fix #4898 (#4899)

Author: zdenko

lib/coffeescript/lexer.js

@@ -478,7 +478,7 @@ exports.Lexer = class Lexer
 
     if size > @indent
       if noNewlines
-        @indebt = size - @indent
+        @indebt = size - @indent unless backslash
         @suppressNewlines()
         return indent.length
       unless @tokens.length

src/lexer.coffee

@@ -1287,3 +1287,56 @@ test "#4871: `else if` no longer output together ", ->
      2;
    }
    '''
+
+test "#4898: Lexer: backslash line continuation is inconsistent", ->
+  if ( \
+      false \
+      or \
+      true \
+    )
+    a = 42
+
+  eq a, 42
+
+  if ( \
+      false \
+      or \
+      true \
+  )
+    b = 42
+
+  eq b, 42
+
+  if ( \
+            false \
+         or \
+   true \
+  )
+    c = 42
+
+  eq c, 42
+
+  if \
+   false \
+        or \
+   true
+    d = 42
+
+  eq d, 42
+
+  if \
+              false or \
+  true
+    e = 42
+
+  eq e, 42
+
+  if \
+       false or \
+    true \
+       then \
+   f = 42 \
+   else
+     f = 24
+
+  eq f, 42