Fix sidebar scroll position when heading nav is involved

This fixes an issue where the sidebar was scrolling incorrectly when
clicking on chapters when a heading nav is currently in view. The
problem was that it was storing the scrollTop of the sidebar, but it was
not considering that when navigating to another chapter that the heading
nav of the previous chapter would disappear.

The solution is to keep of an offset instead so that it can make sure
that the vertical position of the clicked chapter stays in the same
relative position when the new page loads.

Fixes https://github.com/rust-lang/mdBook/issues/2967

crates/mdbook-html/front-end/templates/toc.js.hbs

@@ -40,14 +40,22 @@ class MDBookSidebarScrollbox extends HTMLElement {
         // Track and set sidebar scroll position
         this.addEventListener('click', e => {
             if (e.target.tagName === 'A') {
-                sessionStorage.setItem('sidebar-scroll', this.scrollTop);
+                const clientRect = e.target.getBoundingClientRect();
+                const sidebarRect = this.getBoundingClientRect();
+                sessionStorage.setItem('sidebar-scroll-offset', clientRect.top - sidebarRect.top);
             }
         }, { passive: true });
-        const sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
-        sessionStorage.removeItem('sidebar-scroll');
-        if (sidebarScrollTop) {
+        const sidebarScrollOffset = sessionStorage.getItem('sidebar-scroll-offset');
+        sessionStorage.removeItem('sidebar-scroll-offset');
+        if (sidebarScrollOffset !== null) {
             // preserve sidebar scroll position when navigating via links within sidebar
-            this.scrollTop = sidebarScrollTop;
+            const activeSection = this.querySelector('.active');
+            if (activeSection) {
+                const clientRect = activeSection.getBoundingClientRect();
+                const sidebarRect = this.getBoundingClientRect();
+                const currentOffset = clientRect.top - sidebarRect.top;
+                this.scrollTop += currentOffset - parseFloat(sidebarScrollOffset);
+            }
         } else {
             // scroll sidebar to current active section when navigating via
             // 'next/previous chapter' buttons

tests/gui/books/sidebar-scroll/book.toml

@@ -0,0 +1,3 @@
+[book]
+title = "sidebar-scroll"
+language = "en"

tests/gui/books/sidebar-scroll/src/SUMMARY.md

@@ -0,0 +1,102 @@
+# Summary
+
+- [Chapter 1](./chapter_1.md)
+- [Chapter 2](./chapter_2.md)
+- [Chapter 3](./chapter_3.md)
+- [Chapter 4](./chapter_4.md)
+- [Chapter 5](./chapter_5.md)
+- [Chapter 6](./chapter_6.md)
+- [Chapter 7](./chapter_7.md)
+- [Chapter 8](./chapter_8.md)
+- [Chapter 9](./chapter_9.md)
+- [Chapter 10](./chapter_10.md)
+- [Chapter 11](./chapter_11.md)
+- [Chapter 12](./chapter_12.md)
+- [Chapter 13](./chapter_13.md)
+- [Chapter 14](./chapter_14.md)
+- [Chapter 15](./chapter_15.md)
+- [Chapter 16](./chapter_16.md)
+- [Chapter 17](./chapter_17.md)
+- [Chapter 18](./chapter_18.md)
+- [Chapter 19](./chapter_19.md)
+- [Chapter 20](./chapter_20.md)
+- [Chapter 21](./chapter_21.md)
+- [Chapter 22](./chapter_22.md)
+- [Chapter 23](./chapter_23.md)
+- [Chapter 24](./chapter_24.md)
+- [Chapter 25](./chapter_25.md)
+- [Chapter 26](./chapter_26.md)
+- [Chapter 27](./chapter_27.md)
+- [Chapter 28](./chapter_28.md)
+- [Chapter 29](./chapter_29.md)
+- [Chapter 30](./chapter_30.md)
+- [Chapter 31](./chapter_31.md)
+- [Chapter 32](./chapter_32.md)
+- [Chapter 33](./chapter_33.md)
+- [Chapter 34](./chapter_34.md)
+- [Chapter 35](./chapter_35.md)
+- [Chapter 36](./chapter_36.md)
+- [Chapter 37](./chapter_37.md)
+- [Chapter 38](./chapter_38.md)
+- [Chapter 39](./chapter_39.md)
+- [Chapter 40](./chapter_40.md)
+- [Chapter 41](./chapter_41.md)
+- [Chapter 42](./chapter_42.md)
+- [Chapter 43](./chapter_43.md)
+- [Chapter 44](./chapter_44.md)
+- [Chapter 45](./chapter_45.md)
+- [Chapter 46](./chapter_46.md)
+- [Chapter 47](./chapter_47.md)
+- [Chapter 48](./chapter_48.md)
+- [Chapter 49](./chapter_49.md)
+- [Chapter 50](./chapter_50.md)
+- [Chapter 51](./chapter_51.md)
+- [Chapter 52](./chapter_52.md)
+- [Chapter 53](./chapter_53.md)
+- [Chapter 54](./chapter_54.md)
+- [Chapter 55](./chapter_55.md)
+- [Chapter 56](./chapter_56.md)
+- [Chapter 57](./chapter_57.md)
+- [Chapter 58](./chapter_58.md)
+- [Chapter 59](./chapter_59.md)
+- [Chapter 60](./chapter_60.md)
+- [Chapter 61](./chapter_61.md)
+- [Chapter 62](./chapter_62.md)
+- [Chapter 63](./chapter_63.md)
+- [Chapter 64](./chapter_64.md)
+- [Chapter 65](./chapter_65.md)
+- [Chapter 66](./chapter_66.md)
+- [Chapter 67](./chapter_67.md)
+- [Chapter 68](./chapter_68.md)
+- [Chapter 69](./chapter_69.md)
+- [Chapter 70](./chapter_70.md)
+- [Chapter 71](./chapter_71.md)
+- [Chapter 72](./chapter_72.md)
+- [Chapter 73](./chapter_73.md)
+- [Chapter 74](./chapter_74.md)
+- [Chapter 75](./chapter_75.md)
+- [Chapter 76](./chapter_76.md)
+- [Chapter 77](./chapter_77.md)
+- [Chapter 78](./chapter_78.md)
+- [Chapter 79](./chapter_79.md)
+- [Chapter 80](./chapter_80.md)
+- [Chapter 81](./chapter_81.md)
+- [Chapter 82](./chapter_82.md)
+- [Chapter 83](./chapter_83.md)
+- [Chapter 84](./chapter_84.md)
+- [Chapter 85](./chapter_85.md)
+- [Chapter 86](./chapter_86.md)
+- [Chapter 87](./chapter_87.md)
+- [Chapter 88](./chapter_88.md)
+- [Chapter 89](./chapter_89.md)
+- [Chapter 90](./chapter_90.md)
+- [Chapter 91](./chapter_91.md)
+- [Chapter 92](./chapter_92.md)
+- [Chapter 93](./chapter_93.md)
+- [Chapter 94](./chapter_94.md)
+- [Chapter 95](./chapter_95.md)
+- [Chapter 96](./chapter_96.md)
+- [Chapter 97](./chapter_97.md)
+- [Chapter 98](./chapter_98.md)
+- [Chapter 99](./chapter_99.md)
+- [Chapter 100](./chapter_100.md)

tests/gui/books/sidebar-scroll/src/chapter_1.md

@@ -0,0 +1,3 @@
+# Chapter 1
+
+## This has a single heading

tests/gui/books/sidebar-scroll/src/chapter_10.md

@@ -0,0 +1,28 @@
+# Chapter 10
+
+## Heading A
+## Heading B
+## Heading C
+## Heading D
+## Heading E
+## Heading F
+## Heading G
+## Heading H
+## Heading I
+## Heading J
+## Heading K
+## Heading L
+## Heading M
+## Heading N
+## Heading O
+## Heading P
+## Heading Q
+## Heading R
+## Heading S
+## Heading T
+## Heading U
+## Heading V
+## Heading W
+## Heading X
+## Heading Y
+## Heading Z

tests/gui/books/sidebar-scroll/src/chapter_100.md

@@ -0,0 +1 @@
+# Chapter 100

tests/gui/books/sidebar-scroll/src/chapter_11.md

@@ -0,0 +1 @@
+# Chapter 11

tests/gui/books/sidebar-scroll/src/chapter_12.md

@@ -0,0 +1 @@
+# Chapter 12

tests/gui/books/sidebar-scroll/src/chapter_13.md

@@ -0,0 +1 @@
+# Chapter 13

tests/gui/books/sidebar-scroll/src/chapter_14.md

@@ -0,0 +1 @@
+# Chapter 14

tests/gui/books/sidebar-scroll/src/chapter_15.md

@@ -0,0 +1 @@
+# Chapter 15

tests/gui/books/sidebar-scroll/src/chapter_16.md

@@ -0,0 +1 @@
+# Chapter 16

tests/gui/books/sidebar-scroll/src/chapter_17.md

@@ -0,0 +1 @@
+# Chapter 17

tests/gui/books/sidebar-scroll/src/chapter_18.md

@@ -0,0 +1 @@
+# Chapter 18

tests/gui/books/sidebar-scroll/src/chapter_19.md

@@ -0,0 +1 @@
+# Chapter 19

tests/gui/books/sidebar-scroll/src/chapter_2.md

@@ -0,0 +1 @@
+# Chapter 2

tests/gui/books/sidebar-scroll/src/chapter_20.md

@@ -0,0 +1 @@
+# Chapter 20

tests/gui/books/sidebar-scroll/src/chapter_21.md

@@ -0,0 +1 @@
+# Chapter 21

tests/gui/books/sidebar-scroll/src/chapter_22.md

@@ -0,0 +1 @@
+# Chapter 22

tests/gui/books/sidebar-scroll/src/chapter_23.md

@@ -0,0 +1 @@
+# Chapter 23

tests/gui/books/sidebar-scroll/src/chapter_24.md

@@ -0,0 +1 @@
+# Chapter 24

tests/gui/books/sidebar-scroll/src/chapter_25.md

@@ -0,0 +1 @@
+# Chapter 25

tests/gui/books/sidebar-scroll/src/chapter_26.md

@@ -0,0 +1 @@
+# Chapter 26

tests/gui/books/sidebar-scroll/src/chapter_27.md

@@ -0,0 +1 @@
+# Chapter 27

tests/gui/books/sidebar-scroll/src/chapter_28.md

@@ -0,0 +1 @@
+# Chapter 28

tests/gui/books/sidebar-scroll/src/chapter_29.md

@@ -0,0 +1 @@
+# Chapter 29

tests/gui/books/sidebar-scroll/src/chapter_3.md

@@ -0,0 +1 @@
+# Chapter 3

tests/gui/books/sidebar-scroll/src/chapter_30.md

@@ -0,0 +1 @@
+# Chapter 30

tests/gui/books/sidebar-scroll/src/chapter_31.md

@@ -0,0 +1 @@
+# Chapter 31

tests/gui/books/sidebar-scroll/src/chapter_32.md

@@ -0,0 +1 @@
+# Chapter 32

tests/gui/books/sidebar-scroll/src/chapter_33.md

@@ -0,0 +1 @@
+# Chapter 33

tests/gui/books/sidebar-scroll/src/chapter_34.md

@@ -0,0 +1 @@
+# Chapter 34

tests/gui/books/sidebar-scroll/src/chapter_35.md

@@ -0,0 +1,28 @@
+# Chapter 35
+
+## Heading A
+## Heading B
+## Heading C
+## Heading D
+## Heading E
+## Heading F
+## Heading G
+## Heading H
+## Heading I
+## Heading J
+## Heading K
+## Heading L
+## Heading M
+## Heading N
+## Heading O
+## Heading P
+## Heading Q
+## Heading R
+## Heading S
+## Heading T
+## Heading U
+## Heading V
+## Heading W
+## Heading X
+## Heading Y
+## Heading Z

tests/gui/books/sidebar-scroll/src/chapter_36.md

@@ -0,0 +1 @@
+# Chapter 36

tests/gui/books/sidebar-scroll/src/chapter_37.md

@@ -0,0 +1 @@
+# Chapter 37

tests/gui/books/sidebar-scroll/src/chapter_38.md

@@ -0,0 +1 @@
+# Chapter 38

tests/gui/books/sidebar-scroll/src/chapter_39.md

@@ -0,0 +1 @@
+# Chapter 39

tests/gui/books/sidebar-scroll/src/chapter_4.md

@@ -0,0 +1 @@
+# Chapter 4

tests/gui/books/sidebar-scroll/src/chapter_40.md

@@ -0,0 +1 @@
+# Chapter 40

tests/gui/books/sidebar-scroll/src/chapter_41.md

@@ -0,0 +1 @@
+# Chapter 41

tests/gui/books/sidebar-scroll/src/chapter_42.md

@@ -0,0 +1 @@
+# Chapter 42

tests/gui/books/sidebar-scroll/src/chapter_43.md

@@ -0,0 +1 @@
+# Chapter 43

tests/gui/books/sidebar-scroll/src/chapter_44.md

@@ -0,0 +1 @@
+# Chapter 44

tests/gui/books/sidebar-scroll/src/chapter_45.md

@@ -0,0 +1 @@
+# Chapter 45

tests/gui/books/sidebar-scroll/src/chapter_46.md

@@ -0,0 +1 @@
+# Chapter 46

tests/gui/books/sidebar-scroll/src/chapter_47.md

@@ -0,0 +1 @@
+# Chapter 47

tests/gui/books/sidebar-scroll/src/chapter_48.md

@@ -0,0 +1 @@
+# Chapter 48

tests/gui/books/sidebar-scroll/src/chapter_49.md

@@ -0,0 +1 @@
+# Chapter 49

tests/gui/books/sidebar-scroll/src/chapter_5.md

@@ -0,0 +1 @@
+# Chapter 5

tests/gui/books/sidebar-scroll/src/chapter_50.md

@@ -0,0 +1 @@
+# Chapter 50

tests/gui/books/sidebar-scroll/src/chapter_51.md

@@ -0,0 +1 @@
+# Chapter 51

tests/gui/books/sidebar-scroll/src/chapter_52.md

@@ -0,0 +1 @@
+# Chapter 52

tests/gui/books/sidebar-scroll/src/chapter_53.md

@@ -0,0 +1 @@
+# Chapter 53

tests/gui/books/sidebar-scroll/src/chapter_54.md

@@ -0,0 +1 @@
+# Chapter 54

tests/gui/books/sidebar-scroll/src/chapter_55.md

@@ -0,0 +1 @@
+# Chapter 55

tests/gui/books/sidebar-scroll/src/chapter_56.md

@@ -0,0 +1 @@
+# Chapter 56

tests/gui/books/sidebar-scroll/src/chapter_57.md

@@ -0,0 +1 @@
+# Chapter 57

tests/gui/books/sidebar-scroll/src/chapter_58.md

@@ -0,0 +1 @@
+# Chapter 58

tests/gui/books/sidebar-scroll/src/chapter_59.md

@@ -0,0 +1 @@
+# Chapter 59

tests/gui/books/sidebar-scroll/src/chapter_6.md

@@ -0,0 +1 @@
+# Chapter 6

tests/gui/books/sidebar-scroll/src/chapter_60.md

@@ -0,0 +1 @@
+# Chapter 60

tests/gui/books/sidebar-scroll/src/chapter_61.md

@@ -0,0 +1 @@
+# Chapter 61

tests/gui/books/sidebar-scroll/src/chapter_62.md

@@ -0,0 +1 @@
+# Chapter 62

tests/gui/books/sidebar-scroll/src/chapter_63.md

@@ -0,0 +1 @@
+# Chapter 63

tests/gui/books/sidebar-scroll/src/chapter_64.md

@@ -0,0 +1 @@
+# Chapter 64

tests/gui/books/sidebar-scroll/src/chapter_65.md

@@ -0,0 +1 @@
+# Chapter 65

tests/gui/books/sidebar-scroll/src/chapter_66.md

@@ -0,0 +1 @@
+# Chapter 66

tests/gui/books/sidebar-scroll/src/chapter_67.md

@@ -0,0 +1 @@
+# Chapter 67

tests/gui/books/sidebar-scroll/src/chapter_68.md

@@ -0,0 +1 @@
+# Chapter 68

tests/gui/books/sidebar-scroll/src/chapter_69.md

@@ -0,0 +1 @@
+# Chapter 69

tests/gui/books/sidebar-scroll/src/chapter_7.md

@@ -0,0 +1 @@
+# Chapter 7

tests/gui/books/sidebar-scroll/src/chapter_70.md

@@ -0,0 +1 @@
+# Chapter 70

tests/gui/books/sidebar-scroll/src/chapter_71.md

@@ -0,0 +1 @@
+# Chapter 71

tests/gui/books/sidebar-scroll/src/chapter_72.md

@@ -0,0 +1 @@
+# Chapter 72

tests/gui/books/sidebar-scroll/src/chapter_73.md

@@ -0,0 +1 @@
+# Chapter 73

tests/gui/books/sidebar-scroll/src/chapter_74.md

@@ -0,0 +1 @@
+# Chapter 74

tests/gui/books/sidebar-scroll/src/chapter_75.md

@@ -0,0 +1 @@
+# Chapter 75

tests/gui/books/sidebar-scroll/src/chapter_76.md

@@ -0,0 +1 @@
+# Chapter 76

tests/gui/books/sidebar-scroll/src/chapter_77.md

@@ -0,0 +1 @@
+# Chapter 77

tests/gui/books/sidebar-scroll/src/chapter_78.md

@@ -0,0 +1 @@
+# Chapter 78

tests/gui/books/sidebar-scroll/src/chapter_79.md

@@ -0,0 +1 @@
+# Chapter 79

tests/gui/books/sidebar-scroll/src/chapter_8.md

@@ -0,0 +1 @@
+# Chapter 8

tests/gui/books/sidebar-scroll/src/chapter_80.md

@@ -0,0 +1 @@
+# Chapter 80

tests/gui/books/sidebar-scroll/src/chapter_81.md

@@ -0,0 +1 @@
+# Chapter 81

tests/gui/books/sidebar-scroll/src/chapter_82.md

@@ -0,0 +1 @@
+# Chapter 82

tests/gui/books/sidebar-scroll/src/chapter_83.md

@@ -0,0 +1 @@
+# Chapter 83

tests/gui/books/sidebar-scroll/src/chapter_84.md

@@ -0,0 +1 @@
+# Chapter 84

tests/gui/books/sidebar-scroll/src/chapter_85.md

@@ -0,0 +1 @@
+# Chapter 85

tests/gui/books/sidebar-scroll/src/chapter_86.md

@@ -0,0 +1 @@
+# Chapter 86

tests/gui/books/sidebar-scroll/src/chapter_87.md

@@ -0,0 +1 @@
+# Chapter 87

tests/gui/books/sidebar-scroll/src/chapter_88.md

@@ -0,0 +1 @@
+# Chapter 88

tests/gui/books/sidebar-scroll/src/chapter_89.md

@@ -0,0 +1 @@
+# Chapter 89

tests/gui/books/sidebar-scroll/src/chapter_9.md

@@ -0,0 +1 @@
+# Chapter 9

tests/gui/books/sidebar-scroll/src/chapter_90.md

@@ -0,0 +1 @@
+# Chapter 90

tests/gui/books/sidebar-scroll/src/chapter_91.md

@@ -0,0 +1 @@
+# Chapter 91

tests/gui/books/sidebar-scroll/src/chapter_92.md

@@ -0,0 +1 @@
+# Chapter 92

tests/gui/books/sidebar-scroll/src/chapter_93.md

@@ -0,0 +1 @@
+# Chapter 93

tests/gui/books/sidebar-scroll/src/chapter_94.md

@@ -0,0 +1 @@
+# Chapter 94

tests/gui/books/sidebar-scroll/src/chapter_95.md

@@ -0,0 +1 @@
+# Chapter 95

tests/gui/books/sidebar-scroll/src/chapter_96.md

@@ -0,0 +1 @@
+# Chapter 96