Avoid KeyError when imports are duplicated.

Because we do block splitting before deduplication, it could previously try to pop the same name twice.

Fixes facebook#194

setup.cfg

@@ -37,7 +37,7 @@ include = usort/*
 omit = usort/tests/*
 
 [coverage:report]
-fail_under = 70
+fail_under = 92
 precision = 1
 show_missing = True
 skip_covered = True

usort/sorting.py

@@ -163,7 +163,14 @@ def split_inplace(self, block: SortableBlock, overlap: Set[str]) -> SortableBloc
             # move imported names metadata
             for imp in new.imports:
                 for key in list(imp.imported_names):
-                    new.imported_names[key] = block.imported_names.pop(key)
+                    name = block.imported_names.pop(key, None)
+                    if name is not None:
+                        # Normally we wouldn't see multiple copies of a key because that
+                        # would have caused a block split already, but if an import is
+                        # just verbatim repeated, it's not technically shadowing.
+                        # If that's the case, we've already popped it and achieved the
+                        # goal of this block.
+                        new.imported_names[key] = name
 
         return new
 

usort/tests/__init__.py

@@ -6,6 +6,7 @@
 from .cli import CliTest
 from .config import ConfigTest
 from .functional import BasicOrderingTest, UsortStringFunctionalTest
+from .sorting import SplitTest
 from .stdlibs import StdlibsTest
 from .translate import IsSortableTest, SortableImportTest
 from .types import TypesTest
@@ -21,4 +22,5 @@
     "StdlibsTest",
     "TypesTest",
     "UtilTest",
+    "SplitTest",
 ]

usort/tests/functional.py

@@ -879,6 +879,21 @@ def test_sort_implicit_blocks3(self) -> None:
             """,
         )
 
+    def test_sort_merging_and_implicit_blocks(self) -> None:
+        self.assertUsortResult(
+            """
+                from a import x
+                from b import y
+                from b import y
+                from c import x
+            """,
+            """
+                from a import x
+                from b import y
+                from c import x
+            """,
+        )
+
     def test_skip_directives(self) -> None:
         """Test both usort:skip and isort:skip on single line imports"""
         self.assertUsortResult(