Improve Rustdoc UI for scraped examples with multiline arguments, fix

overflow in line numbers

src/librustdoc/html/render/mod.rs

@@ -2717,6 +2717,30 @@ fn render_call_locations(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item) {
         // The output code is limited to that byte range.
         let contents_subset = &contents[(byte_min as usize)..(byte_max as usize)];
 
+        // Given a call-site range, return the set of sub-ranges that exclude leading whitespace
+        // when the range spans multiple lines.
+        let strip_leading_whitespace = |(lo, hi): (u32, u32)| -> Vec<(u32, u32)> {
+            let contents_range = &contents_subset[(lo as usize)..(hi as usize)];
+            let mut ignoring_whitespace = false;
+            let mut ranges = Vec::new();
+            let mut cur_lo = 0;
+            for (idx, chr) in contents_range.char_indices() {
+                let idx = idx as u32;
+                if ignoring_whitespace {
+                    if !chr.is_whitespace() {
+                        ignoring_whitespace = false;
+                        cur_lo = idx;
+                    }
+                } else if chr == '\n' {
+                    ranges.push((lo + cur_lo, lo + idx));
+                    cur_lo = idx;
+                    ignoring_whitespace = true;
+                }
+            }
+            ranges.push((lo + cur_lo, hi));
+            ranges
+        };
+
         // The call locations need to be updated to reflect that the size of the program has changed.
         // Specifically, the ranges are all subtracted by `byte_min` since that's the new zero point.
         let (mut byte_ranges, line_ranges): (Vec<_>, Vec<_>) = call_data
@@ -2726,10 +2750,12 @@ fn render_call_locations(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item) {
                 let (byte_lo, byte_hi) = loc.call_expr.byte_span;
                 let (line_lo, line_hi) = loc.call_expr.line_span;
                 let byte_range = (byte_lo - byte_min, byte_hi - byte_min);
+                let byte_ranges = strip_leading_whitespace(byte_range);
+
                 let line_range = (line_lo - line_min, line_hi - line_min);
                 let (line_url, line_title) = link_to_loc(call_data, loc);
 
-                (byte_range, (line_range, line_url, line_title))
+                (byte_ranges, (line_range, line_url, line_title))
             })
             .unzip();
 
@@ -2784,8 +2810,8 @@ fn render_call_locations(w: &mut Buffer, cx: &Context<'_>, item: &clean::Item) {
         let root_path = vec!["../"; cx.current.len() - 1].join("");
 
         let mut decoration_info = FxHashMap::default();
-        decoration_info.insert("highlight focus", vec![byte_ranges.remove(0)]);
-        decoration_info.insert("highlight", byte_ranges);
+        decoration_info.insert("highlight focus", byte_ranges.remove(0));
+        decoration_info.insert("highlight", byte_ranges.into_iter().flatten().collect());
 
         sources::print_src(
             w,

src/librustdoc/html/static/css/rustdoc.css

@@ -2038,17 +2038,16 @@ details.rustdoc-toggle[open] > summary.hideme::after {
 	font-family: 'Fira Sans';
 }
 
-.scraped-example:not(.expanded) .code-wrapper pre.line-numbers {
-	overflow: hidden;
-	max-height: 240px;
-}
-
-.scraped-example:not(.expanded) .code-wrapper .example-wrap pre.rust {
+.scraped-example:not(.expanded) .code-wrapper pre {
 	overflow-y: hidden;
 	max-height: 240px;
 	padding-bottom: 0;
 }
 
+.scraped-example:not(.expanded) .code-wrapper pre.line-numbers {
+	overflow-x: hidden;
+}
+
 .scraped-example .code-wrapper .prev {
 	position: absolute;
 	top: 0.25em;

src/librustdoc/html/static/js/scrape-examples.js

@@ -1,14 +1,28 @@
 /* global addClass, hasClass, removeClass, onEach */
 
 (function () {
-    // Scroll code block to put the given code location in the middle of the viewer
+    // Number of lines shown when code viewer is not expanded
+    const MAX_LINES = 10;
+
+    // Scroll code block to the given code location
     function scrollToLoc(elt, loc) {
-        var wrapper = elt.querySelector(".code-wrapper");
-        var halfHeight = wrapper.offsetHeight / 2;
         var lines = elt.querySelector('.line-numbers');
-        var offsetMid = (lines.children[loc[0]].offsetTop
-                         + lines.children[loc[1]].offsetTop) / 2;
-        var scrollOffset = offsetMid - halfHeight;
+        var scrollOffset;
+
+        // If the block is greater than the size of the viewer,
+        // then scroll to the top of the block. Otherwise scroll
+        // to the middle of the block.
+        if (loc[1] - loc[0] > MAX_LINES) {
+            var line = Math.max(0, loc[0] - 1);
+            scrollOffset = lines.children[line].offsetTop;
+        } else {
+            var wrapper = elt.querySelector(".code-wrapper");
+            var halfHeight = wrapper.offsetHeight / 2;
+            var offsetMid = (lines.children[loc[0]].offsetTop
+                             + lines.children[loc[1]].offsetTop) / 2;
+            scrollOffset = offsetMid - halfHeight;
+        }
+
         lines.scrollTo(0, scrollOffset);
         elt.querySelector(".rust").scrollTo(0, scrollOffset);
     }