Rollup merge of #139562 - notriddle:notriddle/ew-resize, r=GuillaumeGomez

rustdoc: add a handle that makes sidebar resizing more obvious

This aims to make the resizable sidebars more obvious

Preview: <https://notriddle.com/rustdoc-html-demo-12/sidebar-resize-handle/std/index.html>

![image](https://github.com/user-attachments/assets/d4d70982-8045-4fed-818a-982108b0d3b3)

![image](https://github.com/user-attachments/assets/4aaa3663-19f3-4e04-89c6-53db0ddb72ed)

![image](https://github.com/user-attachments/assets/3f612c5b-6be1-4383-801a-067c87425eb9)

This change is based on some discussion on [lolbinarycat's idea], but with a more "traditional" design. Specifically, while very few systems use exactly this design, most of them use [a skeumorph](https://ux.stackexchange.com/questions/80463/what-do-the-3-close-horizontal-bars-not-hamburger-menu-represent-and-what-is-t/80591#80591) of a grip texture:

- This design is similar to the one used in the Rust Playground, and almost identical to UX StackExchange:

  <details><img src="https://github.com/user-attachments/assets/39a6bb69-4895-4fd0-87da-b87913bc7309"></details>

  <details><img src="https://github.com/user-attachments/assets/a41942e1-651b-410b-b855-2aafe8fe54f4"></details>

- In Jira, resizable sidebars have a stack of four dots, but only in one row.

  <details><img src="https://github.com/user-attachments/assets/13047998-02bf-47e6-b796-16f393f870b0"></details>

- In The GIMP, resizable sidebars have a stack of three dots.

  <details><img src="https://github.com/user-attachments/assets/138f5c21-3069-4bbe-b306-0bb9a4bf0318"></details>

- In [old Windows], "panes" are defined to have the same border style as a window, which has a raised appearance. To evoke this, the PR adds a lightweight "shadow" border, darker than the sidebar itself

  <details><img src="https://github.com/user-attachments/assets/301da4b8-6c48-4131-b741-1689af84670a"></details>

- In [NeXT], a drag point usually had an innie, whether the line in a slider or the circle in a scroller; I can also hide and show the favorites bar in Workspace by dragging on a circular "grip spot"

  <details><img src="https://github.com/user-attachments/assets/b13c2d30-a3a8-4672-90fa-58c1fdf19f42"></details>

- In [old Mac], drag handles for things usually had a "grip track" of parallel lines.

  <details><img src="https://github.com/user-attachments/assets/1fbecc67-ffbc-4ed6-a8c5-a9ff085638db"></details>

  *This design is far closer to old Mac than anything else*, though they've put it in the bottom corner instead of the middle.

- [OSX] kept that, but the "Source List" part of the Finder still had the circle grip for a time the same way Workspace did (resulting in an odd mishmash, if you compare the source list sidebar with the other grip tracks embedded in the scrollbars).

  <details><img src="https://github.com/user-attachments/assets/551b8f9d-2dd8-4291-917f-dc88741a2b97"></details>

[lolbinarycat's idea]: https://github.com/rust-lang/rust/pull/139420
[old Windows]: https://archive.org/details/windowsinterface00micr/page/n9/mode/2up
[old Mac]: https://archive.org/details/apple-hig/1996_Human_Interface_Guidelines_for_Mac_OS_8_%28WWDC_Release%29/page/16/mode/2up
[NeXT]: https://archive.org/details/apple-hig/1993%20NeXTSTEP%20User%20Interface%20Guidelines%20-%20Release%203/page/145/mode/2up
[OSX]: https://dn721903.ca.archive.org/0/items/apple-hig/MacOSX_HIG_2005_09_08.pdf#page=267

3 files changed, 41 insertions, 15 deletions

diff --git a/src/librustdoc/html/static/css/noscript.css b/src/librustdoc/html/static/css/noscript.css
index 477a79d63e9..a3c6bf98161 100644
--- a/src/librustdoc/html/static/css/noscript.css
+++ b/src/librustdoc/html/static/css/noscript.css
@@ -43,6 +43,7 @@ nav.sub {
 	--settings-button-border-focus: #717171;
 	--sidebar-background-color: #f5f5f5;
 	--sidebar-background-color-hover: #e0e0e0;
+	--sidebar-border-color: #ddd;
 	--code-block-background-color: #f5f5f5;
 	--scrollbar-track-background-color: #dcdcdc;
 	--scrollbar-thumb-background-color: rgba(36, 37, 39, 0.6);
@@ -149,6 +150,7 @@ nav.sub {
 		--settings-button-border-focus: #ffb900;
 		--sidebar-background-color: #505050;
 		--sidebar-background-color-hover: #676767;
+		--sidebar-border-color: #2A2A2A;
 		--code-block-background-color: #2A2A2A;
 		--scrollbar-track-background-color: #717171;
 		--scrollbar-thumb-background-color: rgba(32, 34, 37, .6);
diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index f838f3f1106..a81d5c9c49b 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -1,4 +1,6 @@
-/* When static files are updated, their suffixes need to be updated.
+/* ignore-tidy-filelength */
+/*
+	When static files are updated, their suffixes need to be updated.
 	1. In the top directory run:
 		./x.py doc --stage 1 library/core
 	2. Find the directory containing files named with updated suffixes:
@@ -496,12 +498,13 @@ img {
 	top: 0;
 	left: 0;
 	z-index: var(--desktop-sidebar-z-index);
+	/* resize indicator: hide this when on touch or mobile */
+	border-right: solid 1px var(--sidebar-border-color);
 }
 
 .rustdoc.src .sidebar {
 	flex-basis: 50px;
 	width: 50px;
-	border-right: 1px solid;
 	overflow-x: hidden;
 	/* The sidebar is by default hidden  */
 	overflow-y: hidden;
@@ -515,12 +518,27 @@ img {
 .sidebar-resizer {
 	touch-action: none;
 	width: 9px;
-	cursor: col-resize;
+	cursor: ew-resize;
 	z-index: calc(var(--desktop-sidebar-z-index) + 1);
 	position: fixed;
 	height: 100%;
-	/* make sure there's a 1px gap between the scrollbar and resize handle */
-	left: calc(var(--desktop-sidebar-width) + 1px);
+	left: var(--desktop-sidebar-width);
+	display: flex;
+	align-items: center;
+	justify-content: flex-start;
+	color: var(--right-side-color);
+}
+.sidebar-resizer::before {
+	content: "";
+	border-right: dotted 2px currentColor;
+	width: 2px;
+	height: 12px;
+}
+.sidebar-resizer::after {
+	content: "";
+	border-right: dotted 2px currentColor;
+	width: 2px;
+	height: 16px;
 }
 
 .rustdoc.src .sidebar-resizer {
@@ -543,11 +561,12 @@ img {
 }
 
 .sidebar-resizing * {
-	cursor: col-resize !important;
+	cursor: ew-resize !important;
 }
 
 .sidebar-resizing .sidebar {
 	position: fixed;
+	border-right: solid 2px var(--sidebar-resizer-active);
 }
 .sidebar-resizing > body {
 	padding-left: var(--resizing-sidebar-width);
@@ -561,8 +580,9 @@ img {
 	margin: 0;
 	/* when active or hovered, place resizer glow on top of the sidebar (right next to, or even
 	   on top of, the scrollbar) */
-	left: var(--desktop-sidebar-width);
+	left: calc(var(--desktop-sidebar-width) - 1px);
 	border-left: solid 1px var(--sidebar-resizer-hover);
+	color: var(--sidebar-resizer-hover);
 }
 
 .src-sidebar-expanded .rustdoc.src .sidebar-resizer:hover,
@@ -578,21 +598,20 @@ img {
 		/* too easy to hit the resizer while trying to hit the [-] toggle */
 		display: none !important;
 	}
+	.sidebar {
+		/* resize indicator: hide this when on touch or mobile */
+		border-right: none;
+	}
 }
 
 .sidebar-resizer.active {
 	/* make the resize tool bigger when actually resizing, to avoid :hover styles on other stuff
 		while resizing */
 	padding: 0 140px;
-	width: 2px;
+	width: calc(140px + 140px + 9px + 2px);
 	margin-left: -140px;
 	border-left: none;
-}
-.sidebar-resizer.active::before {
-	border-left: solid 2px var(--sidebar-resizer-active);
-	display: block;
-	height: 100%;
-	content: "";
+	color: var(--sidebar-resizer-active);
 }
 
 .sidebar, .mobile-topbar, .sidebar-menu-toggle,
@@ -2509,6 +2528,8 @@ in src-script.js and main.js
 		/* Reduce height slightly to account for mobile topbar. */
 		height: calc(100vh - 45px);
 		width: 200px;
+		/* resize indicator: hide this when on touch or mobile */
+		border-right: none;
 	}
 
 	/* The source view uses a different design for the sidebar toggle, and doesn't have a topbar,
@@ -2897,6 +2918,7 @@ by default.
 	--settings-button-border-focus: #717171;
 	--sidebar-background-color: #f5f5f5;
 	--sidebar-background-color-hover: #e0e0e0;
+	--sidebar-border-color: #ddd;
 	--code-block-background-color: #f5f5f5;
 	--scrollbar-track-background-color: #dcdcdc;
 	--scrollbar-thumb-background-color: rgba(36, 37, 39, 0.6);
@@ -3002,6 +3024,7 @@ by default.
 	--settings-button-border-focus: #ffb900;
 	--sidebar-background-color: #505050;
 	--sidebar-background-color-hover: #676767;
+	--sidebar-border-color: #999;
 	--code-block-background-color: #2A2A2A;
 	--scrollbar-track-background-color: #717171;
 	--scrollbar-thumb-background-color: rgba(32, 34, 37, .6);
@@ -3114,6 +3137,7 @@ Original by Dempfi (https://github.com/dempfi/ayu)
 	--settings-button-border-focus: #e0e0e0;
 	--sidebar-background-color: #14191f;
 	--sidebar-background-color-hover: rgba(70, 70, 70, 0.33);
+	--sidebar-border-color: #5c6773;
 	--code-block-background-color: #191f26;
 	--scrollbar-track-background-color: transparent;
 	--scrollbar-thumb-background-color: #5c6773;
diff --git a/src/librustdoc/html/templates/page.html b/src/librustdoc/html/templates/page.html
index 5ef376f4acb..7af99e7097c 100644
--- a/src/librustdoc/html/templates/page.html
+++ b/src/librustdoc/html/templates/page.html
@@ -114,7 +114,7 @@
         {% endif %}
         {{ sidebar|safe }}
     </nav> {# #}
-    <div class="sidebar-resizer"></div> {# #}
+    <div class="sidebar-resizer" title="Drag to resize sidebar"></div> {# #}
     <main>
         {% if page.css_class != "src" %}<div class="width-limiter">{% endif %}
             {# defined in storage.js to avoid duplicating complex UI across every page #}