Rollup merge of rust-lang#95813 - Urgau:rustdoc-where-clause-space, r=GuillaumeGomez

Remove extra space before a where clause

Remove extra space before where clause in the generated documentation.

The fix is to move the space before the break-line so that it doesn't appear visually but is still here. Removing it completely would create things like this `impl<D> Delta<D>where D: MyTrait` (missing a space before the where) which I don't think we want.

Added two regression test, first one test that the `<br>` is after the space and the second check that the `<br>` is before the spaces.

Before:
![image](https://user-images.githubusercontent.com/3616612/162475212-d4bb6727-ed66-4a55-a4a2-4f55189bf8bd.png)

After:
![image](https://user-images.githubusercontent.com/3616612/162475467-508fd082-60a7-4a8c-b693-8b188e8843e6.png)

r? ``@GuillaumeGomez``

Author: Dylan-DPC

src/librustdoc/html/format.rs

@@ -371,7 +371,8 @@ crate fn print_where_clause<'a, 'tcx: 'a>(
             clause = clause.replace("<br>", &format!("<br>{}", padding));
             clause.insert_str(0, &"&nbsp;".repeat(indent.saturating_sub(1)));
             if !end_newline {
-                clause.insert_str(0, "<br>");
+                // we insert the <br> after a single space but before multiple spaces at the start
+                clause.insert_str(if indent == 0 { 1 } else { 0 }, "<br>");
             }
         }
         write!(f, "{}", clause)

src/test/rustdoc/where.SWhere_Simd_item-decl.html

@@ -0,0 +1 @@
+<div class="docblock item-decl"><pre class="rust struct"><code>pub struct Simd&lt;T, const LANES:&#160;<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>&gt;(_) <br /><span class="where">where<br />&#160;&#160;&#160;&#160;T: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>;</code></pre></div>

src/test/rustdoc/where.SWhere_TraitWhere_item-decl.html

@@ -0,0 +1,3 @@
+<div class="docblock item-decl"><pre class="rust trait"><code>pub trait TraitWhere {
+    type <a href="#associatedtype.Item" class="associatedtype">Item</a>&lt;'a&gt;<br />&#160;&#160;&#160; <span class="where">where<br />&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;Self: 'a</span>;
+}</code></pre></div>

src/test/rustdoc/where.rs

@@ -1,3 +1,4 @@
+#![feature(generic_associated_types)]
 #![crate_name = "foo"]
 
 pub trait MyTrait { fn dummy(&self) { } }
@@ -19,6 +20,18 @@ impl<D> Delta<D> where D: MyTrait {
 
 pub struct Echo<E>(E);
 
+// @has 'foo/struct.Simd.html'
+// @snapshot SWhere_Simd_item-decl - '//div[@class="docblock item-decl"]'
+pub struct Simd<T, const LANES: usize>([T; LANES])
+where
+    T: Sized;
+
+// @has 'foo/trait.TraitWhere.html'
+// @snapshot SWhere_TraitWhere_item-decl - '//div[@class="docblock item-decl"]'
+pub trait TraitWhere {
+    type Item<'a> where Self: 'a;
+}
+
 // @has foo/struct.Echo.html '//*[@class="impl has-srclink"]//h3[@class="code-header in-band"]' \
 //          "impl<E> MyTrait for Echo<E> where E: MyTrait"
 // @has foo/trait.MyTrait.html '//*[@id="implementors-list"]//h3[@class="code-header in-band"]' \