build: fetch libbsdl from git when ../libbsdl is absent

Fall back to FetchContent (BSDL_GIT_REPOSITORY/BSDL_GIT_TAG) so a fresh
clone configures without a manual side-checkout.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CMakeLists.txt

@@ -16,12 +16,25 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 include(EssimFrontend)
 
 # ----------------------------------------------------------------- core deps
-# libbsdl — standalone BSDL parser (LGPL-2.1), dynamically linked (EUPL-1.2,
-# which the LGPL permits). Override its path with -DBSDL_DIR=...
+# libbsdl — standalone BSDL parser (LGPL-2.1), dynamically linked. Local sibling
+# ../libbsdl (override -DBSDL_DIR=...) if present, else fetched from git.
 set(BSDL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../libbsdl" CACHE PATH "libbsdl source tree")
+set(BSDL_GIT_REPOSITORY "https://git.beafrancois.fr/electronics/libbsdl.git" CACHE STRING "libbsdl git repo (used when BSDL_DIR is absent)")
+set(BSDL_GIT_TAG "main" CACHE STRING "libbsdl git revision to fetch")
 set(BSDL_BUILD_CLI   OFF CACHE BOOL "" FORCE)
 set(BSDL_BUILD_TESTS OFF CACHE BOOL "" FORCE)
-add_subdirectory(${BSDL_DIR} ${CMAKE_BINARY_DIR}/libbsdl)
+if(EXISTS "${BSDL_DIR}/CMakeLists.txt")
+  message(STATUS "essim: libbsdl from local tree '${BSDL_DIR}'")
+  add_subdirectory(${BSDL_DIR} ${CMAKE_BINARY_DIR}/libbsdl)
+else()
+  message(STATUS "essim: libbsdl absent — fetching ${BSDL_GIT_REPOSITORY} (${BSDL_GIT_TAG})")
+  FetchContent_Declare(libbsdl
+    GIT_REPOSITORY ${BSDL_GIT_REPOSITORY}
+    GIT_TAG        ${BSDL_GIT_TAG}
+    GIT_SHALLOW    TRUE
+  )
+  FetchContent_MakeAvailable(libbsdl)
+endif()
 
 find_package(libzip REQUIRED)
 find_package(pugixml REQUIRED)

DESIGN.md

@@ -19,9 +19,10 @@ cmake --build build -j
 - **Core system dependencies** (via `find_package`): `libzip` (`libzip::zip`)
   and `pugixml` (`pugixml::pugixml`) for the ODS importer. Arch:
   `pacman -S libzip pugixml`; Debian/Ubuntu: `libzip-dev libpugixml-dev`.
-- **`libbsdl`** (standalone BSDL parser, LGPL-2.1) — sibling repo at
-  `../libbsdl`, `add_subdirectory` (override `-DBSDL_DIR=...`), linked
-  dynamically **into the core** (`bsdl::bsdl`).
+- **`libbsdl`** (standalone BSDL parser, LGPL-2.1) — linked dynamically **into
+  the core** (`bsdl::bsdl`). Local sibling `../libbsdl` via `add_subdirectory`
+  (override `-DBSDL_DIR=...`) when `${BSDL_DIR}/CMakeLists.txt` exists, otherwise
+  `FetchContent` from `-DBSDL_GIT_REPOSITORY` (`-DBSDL_GIT_TAG`, default `main`).
 - **FTXUI** is fetched by the **tui frontend only**
   (`src/frontends/tui/CMakeLists.txt`), never by the core.
 - Sources are globbed per layer: `src/core/*.cpp` → `essim_core`,

README.md

@@ -44,10 +44,11 @@ Step-by-step walkthroughs for both the batch and TUI workflows are in
   - Debian/Ubuntu — `sudo apt install libzip-dev libpugixml-dev`
   - Arch — `sudo pacman -S libzip pugixml`
   - Fedora — `sudo dnf install libzip-devel pugixml-devel`
-- **libbsdl** — the standalone BSDL parser, a sibling repo expected at
-  `../libbsdl`, pulled in via `add_subdirectory` and linked dynamically.
-  Override its location with `-DBSDL_DIR=/path/to/libbsdl`. Powers the
-  `attach-bsdl` command and the pin/JTAG checks.
+- **libbsdl** — the standalone BSDL parser, linked dynamically. Uses a sibling
+  checkout at `../libbsdl` (override `-DBSDL_DIR=/path/to/libbsdl`) if present,
+  else fetched from git automatically (`-DBSDL_GIT_REPOSITORY=...`,
+  `-DBSDL_GIT_TAG=...`, default branch `main`). Powers the `attach-bsdl` command
+  and the pin/JTAG checks.
 - Fetched automatically via `FetchContent` (nothing to install): **FTXUI**
   v6.1.9 — only when building the **tui** frontend — and **doctest** v2.4.11
   for the tests.