Auto merge of #41084 - QuietMisdreavus:rustdoc-format-redux, r=frewsxcxv,GuillaumeGomez

rustdoc: update formatting of fn signatures and where clauses to match style rfcs

Recent updates to style RFCs ([where clauses](https://github.com/rust-lang-nursery/fmt-rfcs/issues/38), [function definitions](https://github.com/rust-lang-nursery/fmt-rfcs/issues/39)) changed the "canonical" style for these items, so this is a rustdoc update to make it emit that style where necessary. This is mainly a conversion from visual indent to block indent, which helps out in situations where there was excessive indent causing lines to wrap regardless.

Samples:

![std::iter::IntoIterator](https://cloud.githubusercontent.com/assets/5217170/24712947/e586604c-19e9-11e7-87ae-4fe64d689dc3.png)

![excerpt from std::iter::Iterator](https://cloud.githubusercontent.com/assets/5217170/24713209/91e65112-19ea-11e7-9ff8-d4cf6b31aae1.png)

![std::iter::FromIterator](https://cloud.githubusercontent.com/assets/5217170/24713138/59f36114-19ea-11e7-9dbb-5f5ba7126e2e.png)

![std::cmp::min](https://cloud.githubusercontent.com/assets/5217170/24713038/1bab88b4-19ea-11e7-935d-defed5648de4.png)

![some trait impls on std::collections::HashMap](https://cloud.githubusercontent.com/assets/5217170/24713251/b7ef69e8-19ea-11e7-94a7-e01fbf89fa31.png)

![`fn extract_code_blocks`, an example given in #40687](https://cloud.githubusercontent.com/assets/5217170/24713159/672717cc-19ea-11e7-9acb-6ac278b90339.png)

![excerpt from itertools::Itertools](https://cloud.githubusercontent.com/assets/5217170/24713323/f06716ea-19ea-11e7-94cc-6ef68d9980ec.png)

fixes #41025 and #40687

r? @rust-lang/docs

1 files changed, 55 insertions, 58 deletions

diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 1e1202f0400..42a18345681 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -2016,13 +2016,13 @@ fn item_function(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
         UnstableFeatures::Allow => f.constness,
         _ => hir::Constness::NotConst
     };
-    let indent = format!("{}{}{}{:#}fn {}{:#}",
-                         VisSpace(&it.visibility),
-                         ConstnessSpace(vis_constness),
-                         UnsafetySpace(f.unsafety),
-                         AbiSpace(f.abi),
-                         it.name.as_ref().unwrap(),
-                         f.generics).len();
+    let name_len = format!("{}{}{}{:#}fn {}{:#}",
+                           VisSpace(&it.visibility),
+                           ConstnessSpace(vis_constness),
+                           UnsafetySpace(f.unsafety),
+                           AbiSpace(f.abi),
+                           it.name.as_ref().unwrap(),
+                           f.generics).len();
     write!(w, "<pre class='rust fn'>")?;
     render_attributes(w, it)?;
     write!(w, "{vis}{constness}{unsafety}{abi}fn \
@@ -2033,8 +2033,12 @@ fn item_function(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
            abi = AbiSpace(f.abi),
            name = it.name.as_ref().unwrap(),
            generics = f.generics,
-           where_clause = WhereClause(&f.generics, 2),
-           decl = Method(&f.decl, indent))?;
+           where_clause = WhereClause { gens: &f.generics, indent: 0, end_newline: true },
+           decl = Method {
+               decl: &f.decl,
+               name_len: name_len,
+               indent: 0,
+           })?;
     document(w, cx, it)
 }
 
@@ -2062,14 +2066,18 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
     // Output the trait definition
     write!(w, "<pre class='rust trait'>")?;
     render_attributes(w, it)?;
-    write!(w, "{}{}trait {}{}{}{} ",
+    write!(w, "{}{}trait {}{}{}",
            VisSpace(&it.visibility),
            UnsafetySpace(t.unsafety),
            it.name.as_ref().unwrap(),
            t.generics,
-           bounds,
-           // Where clauses in traits are indented nine spaces, per rustdoc.css
-           WhereClause(&t.generics, 9))?;
+           bounds)?;
+
+    if !t.generics.where_predicates.is_empty() {
+        write!(w, "{}", WhereClause { gens: &t.generics, indent: 0, end_newline: true })?;
+    } else {
+        write!(w, " ")?;
+    }
 
     let types = t.items.iter().filter(|m| m.is_associated_type()).collect::<Vec<_>>();
     let consts = t.items.iter().filter(|m| m.is_associated_const()).collect::<Vec<_>>();
@@ -2108,7 +2116,14 @@ fn item_trait(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
         for m in &provided {
             write!(w, "    ")?;
             render_assoc_item(w, m, AssocItemLink::Anchor(None), ItemType::Trait)?;
-            write!(w, " {{ ... }}\n")?;
+            match m.inner {
+                clean::MethodItem(ref inner) if !inner.generics.where_predicates.is_empty() => {
+                    write!(w, ",\n    {{ ... }}\n")?;
+                },
+                _ => {
+                    write!(w, " {{ ... }}\n")?;
+                },
+            }
         }
         write!(w, "}}")?;
     }
@@ -2342,21 +2357,17 @@ fn render_assoc_item(w: &mut fmt::Formatter,
         } else {
             hir::Constness::NotConst
         };
-        let prefix = format!("{}{}{:#}fn {}{:#}",
-                             ConstnessSpace(vis_constness),
-                             UnsafetySpace(unsafety),
-                             AbiSpace(abi),
-                             name,
-                             *g);
-        let mut indent = prefix.len();
-        let where_indent = if parent == ItemType::Trait {
-            indent += 4;
-            8
-        } else if parent == ItemType::Impl {
-            2
+        let mut head_len = format!("{}{}{:#}fn {}{:#}",
+                                   ConstnessSpace(vis_constness),
+                                   UnsafetySpace(unsafety),
+                                   AbiSpace(abi),
+                                   name,
+                                   *g).len();
+        let (indent, end_newline) = if parent == ItemType::Trait {
+            head_len += 4;
+            (4, false)
         } else {
-            let prefix = prefix + &format!("{:#}", Method(d, indent));
-            prefix.lines().last().unwrap().len() + 1
+            (0, true)
         };
         write!(w, "{}{}{}fn <a href='{href}' class='fnname'>{name}</a>\
                    {generics}{decl}{where_clause}",
@@ -2366,8 +2377,16 @@ fn render_assoc_item(w: &mut fmt::Formatter,
                href = href,
                name = name,
                generics = *g,
-               decl = Method(d, indent),
-               where_clause = WhereClause(g, where_indent))
+               decl = Method {
+                   decl: d,
+                   name_len: head_len,
+                   indent: indent,
+               },
+               where_clause = WhereClause {
+                   gens: g,
+                   indent: indent,
+                   end_newline: end_newline,
+               })
     }
     match item.inner {
         clean::StrippedItem(..) => Ok(()),
@@ -2480,15 +2499,11 @@ fn item_enum(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
              e: &clean::Enum) -> fmt::Result {
     write!(w, "<pre class='rust enum'>")?;
     render_attributes(w, it)?;
-    let padding = format!("{}enum {}{:#} ",
-                          VisSpace(&it.visibility),
-                          it.name.as_ref().unwrap(),
-                          e.generics).len();
     write!(w, "{}enum {}{}{}",
            VisSpace(&it.visibility),
            it.name.as_ref().unwrap(),
            e.generics,
-           WhereClause(&e.generics, padding))?;
+           WhereClause { gens: &e.generics, indent: 0, end_newline: true })?;
     if e.variants.is_empty() && !e.variants_stripped {
         write!(w, " {{}}")?;
     } else {
@@ -2662,23 +2677,17 @@ fn render_struct(w: &mut fmt::Formatter, it: &clean::Item,
                  fields: &[clean::Item],
                  tab: &str,
                  structhead: bool) -> fmt::Result {
-    let mut plain = String::new();
     write!(w, "{}{}{}",
            VisSpace(&it.visibility),
            if structhead {"struct "} else {""},
            it.name.as_ref().unwrap())?;
-    plain.push_str(&format!("{}{}{}",
-                            VisSpace(&it.visibility),
-                            if structhead {"struct "} else {""},
-                            it.name.as_ref().unwrap()));
     if let Some(g) = g {
-        plain.push_str(&format!("{:#}", g));
         write!(w, "{}", g)?
     }
     match ty {
         doctree::Plain => {
             if let Some(g) = g {
-                write!(w, "{}", WhereClause(g, plain.len() + 1))?
+                write!(w, "{}", WhereClause { gens: g, indent: 0, end_newline: true })?
             }
             let mut has_visible_fields = false;
             write!(w, " {{")?;
@@ -2707,35 +2716,30 @@ fn render_struct(w: &mut fmt::Formatter, it: &clean::Item,
         }
         doctree::Tuple => {
             write!(w, "(")?;
-            plain.push_str("(");
             for (i, field) in fields.iter().enumerate() {
                 if i > 0 {
                     write!(w, ", ")?;
-                    plain.push_str(", ");
                 }
                 match field.inner {
                     clean::StrippedItem(box clean::StructFieldItem(..)) => {
-                        plain.push_str("_");
                         write!(w, "_")?
                     }
                     clean::StructFieldItem(ref ty) => {
-                        plain.push_str(&format!("{}{:#}", VisSpace(&field.visibility), *ty));
                         write!(w, "{}{}", VisSpace(&field.visibility), *ty)?
                     }
                     _ => unreachable!()
                 }
             }
             write!(w, ")")?;
-            plain.push_str(")");
             if let Some(g) = g {
-                write!(w, "{}", WhereClause(g, plain.len() + 1))?
+                write!(w, "{}", WhereClause { gens: g, indent: 0, end_newline: false })?
             }
             write!(w, ";")?;
         }
         doctree::Unit => {
             // Needed for PhantomData.
             if let Some(g) = g {
-                write!(w, "{}", WhereClause(g, plain.len() + 1))?
+                write!(w, "{}", WhereClause { gens: g, indent: 0, end_newline: false })?
             }
             write!(w, ";")?;
         }
@@ -2748,19 +2752,13 @@ fn render_union(w: &mut fmt::Formatter, it: &clean::Item,
                 fields: &[clean::Item],
                 tab: &str,
                 structhead: bool) -> fmt::Result {
-    let mut plain = String::new();
     write!(w, "{}{}{}",
            VisSpace(&it.visibility),
            if structhead {"union "} else {""},
            it.name.as_ref().unwrap())?;
-    plain.push_str(&format!("{}{}{}",
-                            VisSpace(&it.visibility),
-                            if structhead {"union "} else {""},
-                            it.name.as_ref().unwrap()));
     if let Some(g) = g {
         write!(w, "{}", g)?;
-        plain.push_str(&format!("{:#}", g));
-        write!(w, "{}", WhereClause(g, plain.len() + 1))?;
+        write!(w, "{}", WhereClause { gens: g, indent: 0, end_newline: true })?;
     }
 
     write!(w, " {{\n{}", tab)?;
@@ -3059,13 +3057,12 @@ fn render_impl(w: &mut fmt::Formatter, cx: &Context, i: &Impl, link: AssocItemLi
 
 fn item_typedef(w: &mut fmt::Formatter, cx: &Context, it: &clean::Item,
                 t: &clean::Typedef) -> fmt::Result {
-    let indent = format!("type {}{:#} ", it.name.as_ref().unwrap(), t.generics).len();
     write!(w, "<pre class='rust typedef'>")?;
     render_attributes(w, it)?;
     write!(w, "type {}{}{where_clause} = {type_};</pre>",
            it.name.as_ref().unwrap(),
            t.generics,
-           where_clause = WhereClause(&t.generics, indent),
+           where_clause = WhereClause { gens: &t.generics, indent: 0, end_newline: true },
            type_ = t.type_)?;
 
     document(w, cx, it)