hide private fmt dependency (#94)

Co-authored-by: Davide Faconti <dfaconti@aurynrobotics.com>

Author: facontidavide

CMakeLists.txt

@@ -67,8 +67,21 @@ if(PJ_BUILD_TESTS)
   find_package(GTest REQUIRED)
 endif()
 
+find_package(fmt REQUIRED)
+
+if(TARGET fmt::fmt-header-only)
+  set(PJ_FMT_TARGET fmt::fmt-header-only)
+elseif(TARGET fmt::fmt)
+  set(PJ_FMT_TARGET fmt::fmt)
+else()
+  message(FATAL_ERROR "fmt is required, but no fmt::fmt or fmt::fmt-header-only target was found.")
+endif()
+
+add_library(pj_internal_fmt INTERFACE)
+target_compile_definitions(pj_internal_fmt INTERFACE FMT_HEADER_ONLY=1)
+target_link_libraries(pj_internal_fmt INTERFACE ${PJ_FMT_TARGET})
+
 if(PJ_BUILD_DATASTORE)
-  find_package(fmt REQUIRED)
   find_package(tsl-robin-map REQUIRED)
   if(PJ_BUILD_TESTS)
     find_package(benchmark CONFIG REQUIRED)

cmake/plotjuggler_coreConfig.cmake.in

@@ -17,7 +17,6 @@ foreach(_comp ${plotjuggler_core_FIND_COMPONENTS})
     set(plotjuggler_core_base_FOUND TRUE)
 
   elseif(_comp STREQUAL "datastore")
-    find_dependency(fmt)
     find_dependency(tsl-robin-map)
     find_dependency(nanoarrow)
     set(plotjuggler_core_datastore_FOUND TRUE)

conanfile.py

@@ -57,6 +57,9 @@ class PlotjugglerCoreConan(ConanFile):
         "arrow/*:with_snappy": True,
         # pj_datastore's Arrow IPC import path needs nanoarrow_ipc + flatcc.
         "nanoarrow/*:with_ipc": True,
+        # fmt is an implementation detail. Compile it header-only so the
+        # static archives do not export a downstream fmt link dependency.
+        "fmt/*:header_only": True,
         # Boost is pulled in transitively by arrow. without_cobalt avoids a
         # known upstream packaging error in recent boost recipes; without_test
         # trims unneeded modules.
@@ -84,9 +87,19 @@ def requirements(self):
         # nlohmann_json appears in public headers (widget_data, plugin_catalog).
         self.requires("nlohmann_json/3.12.0", transitive_headers=True)
 
+        # fmt is private and header-only at build time; do not propagate it
+        # into consumers of this static-library package.
+        self.requires(
+            "fmt/12.1.0",
+            headers=True,
+            libs=False,
+            visible=False,
+            transitive_headers=False,
+            transitive_libs=False,
+        )
+
         if self.options.with_datastore:
-            # fmt + tsl-robin-map are private; nanoarrow is in public headers.
-            self.requires("fmt/12.1.0")
+            # tsl-robin-map is header-only; nanoarrow is in public headers.
             self.requires("tsl-robin-map/1.4.0", transitive_headers=True)
             self.requires("nanoarrow/0.7.0", transitive_headers=True)
 
@@ -161,7 +174,6 @@ def package_info(self):
             ds.includedirs = ["include"]
             ds.requires = [
                 "base",
-                "fmt::fmt",
                 "tsl-robin-map::tsl-robin-map",
                 "nanoarrow::nanoarrow",
             ]

pj_datastore/CMakeLists.txt

@@ -42,7 +42,7 @@ target_link_libraries(pj_datastore
     pj_base
   PRIVATE
     tsl::robin_map
-    fmt::fmt
+    $<BUILD_INTERFACE:pj_internal_fmt>
     ${PJ_NANOARROW_TARGET}
     ${PJ_NANOARROW_IPC_TARGET}
 )

pj_plugins/CMakeLists.txt

@@ -1,4 +1,3 @@
-find_package(fmt REQUIRED)
 find_package(nlohmann_json REQUIRED)
 
 add_library(pj_plugin_loader_detail STATIC
@@ -57,7 +56,7 @@ target_link_libraries(pj_plugin_catalog
   PRIVATE
     pj_plugin_loader_detail
     pj_dialog_protocol
-    fmt::fmt
+    $<BUILD_INTERFACE:pj_internal_fmt>
     ${CMAKE_DL_LIBS}
     nlohmann_json::nlohmann_json
 )