start = { row = 3, column = 1 }
+                        , end = { row = 4, column = 5 }
+                        }
+                in
+                Expect.all
+                    [ \() ->
+                        Fix.mergeRanges a b
+                            |> Expect.equal a
+                    , \() ->
+                        Fix.mergeRanges b a
+                            |> Expect.equal a
+                    ]
+                    ()
+        ]