build: fix static aws-cpp-sdk

Change-Id: I310830951106f194f6960a6b2d52b5081a7f6156

meson.build

@@ -203,7 +203,7 @@ openssl = dependency('libcrypto', 'openssl', required : true)
 deps += openssl
 
 aws_sdk = dependency('aws-cpp-sdk-core', required : false)
-aws_sdk_transfer = dependency('aws-cpp-sdk-transfer', required : aws_sdk.found())
+aws_sdk_transfer = dependency('aws-cpp-sdk-transfer', required : aws_sdk.found(), fallback : ['aws_sdk', 'aws_cpp_sdk_transfer_dep'])
 if aws_sdk.found()
   # The AWS pkg-config adds -std=c++11.
   # https://github.com/aws/aws-sdk-cpp/issues/2673
@@ -230,7 +230,7 @@ if aws_sdk.found()
   )
 endif
 
-aws_s3 = dependency('aws-cpp-sdk-s3', required : false)
+aws_s3 = dependency('aws-cpp-sdk-s3', required : aws_sdk.found(), fallback : ['aws_sdk', 'aws_cpp_sdk_s3_dep'])
 if aws_s3.found()
   # The AWS pkg-config adds -std=c++11.
   # https://github.com/aws/aws-sdk-cpp/issues/2673

package.nix

@@ -144,6 +144,7 @@ let
     ./meson.options
     ./meson
     ./scripts/meson.build
+    ./subprojects
   ]);
 
   functionalTestFiles = fileset.unions [
@@ -259,7 +260,7 @@ stdenv.mkDerivation (finalAttrs: {
     ++ lib.optional internalApiDocs rapidcheck
     ++ lib.optional hostPlatform.isx86_64 libcpuid
     # There have been issues building these dependencies
-    ++ lib.optional (hostPlatform == buildPlatform) aws-sdk-cpp-nix
+    ++ lib.optional (hostPlatform.canExecute buildPlatform) aws-sdk-cpp-nix
     ++ lib.optionals (finalAttrs.dontBuild) maybePropagatedInputs;
 
   checkInputs = [

subprojects/aws_sdk/meson.build

@@ -0,0 +1,15 @@
+project('aws-sdk', 'cpp')
+
+# dependency() uses Meson's internal logic and generally relies on pkg-config or CMake,
+# but Meson can also use the project's compiler to find a library in the compiler's search
+# path. Not in the dependency() function, though. You have to use compiler.find_library(),
+# and Meson doesn't have a way to tell dependency() to simply fallback to find_library().
+# It *does* however allow dependency() to fallback to a variable defined in a subproject,
+# Hence: this file.
+
+# For some reason, these specific components of the AWS C++ SDK aren't found by CMake when
+# compiling statically, and `pkgsStatic.aws-sdk-cpp` doesn't even have a pkg-config at all.
+
+cxx = meson.get_compiler('cpp')
+aws_cpp_sdk_transfer_dep = cxx.find_library('aws-cpp-sdk-transfer')
+aws_cpp_sdk_s3_dep = cxx.find_library('aws-cpp-sdk-s3')