librustdoc: Use correct heading levels.

- Avoid multiple <h1>s on a page.
- The <h#> tags should follow a semantic hierarchy.
- Cap at h6 (no h7)

src/test/rustdoc/external-cross.rs

@@ -6,5 +6,5 @@
 extern crate external_cross;
 
 // @has host/struct.NeedMoreDocs.html
-// @has - '//h1' 'Cross-crate imported docs'
+// @has - '//h2' 'Cross-crate imported docs'
 pub use external_cross::NeedMoreDocs;

src/test/rustdoc/external-doc.rs

@@ -1,6 +1,6 @@
 // @has external_doc/struct.IncludeStrDocs.html
-// @has - '//h1' 'External Docs'
-// @has - '//h2' 'Inline Docs'
+// @has - '//h2' 'External Docs'
+// @has - '//h3' 'Inline Docs'
 #[doc = include_str!("auxiliary/external-doc.md")]
 /// ## Inline Docs
 pub struct IncludeStrDocs;
@@ -8,7 +8,7 @@ pub struct IncludeStrDocs;
 macro_rules! dir { () => { "auxiliary" } }
 
 // @has external_doc/struct.EagerExpansion.html
-// @has - '//h1' 'External Docs'
+// @has - '//h2' 'External Docs'
 #[doc = include_str!(concat!(dir!(), "/external-doc.md"))]
 /// ## Inline Docs
 pub struct EagerExpansion;

src/test/rustdoc/issue-42760.rs

@@ -1,5 +1,5 @@
 // @has issue_42760/struct.NonGen.html
-// @has - '//h1' 'Example'
+// @has - '//h2' 'Example'
 
 /// Item docs.
 ///

src/test/rustdoc/short-docblock.rs

@@ -2,7 +2,7 @@
 
 // @has foo/index.html '//*[@class="item-right docblock-short"]/p' 'fooo'
 // @!has foo/index.html '//*[@class="item-right docblock-short"]/p/h1' 'fooo'
-// @has foo/fn.foo.html '//h1[@id="fooo"]/a[@href="#fooo"]' 'fooo'
+// @has foo/fn.foo.html '//h2[@id="fooo"]/a[@href="#fooo"]' 'fooo'
 
 /// # fooo
 ///
@@ -11,7 +11,7 @@ pub fn foo() {}
 
 // @has foo/index.html '//*[@class="item-right docblock-short"]/p' 'mooood'
 // @!has foo/index.html '//*[@class="item-right docblock-short"]/p/h2' 'mooood'
-// @has foo/foo/index.html '//h2[@id="mooood"]/a[@href="#mooood"]' 'mooood'
+// @has foo/foo/index.html '//h3[@id="mooood"]/a[@href="#mooood"]' 'mooood'
 
 /// ## mooood
 ///

src/test/rustdoc/smart-punct.rs

@@ -21,7 +21,7 @@
 //! ```
 
 // @has "foo/index.html" "//p" "This is the “start” of the ‘document’! How’d you know that “it’s” the start?"
-// @has "foo/index.html" "//h1" "Header with “smart punct’”"
+// @has "foo/index.html" "//h2" "Header with “smart punct’”"
 // @has "foo/index.html" '//a[@href="https://www.rust-lang.org"]' "link with “smart punct’” – yessiree!"
 // @has "foo/index.html" '//code' "this inline code -- it shouldn't have \"smart punct\""
 // @has "foo/index.html" '//pre' "let x = \"don't smart-punct me -- please!\";"