Pass correct line number for indented code blocks.

Author: bdalrhm

Diff for: src/librustdoc/html/markdown.rs

@@ -689,6 +689,12 @@ crate fn find_testable_code<T: doctest::Tester>(
                     .join("\n");
 
                 nb_lines += doc[prev_offset..offset.start].lines().count();
+                // If there are characters between the preceding line ending and
+                // this code block, `str::lines` will return an additional line,
+                // which we subtract here.
+                if nb_lines != 0 && !&doc[prev_offset..offset.start].ends_with("\n") {
+                    nb_lines -= 1;
+                }
                 let line = tests.get_line() + nb_lines + 1;
                 tests.add_test(text, block_info, line);
                 prev_offset = offset.start;

Diff for: src/librustdoc/html/markdown/tests.rs

@@ -1,4 +1,4 @@
-use super::{plain_text_summary, short_markdown_summary};
+use super::{find_testable_code, plain_text_summary, short_markdown_summary};
 use super::{ErrorCodes, IdMap, Ignore, LangString, Markdown, MarkdownHtml};
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
 
@@ -298,3 +298,25 @@ fn test_markdown_html_escape() {
     t("Struct<'a, T>", "<p>Struct&lt;’a, T&gt;</p>\n");
     t("Struct<br>", "<p>Struct&lt;br&gt;</p>\n");
 }
+
+#[test]
+fn test_find_testable_code_line() {
+    fn t(input: &str, expect: &[usize]) {
+        impl crate::doctest::Tester for Vec<usize> {
+            fn add_test(&mut self, _test: String, _config: LangString, line: usize) {
+                self.push(line);
+            }
+        }
+        let mut lines = Vec::<usize>::new();
+        find_testable_code(input, &mut lines, ErrorCodes::No, false, None);
+        assert_eq!(lines, expect);
+    }
+
+    t("", &[]);
+    t("```rust\n```", &[1]);
+    t(" ```rust\n```", &[1]);
+    t("\n```rust\n```", &[2]);
+    t("\n ```rust\n```", &[2]);
+    t("```rust\n```\n```rust\n```", &[1, 3]);
+    t("```rust\n```\n ```rust\n```", &[1, 3]);
+}