Do not read past the end of the file being patched

src/applier.cpp

@@ -88,6 +88,9 @@ static LineNumber write_define_hunk(LineWriter& output, const Hunk& hunk, const
 
     for (const auto& patch_line : hunk.lines) {
         if (patch_line.operation == ' ') {
+            if (line_number >= lines.size())
+                continue;
+
             const auto& line = lines.at(line_number);
             ++line_number;
             if (define_state != DefineState::Outside) {
@@ -105,6 +108,9 @@ static LineNumber write_define_hunk(LineWriter& output, const Hunk& hunk, const
             }
             output << patch_line.line;
         } else if (patch_line.operation == '-') {
+            if (line_number >= lines.size())
+                continue;
+
             const auto& line = lines.at(line_number);
             ++line_number;
 
@@ -136,12 +142,16 @@ static LineNumber write_hunk(LineWriter& output, const Hunk& hunk, const Locatio
 
     for (const auto& patch_line : hunk.lines) {
         if (patch_line.operation == ' ') {
+            if (line_number >= lines.size())
+                continue;
+
             output << lines.at(line_number);
             ++line_number;
         } else if (patch_line.operation == '+') {
             output << patch_line.line;
         } else if (patch_line.operation == '-') {
-            ++line_number;
+            if (line_number < lines.size())
+                ++line_number;
         }
     }
 

src/locator.cpp

@@ -105,7 +105,8 @@ Location locate_hunk(const std::vector<Line>& content, const Hunk& hunk, bool ig
     if (hunk.old_file_range.number_of_lines == 0) {
         if (hunk.old_file_range.start_line == 0 && !content.empty())
             return {};
-        return { offset_guess, 0, 0 };
+        const auto end = static_cast<LineNumber>(content.size());
+        return { std::min(std::max<LineNumber>(offset_guess, 0), end), 0, 0 };
     }
 
     LineNumber patch_prefix_content = 0;

tests/test_applier.cpp

@@ -90,6 +90,88 @@ int another()
     EXPECT_FILE_EQ("a.rej", patch);
 }
 
+static void write_context_past_end_of_file_patch()
+{
+    Patch::File file("diff.patch", std::ios_base::out);
+    file << R"(--- a
++++ a
+@@ -1,5 +1,5 @@
+ a
+-b
++B
+ c
+ ZZZ
+ QQQ
+)";
+    file.close();
+}
+
+static void write_three_line_file()
+{
+    Patch::File file("a", std::ios_base::out);
+    file << "a\nb\nc\n";
+    file.close();
+}
+
+COMPAT_TEST(applier_insertion_past_end_of_file)
+{
+    {
+        Patch::File file("diff.patch", std::ios_base::out);
+        file << R"(--- a
++++ a
+@@ -100,0 +100,1 @@
++inserted
+)";
+        file.close();
+    }
+
+    write_three_line_file();
+
+    Process process(patch_path, { patch_path, "--force", "-i", "diff.patch", nullptr });
+
+    EXPECT_EQ(process.stdout_data(), "patching file a\n");
+    EXPECT_EQ(process.stderr_data(), "");
+    EXPECT_EQ(process.return_code(), 0);
+    EXPECT_FILE_EQ("a", "a\nb\nc\ninserted\n");
+}
+
+COMPAT_TEST(applier_fuzz_matches_context_past_end_of_file)
+{
+    write_context_past_end_of_file_patch();
+    write_three_line_file();
+
+    Process process(patch_path, { patch_path, "--force", "--fuzz=3", "-i", "diff.patch", nullptr });
+
+    EXPECT_EQ(process.stdout_data(), R"(patching file a
+Hunk #1 succeeded at 1 with fuzz 2.
+)");
+    EXPECT_EQ(process.stderr_data(), "");
+    EXPECT_EQ(process.return_code(), 0);
+    EXPECT_FILE_EQ("a", "a\nB\nc\n");
+}
+
+COMPAT_TEST(applier_fuzz_matches_context_past_end_of_file_with_define)
+{
+    write_context_past_end_of_file_patch();
+    write_three_line_file();
+
+    Process process(patch_path, { patch_path, "--force", "--fuzz=3", "-D", "FOO", "-i", "diff.patch", nullptr });
+
+    EXPECT_EQ(process.stdout_data(), R"(patching file a
+Hunk #1 succeeded at 1 with fuzz 2.
+)");
+    EXPECT_EQ(process.stderr_data(), "");
+    EXPECT_EQ(process.return_code(), 0);
+    EXPECT_FILE_EQ("a", R"(a
+#ifndef FOO
+b
+#else
+B
+#endif
+c
+)");
+}
+
 COMPAT_TEST(applier_end_of_file_hunk_requires_fuzz_when_no_longer_at_end)
 {
     const std::string patch = R"(--- a