rust: rlib/staticlib should not link with C libraries

mesonbuild/backend/ninjabackend.py

@@ -1997,6 +1997,13 @@ def generate_rust_target(self, target: build.BuildTarget) -> None:
 
             # Link a C ABI library
 
+            # rlib/staticlib does not need to link with C libraries, it would
+            # cause rustc to include .o objects contained in C static libraries
+            # inside the archive. That would in turn cause multiple definition
+            # of symbols in the case of a diamond dependency graph.
+            if isinstance(target, build.StaticLibrary):
+                continue
+
             if isinstance(d, build.StaticLibrary):
                 external_deps.extend(d.external_deps)
 

test cases/rust/20 transitive dependencies/diamond/func.c

@@ -0,0 +1,4 @@
+int c_func(void);
+int c_func(void) {
+    return 123;
+}

test cases/rust/20 transitive dependencies/diamond/main.c

@@ -0,0 +1,5 @@
+int r3(void);
+
+int main_func(void) {
+    return r3() == 246 ? 0 : 1;
+}

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

@@ -0,0 +1,17 @@
+# Regression test for a diamond dependency graph:
+#          ┌►R1┐
+# main-►R3─┤   ├─►C1
+#          └►R2┘
+# Both libr1.rlib and libr2.rlib used to contain func.c.o. That was causing
+# libr3.rlib to have duplicated func.c.o and then libmain.so failed to link:
+# multiple definition of `c_func'.
+
+libc1 = static_library('c1', 'func.c')
+libr1 = static_library('r1', 'r1.rs', link_with: libc1)
+libr2 = static_library('r2', 'r2.rs', link_with: libc1)
+libr3 = static_library('r3', 'r3.rs',
+  link_with: [libr1, libr2],
+  rust_abi: 'c',
+)
+
+shared_library('main', 'main.c', link_whole: [libr3])

test cases/rust/20 transitive dependencies/diamond/r1.rs

@@ -0,0 +1,9 @@
+extern "C" {
+    fn c_func() -> i32;
+}
+
+pub fn r1() -> i32 {
+    unsafe {
+        c_func()
+    }
+}

test cases/rust/20 transitive dependencies/diamond/r2.rs

@@ -0,0 +1,9 @@
+extern "C" {
+    fn c_func() -> i32;
+}
+
+pub fn r2() -> i32 {
+    unsafe {
+        c_func()
+    }
+}

test cases/rust/20 transitive dependencies/diamond/r3.rs

@@ -0,0 +1,4 @@
+#[no_mangle]
+pub fn r3() -> i32 {
+    r1::r1() + r2::r2()
+}

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

@@ -25,3 +25,5 @@ exe = executable('footest', 'foo.c',
   link_with: foo,
 )
 test('footest', exe)
+
+subdir('diamond')