Rollup merge of rust-lang#45764 - QuietMisdreavus:rustdoc-doctest-lints, r=GuillaumeGomez

rustdoc: add #[allow(unused)] to every doctest

More information in rust-lang#45750 - this is behavior that was documented but not actually implemented.

I also reordered how outer attributes are applied to doctests. Previously, attributes from `#![doc(test(attr(...)))]` would be applied *after* attributes from within the test itself, meaning if a doctest tried to override lints that would be set crate-wide, it wouldn't work at all. This gives a better scope of how lints can be applied.

Closes rust-lang#45750

Author: kennytm

src/librustdoc/test.rs

@@ -337,15 +337,23 @@ pub fn make_test(s: &str,
 
     let mut prog = String::new();
 
-    // First push any outer attributes from the example, assuming they
-    // are intended to be crate attributes.
-    prog.push_str(&crate_attrs);
+    if opts.attrs.is_empty() {
+        // If there aren't any attributes supplied by #![doc(test(attr(...)))], then allow some
+        // lints that are commonly triggered in doctests. The crate-level test attributes are
+        // commonly used to make tests fail in case they trigger warnings, so having this there in
+        // that case may cause some tests to pass when they shouldn't have.
+        prog.push_str("#![allow(unused)]\n");
+    }
 
-    // Next, any attributes for other aspects such as lints.
+    // Next, any attributes that came from the crate root via #![doc(test(attr(...)))].
     for attr in &opts.attrs {
         prog.push_str(&format!("#![{}]\n", attr));
     }
 
+    // Now push any outer attributes from the example, assuming they
+    // are intended to be crate attributes.
+    prog.push_str(&crate_attrs);
+
     // Don't inject `extern crate std` because it's already injected by the
     // compiler.
     if !s.contains("extern crate") && !opts.no_crate_inject && cratename != Some("std") {

src/test/rustdoc/playground-arg.rs

@@ -21,4 +21,4 @@
 pub fn dummy() {}
 
 // ensure that `extern crate foo;` was inserted into code snips automatically:
-// @matches foo/index.html '//a[@class="test-arrow"][@href="https://example.com/?code=extern%20crate%20foo%3B%0Afn%20main()%20%7B%0Ause%20foo%3A%3Adummy%3B%0Adummy()%3B%0A%7D"]' "Run"
+// @matches foo/index.html '//a[@class="test-arrow"][@href="https://example.com/?code=%23!%5Ballow(unused)%5D%0Aextern%20crate%20foo%3B%0Afn%20main()%20%7B%0Ause%20foo%3A%3Adummy%3B%0Adummy()%3B%0A%7D"]' "Run"

src/test/rustdoc/playground.rs

@@ -34,6 +34,6 @@
 //! }
 //! ```
 
-// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=fn%20main()%20%7B%0A%20%20%20%20println!(%22Hello%2C%20world!%22)%3B%0A%7D%0A"]' "Run"
-// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=fn%20main()%20%7B%0Aprintln!(%22Hello%2C%20world!%22)%3B%0A%7D"]' "Run"
-// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=%23!%5Bfeature(something)%5D%0A%0Afn%20main()%20%7B%0A%20%20%20%20println!(%22Hello%2C%20world!%22)%3B%0A%7D%0A&version=nightly"]' "Run"
+// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0A%20%20%20%20println!(%22Hello%2C%20world!%22)%3B%0A%7D%0A"]' "Run"
+// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Aprintln!(%22Hello%2C%20world!%22)%3B%0A%7D"]' "Run"
+// @matches foo/index.html '//a[@class="test-arrow"][@href="https://www.example.com/?code=%23!%5Ballow(unused)%5D%0A%23!%5Bfeature(something)%5D%0A%0Afn%20main()%20%7B%0A%20%20%20%20println!(%22Hello%2C%20world!%22)%3B%0A%7D%0A&version=nightly"]' "Run"