Do not suggest try_into for base types inside of macro expansions

src/librustc_typeck/check/demand.rs

@@ -554,6 +554,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // FIXME(estebank): modify once we decide to suggest `as` casts
             return false;
         }
+        if !self.tcx.sess.source_map().span_to_filename(expr.span).is_real() {
+            // Ignore if span is from within a macro.
+            return false;
+        }
 
         // If casting this expression to a given numeric type would be appropriate in case of a type
         // mismatch.

src/test/ui/suggestions/dont-suggest-try_into-in-macros.rs

@@ -0,0 +1,3 @@
+fn main() {
+    assert_eq!(10u64, 10usize); //~ ERROR mismatched types
+}

src/test/ui/suggestions/dont-suggest-try_into-in-macros.stderr

@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> $DIR/dont-suggest-try_into-in-macros.rs:2:5
+   |
+LL |     assert_eq!(10u64, 10usize);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected u64, found usize
+   |
+   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.