Don't silently ignore errors that happen during rendering

This caught a real, existing bug.

Author: jyn514

src/librustdoc/lib.rs

@@ -689,7 +689,7 @@ fn run_renderer<'tcx, T: formats::FormatRenderer<'tcx>>(
     tcx: TyCtxt<'tcx>,
 ) -> MainResult {
     match formats::run_format::<T>(krate, renderopts, cache, tcx) {
-        Ok(_) => Ok(()),
+        Ok(_) => tcx.sess.has_errors().map_or(Ok(()), Err),
         Err(e) => {
             let mut msg =
                 tcx.sess.struct_err(&format!("couldn't generate documentation: {}", e.error));

src/test/rustdoc/const-evalutation-ice.rs renamed to src/test/rustdoc-ui/const-evalutation-ice.rs

@@ -8,3 +8,4 @@ pub struct S {
 }
 
 pub const N: usize = 0 - (mem::size_of::<S>() != 4) as usize;
+//~^ ERROR evaluation of constant value failed

src/test/rustdoc-ui/const-evalutation-ice.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const-evalutation-ice.rs:10:22
+   |
+LL | pub const N: usize = 0 - (mem::size_of::<S>() != 4) as usize;
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to compute `0_usize - 1_usize`, which would overflow
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.