tokenizer: skip lines that are just whitespace

src/blib2to3/pgen2/tokenize.py

@@ -608,6 +608,12 @@ def generate_tokens(
         except StopIteration:
             line = ""
         lnum += 1
+
+        # skip lines that are just a slash, to avoid storing that line's
+        # indent information.
+        if line.rstrip("\n").strip(" \t") == "\\":
+            continue
+
         pos, max = 0, len(line)
 
         if contstr:  # continued string

tests/data/cases/backslash_before_indent.py

@@ -0,0 +1,18 @@
+class Plotter:
+\
+    pass
+
+class AnotherCase:
+  \
+    pass
+
+# output
+
+class Plotter:
+
+    pass
+
+
+class AnotherCase:
+
+    pass