Change handling of spans in scrape examples, add test for highlight decorations

Author: willcrichton

src/librustdoc/html/highlight/fixtures/decorations.html

@@ -0,0 +1,2 @@
+<span class="example"><span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="number">1</span>;</span>
+<span class="kw">let</span> <span class="ident">y</span> <span class="op">=</span> <span class="number">2</span>;

src/librustdoc/html/highlight/tests.rs

@@ -1,6 +1,7 @@
-use super::write_code;
+use super::{write_code, DecorationInfo};
 use crate::html::format::Buffer;
 use expect_test::expect_file;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_span::create_default_session_globals_then;
 use rustc_span::edition::Edition;
 
@@ -64,3 +65,17 @@ fn test_union_highlighting() {
         expect_file!["fixtures/union.html"].assert_eq(&html.into_inner());
     });
 }
+
+#[test]
+fn test_decorations() {
+    create_default_session_globals_then(|| {
+        let src = "let x = 1;
+let y = 2;";
+        let mut decorations = FxHashMap::default();
+        decorations.insert("example", vec![(0, 10)]);
+
+        let mut html = Buffer::new();
+        write_code(&mut html, src, Edition::Edition2018, None, Some(DecorationInfo(decorations)));
+        expect_file!["fixtures/decorations.html"].assert_eq(&html.into_inner());
+    });
+}

src/librustdoc/scrape_examples.rs

@@ -149,9 +149,11 @@ where
             }
         };
 
-        // We need to get the file the example originates in. If the call is contained
-        // in a macro, then trace the span back to the macro source (rather than macro definition).
-        let span = span.source_callsite();
+        // If this span comes from a macro expansion, then the source code may not actually show
+        // a use of the given item, so it would be a poor example. Hence, we skip all uses in macros.
+        if span.from_expansion() {
+            return;
+        }
 
         // Save call site if the function resolves to a concrete definition
         if let ty::FnDef(def_id, _) = ty.kind() {