ninja: fix handling of rust structured_sources in rare case

In the even that all of the inputs are generated, and they're all
generated into the same folder, and there are no subfolders, we would
fail to correctly handle all of the files after the main file. Let's fix
that.t

mesonbuild/backend/ninjabackend.py

@@ -1709,17 +1709,24 @@ class NinjaBackend(backends.Backend):
                 _ods, main_rust_file = self.__generate_compile_structure(target)
                 orderdeps.extend(_ods)
             else:
+                # The only way to get here is to have only files in the "root"
+                # positional argument, which are all generated into the same
+                # directory
                 g = target.structured_sources.first_file()
 
                 if isinstance(g, File):
                     main_rust_file = g.rel_to_builddir(self.build_to_src)
                 elif isinstance(g, GeneratedList):
-                    main_rust_file = os.path.join(self.get_target_private_dir(target), i)
+                    main_rust_file = os.path.join(self.get_target_private_dir(target), g.get_outputs()[0])
                 else:
-                    main_rust_file = os.path.join(g.get_subdir(), i)
-                orderdeps.extend([os.path.join(self.build_to_src, target.subdir, s)
-                                  for s in  target.structured_sources.as_list()])
+                    main_rust_file = os.path.join(g.get_subdir(), g.get_outputs()[0])
 
+                for f in target.structured_sources.as_list():
+                    if isinstance(f, File):
+                        orderdeps.append(f.rel_to_builddir(self.build_to_src))
+                    else:
+                        orderdeps.extend([os.path.join(self.build_to_src, f.subdir, s)
+                                          for s in f.get_outputs()])
 
         for i in target.get_sources():
             if not rustc.can_compile(i):

test cases/rust/18 structured sources/main-gen-copy.rs

@@ -0,0 +1,5 @@
+include!(r#"@dir@/include.rs"#);
+
+pub fn main() {
+    priv_func();
+}

test cases/rust/18 structured sources/meson.build

@@ -37,3 +37,22 @@ executable(
 )
 
 test('no-copy', find_program('no_copy_test.py'), args : meson.current_build_dir())
+
+subdir('src2')
+
+executable('copy-no-gen', srcs2)
+
+m_src = configure_file(
+  input : 'main-gen-copy.rs',
+  output : 'main-gen-copy.rs',
+  configuration : {'dir' : meson.current_build_dir().replace('\\', '/')},
+)
+
+m_src2 = configure_file(
+  input : 'priv.rs',
+  output : 'include.rs',
+  copy : true
+)
+
+executable('gen-no-copy', structured_sources([m_src, m_src2]))
+

test cases/rust/18 structured sources/priv.rs

@@ -0,0 +1,3 @@
+fn priv_func() {
+    std::process::exit(0);
+}

test cases/rust/18 structured sources/src2/meson.build

@@ -0,0 +1,4 @@
+srcs2 = structured_sources(
+  ['main-unique.rs'],
+  {'foo': 'foo/mod.rs'},
+)