Pretty-print macro matchers instead of using source code

The output is not quite as nice as it used to be, but it does work.

src/librustdoc/clean/inline.rs

@@ -13,10 +13,9 @@ use rustc_metadata::creader::LoadedMacro;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Symbol};
-use rustc_span::Span;
 
 use crate::clean::{
-    self, Attributes, AttributesExt, FakeDefId, GetDefId, NestedAttributesExt, ToSource, Type,
+    self, utils, Attributes, AttributesExt, FakeDefId, GetDefId, NestedAttributesExt, Type,
 };
 use crate::core::DocContext;
 use crate::formats::item_type::ItemType;
@@ -547,23 +546,20 @@ fn build_macro(cx: &mut DocContext<'_>, did: DefId, name: Symbol) -> clean::Item
     let imported_from = cx.tcx.crate_name(did.krate);
     match cx.enter_resolver(|r| r.cstore().load_macro_untracked(did, cx.sess())) {
         LoadedMacro::MacroDef(def, _) => {
-            let matchers: Vec<Span> = if let ast::ItemKind::MacroDef(ref def) = def.kind {
+            if let ast::ItemKind::MacroDef(ref def) = def.kind {
                 let tts: Vec<_> = def.body.inner_tokens().into_trees().collect();
-                tts.chunks(4).map(|arm| arm[0].span()).collect()
-            } else {
-                unreachable!()
-            };
+                let matchers = tts.chunks(4).map(|arm| &arm[0]);
 
-            let source = format!(
-                "macro_rules! {} {{\n{}}}",
-                name.clean(cx),
-                matchers
-                    .iter()
-                    .map(|span| { format!("    {} => {{ ... }};\n", span.to_src(cx)) })
-                    .collect::<String>()
-            );
+                let source = format!(
+                    "macro_rules! {} {{\n{}}}",
+                    name.clean(cx),
+                    utils::render_macro_arms(matchers, ";")
+                );
 
-            clean::MacroItem(clean::Macro { source, imported_from: Some(imported_from) })
+                clean::MacroItem(clean::Macro { source, imported_from: Some(imported_from) })
+            } else {
+                unreachable!()
+            }
         }
         LoadedMacro::ProcMacro(ext) => clean::ProcMacroItem(clean::ProcMacro {
             kind: ext.macro_kind(),

src/librustdoc/clean/mod.rs

@@ -2172,17 +2172,11 @@ impl Clean<Item> for (&hir::MacroDef<'_>, Option<Symbol>) {
         let (item, renamed) = self;
         let name = renamed.unwrap_or(item.ident.name);
         let tts = item.ast.body.inner_tokens().trees().collect::<Vec<_>>();
-        // Extract the spans of all matchers. They represent the "interface" of the macro.
-        let matchers = tts.chunks(4).map(|arm| arm[0].span()).collect::<Vec<_>>();
+        // Extract the macro's matchers. They represent the "interface" of the macro.
+        let matchers = tts.chunks(4).map(|arm| &arm[0]);
+
         let source = if item.ast.macro_rules {
-            format!(
-                "macro_rules! {} {{\n{}}}",
-                name,
-                matchers
-                    .iter()
-                    .map(|span| { format!("    {} => {{ ... }};\n", span.to_src(cx)) })
-                    .collect::<String>(),
-            )
+            format!("macro_rules! {} {{\n{}}}", name, render_macro_arms(matchers, ";"))
         } else {
             let vis = item.vis.clean(cx);
             let def_id = item.def_id.to_def_id();
@@ -2192,17 +2186,14 @@ impl Clean<Item> for (&hir::MacroDef<'_>, Option<Symbol>) {
                     "{}macro {}{} {{\n    ...\n}}",
                     vis.to_src_with_space(cx.tcx, def_id),
                     name,
-                    matchers.iter().map(|span| span.to_src(cx)).collect::<String>(),
+                    matchers.map(render_macro_matcher).collect::<String>(),
                 )
             } else {
                 format!(
                     "{}macro {} {{\n{}}}",
                     vis.to_src_with_space(cx.tcx, def_id),
                     name,
-                    matchers
-                        .iter()
-                        .map(|span| { format!("    {} => {{ ... }},\n", span.to_src(cx)) })
-                        .collect::<String>(),
+                    render_macro_arms(matchers, ","),
                 )
             }
         };

src/librustdoc/clean/utils.rs

@@ -7,13 +7,15 @@ use crate::clean::{
 use crate::core::DocContext;
 use crate::formats::item_type::ItemType;
 
+use rustc_ast::tokenstream::TokenTree;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
 use rustc_middle::ty::{self, DefIdTree, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
+use std::fmt::Write as _;
 use std::mem;
 
 #[cfg(test)]
@@ -248,22 +250,6 @@ crate fn build_deref_target_impls(cx: &mut DocContext<'_>, items: &[Item], ret:
     }
 }
 
-crate trait ToSource {
-    fn to_src(&self, cx: &DocContext<'_>) -> String;
-}
-
-impl ToSource for rustc_span::Span {
-    fn to_src(&self, cx: &DocContext<'_>) -> String {
-        debug!("converting span {:?} to snippet", self);
-        let sn = match cx.sess().source_map().span_to_snippet(*self) {
-            Ok(x) => x,
-            Err(_) => String::new(),
-        };
-        debug!("got snippet {}", sn);
-        sn
-    }
-}
-
 crate fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
     use rustc_hir::*;
     debug!("trying to get a name from pattern: {:?}", p);
@@ -572,3 +558,22 @@ crate fn has_doc_flag(attrs: ty::Attributes<'_>, flag: Symbol) -> bool {
 ///
 /// Set by `bootstrap::Builder::doc_rust_lang_org_channel` in order to keep tests passing on beta/stable.
 crate const DOC_RUST_LANG_ORG_CHANNEL: &'static str = env!("DOC_RUST_LANG_ORG_CHANNEL");
+
+/// Render a sequence of macro arms in a format suitable for displaying to the user
+/// as part of an item declaration.
+pub(super) fn render_macro_arms<'a>(
+    matchers: impl Iterator<Item = &'a TokenTree>,
+    arm_delim: &str,
+) -> String {
+    let mut out = String::new();
+    for matcher in matchers {
+        writeln!(out, "    {} => {{ ... }}{}", render_macro_matcher(matcher), arm_delim).unwrap();
+    }
+    out
+}
+
+/// Render a macro matcher in a format suitable for displaying to the user
+/// as part of an item declaration.
+pub(super) fn render_macro_matcher(matcher: &TokenTree) -> String {
+    rustc_ast_pretty::pprust::tt_to_string(matcher)
+}

src/test/rustdoc/decl_macro.rs

@@ -9,7 +9,7 @@ pub macro my_macro() {
 
 }
 
-// @has decl_macro/macro.my_macro_2.html //pre 'pub macro my_macro_2($($tok:tt)*) {'
+// @has decl_macro/macro.my_macro_2.html //pre 'pub macro my_macro_2($ ($ tok : tt) *) {'
 // @has - //pre '...'
 // @has - //pre '}'
 pub macro my_macro_2($($tok:tt)*) {
@@ -18,8 +18,8 @@ pub macro my_macro_2($($tok:tt)*) {
 
 // @has decl_macro/macro.my_macro_multi.html //pre 'pub macro my_macro_multi {'
 // @has - //pre '(_) => { ... },'
-// @has - //pre '($foo:ident . $bar:expr) => { ... },'
-// @has - //pre '($($foo:literal),+) => { ... }'
+// @has - //pre '($ foo : ident.$ bar : expr) => { ... },'
+// @has - //pre '($ ($ foo : literal), +) => { ... },'
 // @has - //pre '}'
 pub macro my_macro_multi {
     (_) => {
@@ -33,7 +33,7 @@ pub macro my_macro_multi {
     }
 }
 
-// @has decl_macro/macro.by_example_single.html //pre 'pub macro by_example_single($foo:expr) {'
+// @has decl_macro/macro.by_example_single.html //pre 'pub macro by_example_single($ foo : expr) {'
 // @has - //pre '...'
 // @has - //pre '}'
 pub macro by_example_single {
@@ -42,12 +42,12 @@ pub macro by_example_single {
 
 mod a {
     mod b {
-        // @has decl_macro/a/b/macro.by_example_vis.html //pre 'pub(super) macro by_example_vis($foo:expr) {'
+        // @has decl_macro/a/b/macro.by_example_vis.html //pre 'pub(super) macro by_example_vis($ foo : expr) {'
         pub(in super) macro by_example_vis {
             ($foo:expr) => {}
         }
         mod c {
-            // @has decl_macro/a/b/c/macro.by_example_vis_named.html //pre 'pub(in a) macro by_example_vis_named($foo:expr) {'
+            // @has decl_macro/a/b/c/macro.by_example_vis_named.html //pre 'pub(in a) macro by_example_vis_named($ foo : expr) {'
             pub(in a) macro by_example_vis_named {
                 ($foo:expr) => {}
             }

src/test/rustdoc/macro_rules-matchers.rs

@@ -7,16 +7,15 @@
 // @has - '//span[@class="macro"]' 'macro_rules!'
 // @has - '//span[@class="ident"]' 'todo'
 // Note: count = 2 * ('=' + '>') + '+' = 2 * (1 + 1) + 1 = 5
-// @count - '//span[@class="op"]' 5
+// @count - '//pre[@class="rust macro"]//span[@class="op"]' 5
 
 // @has - '{ ()'
 // @has - '//span[@class="op"]' '='
 // @has - '//span[@class="op"]' '>'
 // @has - '{ ... };'
 
-// @has - '($('
-// @has - '//span[@class="macro-nonterminal"]' '$'
-// @has - '//span[@class="macro-nonterminal"]' 'arg'
+// @has - '($ ($'
+// @has - '//span[@class="ident"]' 'arg'
 // @has - ':'
 // @has - '//span[@class="ident"]' 'tt'
 // @has - '//span[@class="op"]' '+'
@@ -28,7 +27,7 @@ mod mod1 {
     // @has - 'macro_rules!'
     // @has - 'macro1'
     // @has - '{ ()'
-    // @has - '($('
+    // @has - '($ ('
     // @has - 'arg'
     // @has - 'expr'
     // @has - ','

src/test/rustdoc/macros.rs

@@ -1,7 +1,7 @@
 // @has macros/macro.my_macro.html //pre 'macro_rules! my_macro {'
 // @has - //pre '() => { ... };'
-// @has - //pre '($a:tt) => { ... };'
-// @has - //pre '($e:expr) => { ... };'
+// @has - //pre '($ a : tt) => { ... };'
+// @has - //pre '($ e : expr) => { ... };'
 #[macro_export]
 macro_rules! my_macro {
     () => [];
@@ -12,8 +12,8 @@ macro_rules! my_macro {
 // Check that exported macro defined in a module are shown at crate root.
 // @has macros/macro.my_sub_macro.html //pre 'macro_rules! my_sub_macro {'
 // @has - //pre '() => { ... };'
-// @has - //pre '($a:tt) => { ... };'
-// @has - //pre '($e:expr) => { ... };'
+// @has - //pre '($ a : tt) => { ... };'
+// @has - //pre '($ e : expr) => { ... };'
 mod sub {
     #[macro_export]
     macro_rules! my_sub_macro {