TripletSparseMatrix: guard against self-assignment

Change-Id: I63159b32d0462fe784019f17242cf4a9f05b2825

internal/ceres/triplet_sparse_matrix.cc

diff --git a/internal/ceres/triplet_sparse_matrix.cc b/internal/ceres/triplet_sparse_matrix.cc
index 15b9674..54b588b 100644
--- a/internal/ceres/triplet_sparse_matrix.cc
+++ b/internal/ceres/triplet_sparse_matrix.cc
@@ -97,6 +97,9 @@
 
 TripletSparseMatrix& TripletSparseMatrix::operator=(
     const TripletSparseMatrix& rhs) {
+  if (this == &rhs) {
+    return *this;
+  }
   num_rows_ = rhs.num_rows_;
   num_cols_ = rhs.num_cols_;
   num_nonzeros_ = rhs.num_nonzeros_;

internal/ceres/triplet_sparse_matrix_test.cc

diff --git a/internal/ceres/triplet_sparse_matrix_test.cc b/internal/ceres/triplet_sparse_matrix_test.cc
index d71df7b..881fabc 100644
--- a/internal/ceres/triplet_sparse_matrix_test.cc
+++ b/internal/ceres/triplet_sparse_matrix_test.cc
@@ -172,6 +172,35 @@
   EXPECT_DOUBLE_EQ(cpy.values()[1], 5.2);
 }
 
+TEST(TripletSparseMatrix, AssignmentOperatorSelfAssignment) {
+  TripletSparseMatrix orig(2, 5, 4);
+  orig.mutable_rows()[0] = 0;
+  orig.mutable_cols()[0] = 1;
+  orig.mutable_values()[0] = 2.5;
+
+  orig.mutable_rows()[1] = 1;
+  orig.mutable_cols()[1] = 4;
+  orig.mutable_values()[1] = 5.2;
+  orig.set_num_nonzeros(2);
+
+  // Who's on earth gonna do this?
+  orig = orig;
+
+  EXPECT_EQ(orig.num_rows(), 2);
+  EXPECT_EQ(orig.num_cols(), 5);
+  ASSERT_EQ(orig.num_nonzeros(), 2);
+  EXPECT_EQ(orig.max_num_nonzeros(), 4);
+
+  EXPECT_EQ(orig.rows()[0], 0);
+  EXPECT_EQ(orig.rows()[1], 1);
+
+  EXPECT_EQ(orig.cols()[0], 1);
+  EXPECT_EQ(orig.cols()[1], 4);
+
+  EXPECT_DOUBLE_EQ(orig.values()[0], 2.5);
+  EXPECT_DOUBLE_EQ(orig.values()[1], 5.2);
+}
+
 TEST(TripletSparseMatrix, AppendRows) {
   // Build one matrix.
   TripletSparseMatrix m(2, 5, 4);