Rollup merge of #93217 - willcrichton:example-analyzer, r=GuillaumeGomez

Improve Rustdoc UI for scraped examples with multiline arguments, fix overflow in line numbers

This PR improves a few aspects of the scrape examples feature in Rustdoc.
* Only function names and not the full call expression are highlighted.
* For call-sites with multiline arguments, the minimized code viewer will scroll to the top of the call-site rather than the middle if the argument is larger than the viewer size, ensuring that the function name is visible.
* This fixes an issue where the line numbers column had a visible x-scroll bar.

r? `@GuillaumeGomez`

src/doc/rustdoc/src/SUMMARY.md

@@ -9,6 +9,7 @@
     - [Linking to items by name](write-documentation/linking-to-items-by-name.md)
     - [Documentation tests](write-documentation/documentation-tests.md)
 - [Rustdoc-specific lints](lints.md)
+- [Scraped examples](scraped-examples.md)
 - [Advanced features](advanced-features.md)
 - [Unstable features](unstable-features.md)
 - [Deprecated features](deprecated-features.md)

src/doc/rustdoc/src/scraped-examples.md

@@ -0,0 +1,55 @@
+# Scraped examples
+
+Rustdoc has an unstable feature where it can automatically scrape examples of items being documented from the `examples/` directory of a Cargo workspace. These examples will be included within the generated documentation for that item. For example, if your library contains a public function:
+
+```rust,ignore (needs-other-file)
+// a_crate/src/lib.rs
+pub fn a_func() {}
+```
+
+And you have an example calling this function:
+
+```rust,ignore (needs-other-file)
+// a_crate/examples/ex.rs
+fn main() {
+  a_crate::a_func();
+}
+```
+
+Then this code snippet will be included in the documentation for `a_func`. This documentation is inserted by Rustdoc and cannot be manually edited by the crate author.
+
+
+## How to use this feature
+
+This feature is unstable, so you can enable it by calling Rustdoc with the unstable `rustdoc-scrape-examples` flag:
+
+```bash
+cargo doc -Zunstable-options -Zrustdoc-scrape-examples=examples
+```
+
+To enable this feature on [docs.rs](https://docs.rs), add this to your Cargo.toml:
+
+```toml
+[package.metadata.docs.rs]
+cargo-args = ["-Zunstable-options", "-Zrustdoc-scrape-examples=examples"]
+```
+
+
+## How it works
+
+When you run `cargo doc`, Rustdoc will analyze all the crates that match Cargo's `--examples` filter for instances of items being documented. Then Rustdoc will include the source code of these instances in the generated documentation.
+
+Rustdoc has a few techniques to ensure these examples don't overwhelm documentation readers, and that it doesn't blow up the page size:
+
+1. For a given item, a maximum of 5 examples are included in the page. The remaining examples are just links to source code.
+2. Only one example is shown by default, and the remaining examples are hidden behind a toggle.
+3. For a given file that contains examples, only the item containing the examples will be included in the generated documentation.
+
+For a given item, Rustdoc sorts its examples based on the size of the example — smaller ones are shown first.
+
+
+## FAQ
+
+### My example is not showing up in the documentation
+
+This feature uses Cargo's convention for finding examples. You should ensure that `cargo check --examples` includes your example file.