[WIP] Use TaskChampion 0.7.0, now via cxx instead of hand-rolled FFI

TC 0.7.0 introduces a new `TaskData` type that maps to Taskwarrior's
`Task` type more cleanly. It also introduces the idea of gathering lists
of operations and "committing" them to a replica.

A consequence of this change is that TaskChampion no longer
automatically maintains dependency information, so Taskwarrior must do
so, with its `TDB2::dependency_sync` method. This method does a very
similar thing to what TaskChampion had been doing, so this is a shift of
responsibility but not a major performance difference.

Cxx is .. not great. It is missing a lot of useful things that make a
general-purpose bridge impractical:

 - no support for trait objects
 - no support for `Option<T>` (dtolnay/cxx#87)
 - no support for `Vec<Box<..>>`

As a result, some creativity is required in writing the bridge, for
example returning a `Vec<OptionTaskData>` from `all_task_data` to allow
individual `TaskData` values to be "taken" from the vector.

That said, Cxx is the current state-of-the-art, and does a good job of
ensuring memory safety, at the cost of some slightly awkward APIs.

Subsequent work can remove the "TDB2" layer and allow commands and other
parts of Taskwarrior to interface directly with the `Replica`.

TODO:
 - reference released `taskchampion 0.7.0`

.github/workflows/checks.yml

@@ -61,39 +61,3 @@ jobs:
         with:
           command: fmt
           args: --all -- --check
-
-  codegen:
-    runs-on: ubuntu-latest
-    name: "codegen"
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Cache cargo registry
-        uses: actions/cache@v4
-        with:
-          path: ~/.cargo/registry
-          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
-
-      - name: Cache cargo build
-        uses: actions/cache@v4
-        with:
-          path: target
-          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
-
-      - uses: actions-rs/toolchain@v1
-        with:
-          toolchain: "1.70.0" # MSRV
-          override: true
-
-      - uses: actions-rs/[email protected]
-        with:
-          command: xtask
-          args: codegen
-
-      - name: check for changes
-        run: |
-          if ! git diff; then
-            echo "Generated code not up-to-date;
-            run `cargo run --package xtask -- codegen` and commit the result";
-            exit 1;
-          fi

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "src/libshared"]
 	path = src/libshared
 	url = https://github.com/GothenburgBitFactory/libshared.git
-[submodule "src/tc/corrosion"]
-	path = src/tc/corrosion
+[submodule "src/taskchampion-cpp/corrosion"]
+	path = src/taskchampion-cpp/corrosion
 	url = https://github.com/corrosion-rs/corrosion.git

CMakeLists.txt

@@ -26,13 +26,13 @@ if (ENABLE_WASM)
 endif (ENABLE_WASM)
 
 message ("-- Looking for git submodules")
-if (EXISTS ${CMAKE_SOURCE_DIR}/src/libshared/src AND EXISTS ${CMAKE_SOURCE_DIR}/src/tc/corrosion)
+if (EXISTS ${CMAKE_SOURCE_DIR}/src/libshared/src AND EXISTS ${CMAKE_SOURCE_DIR}/src/taskchampion-cpp/corrosion)
   message ("-- Found git submodules")
 else (EXISTS ${CMAKE_SOURCE_DIR}/src/libshared/src)
   message ("-- Cloning git submodules")
   execute_process (COMMAND git submodule update --init
                    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
-endif (EXISTS ${CMAKE_SOURCE_DIR}/src/libshared/src AND EXISTS ${CMAKE_SOURCE_DIR}/src/tc/corrosion)
+endif (EXISTS ${CMAKE_SOURCE_DIR}/src/libshared/src AND EXISTS ${CMAKE_SOURCE_DIR}/src/taskchampion-cpp/corrosion)
 
 message ("-- Looking for SHA1 references")
 if (EXISTS ${CMAKE_SOURCE_DIR}/.git/index)
@@ -142,7 +142,7 @@ configure_file (
 
 add_subdirectory (src)
 add_subdirectory (src/commands)
-add_subdirectory (src/tc)
+add_subdirectory (src/taskchampion-cpp)
 add_subdirectory (src/columns)
 add_subdirectory (doc)
 add_subdirectory (scripts)