Add support for upstream's 'edition' flag

Author: phansch

src/header.rs

@@ -297,6 +297,10 @@ impl TestProps {
                     .map(|s| s.to_owned()));
             }
 
+            if let Some(edition) = config.parse_edition(ln) {
+                self.compile_flags.push(format!("--edition={}", edition));
+            }
+
             if let Some(r) = config.parse_revisions(ln) {
                 self.revisions.extend(r);
             }
@@ -609,6 +613,10 @@ impl Config {
     fn parse_rustfix_only_machine_applicable(&self, line: &str) -> bool {
         self.parse_name_directive(line, "rustfix-only-machine-applicable")
     }
+
+    fn parse_edition(&self, line: &str) -> Option<String> {
+        self.parse_name_value_directive(line, "edition")
+    }
 }
 
 pub fn lldb_version_to_int(version_string: &str) -> isize {

test-project/tests/ui/2018-edition.rs

@@ -0,0 +1,8 @@
+// edition:2018
+// compile-pass
+
+pub struct Foo;
+impl Foo {
+    pub async fn foo(&mut self) {
+    }
+}