Auto merge of #54349 - GuillaumeGomez:no-example-lint, r=QuietMisdreavus

[rustdoc] Add lint for doc without codeblocks

Fixes #53805.

r? @QuietMisdreavus

src/test/rustdoc-ui/doc-without-codeblock.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![deny(missing_doc_code_examples)]
+
+/// Some docs.
+pub struct Foo;
+
+/// And then, the princess died.
+pub mod foo {
+    /// Or maybe not because she saved herself!
+    pub fn bar() {}
+}

src/test/rustdoc-ui/doc-without-codeblock.stderr

@@ -0,0 +1,26 @@
+error: Missing code example in this documentation
+   |
+note: lint level defined here
+  --> $DIR/doc-without-codeblock.rs:11:9
+   |
+LL | #![deny(missing_doc_code_examples)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: Missing code example in this documentation
+  --> $DIR/doc-without-codeblock.rs:13:1
+   |
+LL | /// Some docs.
+   | ^^^^^^^^^^^^^^
+
+error: Missing code example in this documentation
+  --> $DIR/doc-without-codeblock.rs:16:1
+   |
+LL | /// And then, the princess died.
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: Missing code example in this documentation
+  --> $DIR/doc-without-codeblock.rs:18:5
+   |
+LL |     /// Or maybe not because she saved herself!
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+