Googletest export

Fix Theta(N^2) memory usage of EXPECT_EQ(string) when the strings don't match.

The underlying CalculateOptimalEdits() implementation used a simple
dynamic-programming approach that always used N^2 memory and time. This meant
that tests for equality of large strings were ticking time bombs: They'd work
fine as long as the test passed, but as soon as the strings differed the test
would OOM, which is very hard to debug.
I switched it out for a Dijkstra search, which is still worst-case O(N^2), but
in the usual case of mostly-matching strings, it is much closer to linear.

PiperOrigin-RevId: 210405025

googletest/include/gtest/internal/gtest-internal.h

@@ -159,15 +159,15 @@ GTEST_DISABLE_MSC_WARNINGS_POP_()  //  4275
 
 #endif  // GTEST_HAS_EXCEPTIONS
 
-namespace edit_distance {
 // Returns the optimal edits to go from 'left' to 'right'.
 // All edits cost the same, with replace having lower priority than
-// add/remove.
-// Simple implementation of the Wagner-Fischer algorithm.
-// See http://en.wikipedia.org/wiki/Wagner-Fischer_algorithm
-enum EditType { kMatch, kAdd, kRemove, kReplace };
+// add/remove. Returns an approximation of the maximum memory used in
+// 'memory_usage' if non-null.
+// Uses a Dijkstra search, with a couple of simple bells and whistles added on.
+enum EditType { kEditMatch, kEditAdd, kEditRemove, kEditReplace };
 GTEST_API_ std::vector<EditType> CalculateOptimalEdits(
-    const std::vector<size_t>& left, const std::vector<size_t>& right);
+    const std::vector<size_t>& left, const std::vector<size_t>& right,
+    size_t* memory_usage = NULL);
 
 // Same as above, but the input is represented as strings.
 GTEST_API_ std::vector<EditType> CalculateOptimalEdits(
@@ -179,8 +179,6 @@ GTEST_API_ std::string CreateUnifiedDiff(const std::vector<std::string>& left,
                                          const std::vector<std::string>& right,
                                          size_t context = 2);
 
-}  // namespace edit_distance
-
 // Calculate the diff between 'left' and 'right' and return it in unified diff
 // format.
 // If not null, stores in 'total_line_count' the total number of lines found