Don't call diag_span_note_once for suppressed lints

src/librustc/lint/mod.rs

@@ -666,6 +666,30 @@ pub fn struct_lint_level<'a>(sess: &'a Session,
         (Level::Forbid, None) => sess.struct_err(msg),
     };
 
+    // Check for future incompatibility lints and issue a stronger warning.
+    let lints = sess.lint_store.borrow();
+    let lint_id = LintId::of(lint);
+    let future_incompatible = lints.future_incompatible(lint_id);
+
+    // If this code originates in a foreign macro, aka something that this crate
+    // did not itself author, then it's likely that there's nothing this crate
+    // can do about it. We probably want to skip the lint entirely.
+    if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
+        // Any suggestions made here are likely to be incorrect, so anything we
+        // emit shouldn't be automatically fixed by rustfix.
+        err.allow_suggestions(false);
+
+        // If this is a future incompatible lint it'll become a hard error, so
+        // we have to emit *something*. Also allow lints to whitelist themselves
+        // on a case-by-case basis for emission in a foreign macro.
+        if future_incompatible.is_none() && !lint.report_in_external_macro {
+            err.cancel();
+            // Don't continue further, since we don't want to have
+            // `diag_span_note_once` called for a diagnostic that isn't emitted.
+            return err;
+        }
+    }
+
     let name = lint.name_lower();
     match src {
         LintSource::Default => {
@@ -715,10 +739,6 @@ pub fn struct_lint_level<'a>(sess: &'a Session,
 
     err.code(DiagnosticId::Lint(name));
 
-    // Check for future incompatibility lints and issue a stronger warning.
-    let lints = sess.lint_store.borrow();
-    let lint_id = LintId::of(lint);
-    let future_incompatible = lints.future_incompatible(lint_id);
     if let Some(future_incompatible) = future_incompatible {
         const STANDARD_MESSAGE: &str =
             "this was previously accepted by the compiler but is being phased out; \
@@ -743,22 +763,6 @@ pub fn struct_lint_level<'a>(sess: &'a Session,
         err.note(&citation);
     }
 
-    // If this code originates in a foreign macro, aka something that this crate
-    // did not itself author, then it's likely that there's nothing this crate
-    // can do about it. We probably want to skip the lint entirely.
-    if err.span.primary_spans().iter().any(|s| in_external_macro(sess, *s)) {
-        // Any suggestions made here are likely to be incorrect, so anything we
-        // emit shouldn't be automatically fixed by rustfix.
-        err.allow_suggestions(false);
-
-        // If this is a future incompatible lint it'll become a hard error, so
-        // we have to emit *something*. Also allow lints to whitelist themselves
-        // on a case-by-case basis for emission in a foreign macro.
-        if future_incompatible.is_none() && !lint.report_in_external_macro {
-            err.cancel()
-        }
-    }
-
     return err
 }