rust: implement support for --edition

Using the std option, so now `rust_std=..` will work. I've chosen to use
"std" even though rust calls these "editions", as meson refers to
language versions as "standards", which makes meson feel more uniform,
and be less surprising.

Fixes: #5100

3 files changed, 30 insertions, 0 deletions

diff --git a/test cases/rust/10 language stds/2015.rs b/test cases/rust/10 language stds/2015.rs
new file mode 100644
index 0000000..4d28c57
--- /dev/null
+++ b/test cases/rust/10 language stds/2015.rs
@@ -0,0 +1,3 @@
+trait Foo {
+    fn foo(&self, Box<dyn Foo>);
+}
diff --git a/test cases/rust/10 language stds/2018.rs b/test cases/rust/10 language stds/2018.rs
new file mode 100644
index 0000000..4009154
--- /dev/null
+++ b/test cases/rust/10 language stds/2018.rs
@@ -0,0 +1,9 @@
+const fn foo(x: i32) -> i32 {
+    return x + 1;
+}
+
+const VALUE: i32 = foo(-1);
+
+pub fn main() {
+    std::process::exit(VALUE);
+}
diff --git a/test cases/rust/10 language stds/meson.build b/test cases/rust/10 language stds/meson.build
new file mode 100644
index 0000000..9944339
--- /dev/null
+++ b/test cases/rust/10 language stds/meson.build
@@ -0,0 +1,18 @@
+project('rust std options', 'rust')
+
+# this only works in 2018
+new = executable(
+  'new',
+  '2018.rs',
+  override_options : ['rust_std=2018'],
+)
+
+# this only works in 2015
+old = static_library(
+  'old',
+  '2015.rs',
+  override_options : ['rust_std=2015'],
+)
+
+
+test('2018 std', new)