rust: Add unit test for transitive rust dependencies

test cases/rust/20 transitive dependencies/liba/lib.rs

@@ -0,0 +1,3 @@
+pub fn foo() -> i32 {
+    123
+}

test cases/rust/20 transitive dependencies/liba/meson.build

@@ -0,0 +1,5 @@
+liba = static_library('liba', 'lib.rs',
+  rust_crate_type : 'rlib',
+)
+
+liba_dep = declare_dependency(link_with : liba)

test cases/rust/20 transitive dependencies/libb/lib.rs

@@ -0,0 +1,3 @@
+pub fn bar() -> i32 {
+    2 * liba::foo()
+}

test cases/rust/20 transitive dependencies/libb/meson.build

@@ -0,0 +1,6 @@
+libb = static_library('libb', 'lib.rs',
+  rust_crate_type : 'rlib',
+  dependencies : [liba_dep],
+)
+
+libb_dep = declare_dependency(link_with : libb)

test cases/rust/20 transitive dependencies/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("{}", libb::bar());
+}

test cases/rust/20 transitive dependencies/meson.build

@@ -0,0 +1,12 @@
+project('transitive dependencies', 'rust',
+  version : '1.0.0',
+  meson_version : '>= 1.0.0',
+  default_options : ['rust_std=2018'],
+)
+
+subdir('liba')
+subdir('libb')
+
+main = executable('main', 'main.rs',
+  dependencies : [libb_dep],
+)