patch+LibDiff: Add support for applying patches with preprocessor macro

Tests/Utilities/TestPatch.cpp

@@ -276,3 +276,40 @@ TEST_CASE(patch_with_timestamp_separated_by_tab)
     run_patch(ExpectSuccess::Yes, {}, patch, "patching file 1\n"sv);
     EXPECT_FILE_EQ(ByteString::formatted("{}/1", s_test_dir), "a\n"sv);
 }
+
+TEST_CASE(patch_defines_add_remove)
+{
+    PatchSetup setup;
+
+    StringView patch = R"(
+--- file.cpp
++++ file.cpp
+@@ -1,4 +1,4 @@
+ int main()
+ {
+-    return 0;
++    return 1;
+ }
+)"sv;
+
+    auto file = R"(int main()
+{
+    return 0;
+}
+)"sv;
+
+    auto input = MUST(Core::File::open(ByteString::formatted("{}/file.cpp", s_test_dir), Core::File::OpenMode::Write));
+    MUST(input->write_until_depleted(file.bytes()));
+
+    run_patch(ExpectSuccess::Yes, { "--ifdef", "TEST_PATCH" }, patch);
+
+    EXPECT_FILE_EQ(ByteString::formatted("{}/file.cpp", s_test_dir), R"(int main()
+{
+#ifndef TEST_PATCH
+    return 0;
+#else
+    return 1;
+#endif
+}
+)");
+}

Userland/Libraries/LibDiff/Applier.cpp

@@ -130,7 +130,59 @@ static ErrorOr<size_t> write_hunk(Stream& out, Hunk const& hunk, Location const&
     return line_number;
 }
 
-ErrorOr<void> apply_patch(Stream& out, Vector<StringView> const& lines, Patch const& patch)
+static ErrorOr<size_t> write_define_hunk(Stream& out, Hunk const& hunk, Location const& location, Vector<StringView> const& lines, StringView define)
+{
+    enum class State {
+        Outside,
+        InsideIFNDEF,
+        InsideIFDEF,
+        InsideELSE,
+    };
+
+    auto state = State::Outside;
+
+    auto line_number = location.line_number;
+
+    for (auto const& patch_line : hunk.lines) {
+        if (patch_line.operation == Diff::Line::Operation::Context) {
+            auto const& line = lines.at(line_number);
+            ++line_number;
+            if (state != State::Outside) {
+                TRY(out.write_formatted("#endif\n"));
+                state = State::Outside;
+            }
+            TRY(out.write_formatted("{}\n", line));
+        } else if (patch_line.operation == Diff::Line::Operation::Addition) {
+            if (state == State::Outside) {
+                state = State::InsideIFDEF;
+                TRY(out.write_formatted("#ifdef {}\n", define));
+            } else if (state == State::InsideIFNDEF) {
+                state = State::InsideELSE;
+                TRY(out.write_formatted("#else\n"));
+            }
+            TRY(out.write_formatted("{}\n", patch_line.content));
+        } else if (patch_line.operation == Diff::Line::Operation::Removal) {
+            auto const& line = lines.at(line_number);
+            ++line_number;
+
+            if (state == State::Outside) {
+                state = State::InsideIFNDEF;
+                TRY(out.write_formatted("#ifndef {}\n", define));
+            } else if (state == State::InsideIFDEF) {
+                state = State::InsideELSE;
+                TRY(out.write_formatted("#else\n"));
+            }
+            TRY(out.write_formatted("{}\n", line));
+        }
+    }
+
+    if (state != State::Outside)
+        TRY(out.write_formatted("#endif\n"));
+
+    return line_number;
+}
+
+ErrorOr<void> apply_patch(Stream& out, Vector<StringView> const& lines, Patch const& patch, Optional<StringView> const& define)
 {
     size_t line_number = 0; // NOTE: relative to 'old' file.
     ssize_t offset_error = 0;
@@ -150,7 +202,10 @@ ErrorOr<void> apply_patch(Stream& out, Vector<StringView> const& lines, Patch co
             TRY(out.write_formatted("{}\n", lines.at(line_number)));
 
         // Then output the hunk to what we hope is the correct location in the file.
-        line_number = TRY(write_hunk(out, hunk, location, lines));
+        if (define.has_value())
+            line_number = TRY(write_define_hunk(out, hunk, location, lines, define.value()));
+        else
+            line_number = TRY(write_hunk(out, hunk, location, lines));
     }
 
     // We've finished applying all hunks, write out anything from the old file we haven't already.

Userland/Libraries/LibDiff/Applier.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, Shannon Booth <shannon@serenityos.org>
+ * Copyright (c) 2023-2024, Shannon Booth <shannon@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -11,6 +11,6 @@
 
 namespace Diff {
 
-ErrorOr<void> apply_patch(Stream& out, Vector<StringView> const& lines, Patch const& patch);
+ErrorOr<void> apply_patch(Stream& out, Vector<StringView> const& lines, Patch const& patch, Optional<StringView> const& define = {});
 
 }

Userland/Utilities/patch.cpp

@@ -39,7 +39,7 @@ static ErrorOr<ByteBuffer> read_content(StringView path_of_file_to_patch, Diff::
     return ByteBuffer {};
 }
 
-static ErrorOr<void> do_patch(StringView path_of_file_to_patch, Diff::Patch const& patch)
+static ErrorOr<void> do_patch(StringView path_of_file_to_patch, Diff::Patch const& patch, Optional<StringView> const& define = {})
 {
     ByteBuffer content = TRY(read_content(path_of_file_to_patch, patch));
     auto lines = StringView(content).lines();
@@ -49,7 +49,7 @@ static ErrorOr<void> do_patch(StringView path_of_file_to_patch, Diff::Patch cons
     auto tmp_file = TRY(Core::File::adopt_fd(TRY(Core::System::mkstemp(tmp_output)), Core::File::OpenMode::ReadWrite));
     StringView tmp_path { tmp_output, sizeof(tmp_output) };
 
-    TRY(Diff::apply_patch(*tmp_file, lines, patch));
+    TRY(Diff::apply_patch(*tmp_file, lines, patch, define));
 
     // If the patched file ends up being empty, remove it, as the patch was a removal.
     // Note that we cannot simply rely on the patch successfully applying and the patch claiming it is removing the file
@@ -67,11 +67,13 @@ static ErrorOr<void> do_patch(StringView path_of_file_to_patch, Diff::Patch cons
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     StringView directory;
+    Optional<StringView> define;
     Optional<size_t> strip_count;
 
     Core::ArgsParser args_parser;
     args_parser.add_option(directory, "Change the working directory to <directory> before applying the patch file", "directory", 'd', "directory");
     args_parser.add_option(strip_count, "Strip given number of leading path components from file names (defaults as basename)", "strip", 'p', "count");
+    args_parser.add_option(define, "Apply merged patch content separated by C preprocessor macros", "ifdef", 'D', "define");
     args_parser.parse(arguments);
 
     if (!directory.is_null())
@@ -100,7 +102,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         }
 
         outln("patching file {}", to_patch);
-        TRY(do_patch(to_patch, patch));
+        TRY(do_patch(to_patch, patch, define));
     }
 
     return 0;