Rustc pull

Author: BoxyUwU

Diff for: .github/workflows/ci.yml

@@ -109,7 +109,7 @@ jobs:
       # intensive jobs to run on free runners, which however also have
       # less disk space.
       - name: free up disk space
-        uses: jlumbroso/free-disk-space@54081f138730dfa15788a46383842cd2f914a1be
+        run: src/ci/scripts/free-disk-space.sh
         if: matrix.free_disk
 
       # Rust Log Analyzer can't currently detect the PR number of a GitHub

Diff for: .gitignore

@@ -83,6 +83,7 @@ __pycache__/
 node_modules
 package-lock.json
 package.json
+/src/doc/rustc-dev-guide/mermaid.min.js
 
 ## Rustdoc GUI tests
 tests/rustdoc-gui/src/**.lock

Diff for: CONTRIBUTING.md

@@ -12,6 +12,15 @@ Documentation for contributing to the compiler or tooling is located in the [Gui
 Development][rustc-dev-guide], commonly known as the [rustc-dev-guide]. Documentation for the
 standard library in the [Standard library developers Guide][std-dev-guide], commonly known as the [std-dev-guide].
 
+## Making changes to subtrees and submodules
+
+For submodules, changes need to be made against the repository corresponding the
+submodule, and not the main `rust-lang/rust` repository.
+
+For subtrees, prefer sending a PR against the subtree's repository if it does
+not need to be made against the main `rust-lang/rust` repostory (e.g. a
+rustc-dev-guide change that does not accompany a compiler change).
+
 ## About the [rustc-dev-guide]
 
 The [rustc-dev-guide] is meant to help document how rustc –the Rust compiler– works,