rustc: Disallow machine applicability in foreign macros

Recent changes to lints disallowed lints from being emitted against code located
in foreign macros, except for future-incompatible lints. For a future
incompatible lint, however, the automatic suggestions may not be applicable!

This commit updates this code path to force all applicability suggestions made
to foreign macros to never be `MachineApplicable`. This should avoid rustfix
actually attempting fixing these suggestions, causing non-compiling code to be
produced.

Closes rust-lang/cargo#5799

src/tools/compiletest/src/header.rs

@@ -231,6 +231,7 @@ pub struct TestProps {
     pub normalize_stderr: Vec<(String, String)>,
     pub failure_status: i32,
     pub run_rustfix: bool,
+    pub rustfix_only_machine_applicable: bool,
 }
 
 impl TestProps {
@@ -263,6 +264,7 @@ impl TestProps {
             normalize_stderr: vec![],
             failure_status: -1,
             run_rustfix: false,
+            rustfix_only_machine_applicable: false,
         }
     }
 
@@ -397,6 +399,11 @@ impl TestProps {
             if !self.run_rustfix {
                 self.run_rustfix = config.parse_run_rustfix(ln);
             }
+
+            if !self.rustfix_only_machine_applicable {
+                self.rustfix_only_machine_applicable =
+                    config.parse_rustfix_only_machine_applicable(ln);
+            }
         });
 
         if self.failure_status == -1 {
@@ -663,6 +670,10 @@ impl Config {
         self.parse_name_directive(line, "run-rustfix")
     }
 
+    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")
     }

src/tools/compiletest/src/runtest.rs

@@ -2624,7 +2624,11 @@ impl<'test> TestCx<'test> {
             let suggestions = get_suggestions_from_json(
                 &proc_res.stderr,
                 &HashSet::new(),
-                Filter::Everything,
+                if self.props.rustfix_only_machine_applicable {
+                    Filter::MachineApplicableOnly
+                } else {
+                    Filter::Everything
+                },
             ).unwrap();
             let fixed_code = apply_suggestions(&unfixed_code, &suggestions).expect(&format!(
                 "failed to apply suggestions for {:?} with rustfix",
@@ -2686,7 +2690,7 @@ impl<'test> TestCx<'test> {
             if !res.status.success() {
                 self.fatal_proc_rec("failed to compile fixed code", &res);
             }
-            if !res.stderr.is_empty() {
+            if !res.stderr.is_empty() && !self.props.rustfix_only_machine_applicable {
                 self.fatal_proc_rec("fixed code is still producing diagnostics", &res);
             }
         }