Rollup merge of #87288 - ijackson:rustdoc-theme, r=GuillaumeGomez

rustdoc: Restore --default-theme, etc, by restoring varname escaping

In #86157

    cd0f93193c
    Use Tera templates for rustdoc.

dropped the following transformation from the keys of the default settings element's `data-` attribute names:

    .map(|(k, v)| format!(r#" data-{}="{}""#, k.replace('-', "_"), Escape(v)))

The `Escape` part is indeed no longer needed, because Tera does that for us.  But the massaging of `-` to `_` is needed, for the (bizarre) reasons explained in the new comments.

I have tested that the default theme function works again for me.  I have also verified that passing (in shell syntax)

    '--default-theme="zork&"'

escapes the value in the HTML.

Closes #87263

src/test/rustdoc-gui/default-settings.goml

@@ -0,0 +1,8 @@
+// This test ensures that the default settings are correctly applied.
+//
+// The "settings" crate uses "ayu" as default setting, which is what we will
+// check.
+goto: file://|DOC_PATH|/settings/index.html
+// Wait a bit to be sure the default theme is applied.
+wait-for: 1000
+assert-css: ("body", {"background-color": "rgb(15, 20, 25)"})

src/test/rustdoc-gui/src/Cargo.toml

@@ -1,6 +0,0 @@
-[workspace]
-members = [
-    "test_docs",
-    "lib2",
-    "implementors",
-]

src/test/rustdoc-gui/src/lib2/Cargo.lock

@@ -12,7 +12,3 @@ version = "0.1.0"
 dependencies = [
  "implementors",
 ]
-
-[[package]]
-name = "test_docs"
-version = "0.1.0"

src/test/rustdoc-gui/src/lib2/Cargo.toml

@@ -7,4 +7,4 @@ edition = "2018"
 path = "lib.rs"
 
 [dependencies]
-implementors = { path = "../implementors" }
+implementors = { path = "./implementors" }

src/test/rustdoc-gui/src/lib2/implementors/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "implementors"
+version = "0.1.0"

src/test/rustdoc-gui/src/settings/.cargo/config.toml

@@ -0,0 +1,2 @@
+[build]
+rustdocflags = ["--default-theme", "ayu"]

src/test/rustdoc-gui/src/settings/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "settings"
+version = "0.1.0"

src/test/rustdoc-gui/src/settings/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "settings"
+version = "0.1.0"
+edition = "2018"
+
+[lib]
+path = "lib.rs"

src/test/rustdoc-gui/src/settings/lib.rs

@@ -0,0 +1 @@
+pub fn foo() {}

src/test/rustdoc-gui/src/test_docs/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "test_docs"
+version = "0.1.0"