[PATCH v3 3/3] build: RFC - add support for optional dependencies

[Bruce Richardson <bruce.richardson@intel.com>]

In order to remove more libraries from the mandatory list, we need to
have support for optionally having a dependency from a driver or library
to another driver or lib. This patch adds this support by adding a new
optional_deps variable, the contents of which are added to the deps list
if those optional dependencies are present in the build.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 drivers/meson.build | 7 +++++++
 lib/meson.build     | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/drivers/meson.build b/drivers/meson.build
index 5ba534049a..af2d8da5a8 100644
--- a/drivers/meson.build
+++ b/drivers/meson.build
@@ -127,6 +127,7 @@ foreach subpath:subdirs
         includes = [include_directories(drv_path)]
         # set up internal deps. Drivers can append/override as necessary
         deps = std_deps
+        optional_deps = []
         # ext_deps: Stores external library dependency got
         # using dependency() (preferred) or find_library().
         # For the find_library() case (but not with dependency()) we also
@@ -168,6 +169,12 @@ foreach subpath:subdirs
             # get dependency objs from strings
             shared_deps = ext_deps
             static_deps = ext_deps
+            foreach d:optional_deps
+                #if optional dep exists, add it to the deps list
+                if is_variable('shared_rte_' + d)
+                    deps += d
+                endif
+            endforeach
             foreach d:deps
                 if not build
                     break
diff --git a/lib/meson.build b/lib/meson.build
index 72e9138d14..733412c276 100644
--- a/lib/meson.build
+++ b/lib/meson.build
@@ -140,6 +140,7 @@ foreach l:libraries
     # external package/library requirements
     ext_deps = []
     deps = []
+    optional_deps = []
     # eal is standard dependency once built
     if dpdk_conf.has('RTE_LIB_EAL')
         deps += ['eal']
@@ -177,6 +178,12 @@ foreach l:libraries
 
     shared_deps = ext_deps
     static_deps = ext_deps
+    foreach d:optional_deps
+        #if optional dep exists, add it to the deps list
+        if is_variable('shared_rte_' + d)
+            deps += d
+        endif
+    endforeach
     foreach d:deps
         if not build
             break
-- 
2.40.1