Auto merge of #134907 - Kobzol:rustc-dev-guide-josh, r=ehuss

Turn rustc-dev-guide into a Josh subtree

Discussed on [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/196385-t-compiler.2Fwg-rustc-dev-guide/topic/a.20move.20to.20main.20repo.20.28rust-lang.2Frust.29).

Accompanying rustc-dev-guide PR: https://github.com/rust-lang/rustc-dev-guide/pull/2183

I didn't create a bootstrap step for rustc-dev-guide yet, because the rustc-dev-guide version that we currently use in this repo doesn't have linkcheck enabled and that fails tests.

The subtree starts with commit [ad93c5f1c49f2aeb45f7a4954017b1e607df9f5e](https://github.com/rust-lang/rustc-dev-guide/commit/ad93c5f1c49f2aeb45f7a4954017b1e607df9f5e).

What I did:
```
export DIR=src/doc/rustc-dev-guide

# Remove submodule
git submodule status ${DIR}
git submodule deinit ${DIR}
git rm -r --cached ${DIR}
rm -rf ${DIR}
# Remove rustc-dev-guide from .gitmodules
git commit -m"Removed `${DIR}` submodule"

# Import history with josh
git fetch https://github.com/rust-lang/rustc-dev-guide ad93c5f1c49f2aeb45f7a4954017b1e607df9f5e
josh-filter ':prefix=src/doc/rustc-dev-guide' FETCH_HEAD
git merge --allow-unrelated FILTERED_HEAD

# A few follow-up cleanup commits
```

r? ehuss

1 files changed, 98 insertions, 0 deletions

diff --git a/src/doc/rustc-dev-guide/examples/rustc-interface-getting-diagnostics.rs b/src/doc/rustc-dev-guide/examples/rustc-interface-getting-diagnostics.rs
new file mode 100644
index 00000000000..be37dd867b2
--- /dev/null
+++ b/src/doc/rustc-dev-guide/examples/rustc-interface-getting-diagnostics.rs
@@ -0,0 +1,98 @@
+#![feature(rustc_private)]
+
+extern crate rustc_data_structures;
+extern crate rustc_driver;
+extern crate rustc_error_codes;
+extern crate rustc_errors;
+extern crate rustc_hash;
+extern crate rustc_hir;
+extern crate rustc_interface;
+extern crate rustc_session;
+extern crate rustc_span;
+
+use rustc_errors::emitter::Emitter;
+use rustc_errors::registry::{self, Registry};
+use rustc_errors::translation::Translate;
+use rustc_errors::{DiagCtxt, DiagInner, FluentBundle};
+use rustc_session::config;
+use rustc_span::source_map::SourceMap;
+
+use std::sync::{Arc, Mutex};
+
+struct DebugEmitter {
+    source_map: Arc<SourceMap>,
+    diagnostics: Arc<Mutex<Vec<DiagInner>>>,
+}
+
+impl Translate for DebugEmitter {
+    fn fluent_bundle(&self) -> Option<&FluentBundle> {
+        None
+    }
+
+    fn fallback_fluent_bundle(&self) -> &FluentBundle {
+        panic!("this emitter should not translate message")
+    }
+}
+
+impl Emitter for DebugEmitter {
+    fn emit_diagnostic(&mut self, diag: DiagInner, _: &Registry) {
+        self.diagnostics.lock().unwrap().push(diag);
+    }
+
+    fn source_map(&self) -> Option<&SourceMap> {
+        Some(&self.source_map)
+    }
+}
+
+fn main() {
+    let buffer: Arc<Mutex<Vec<DiagInner>>> = Arc::default();
+    let diagnostics = buffer.clone();
+    let config = rustc_interface::Config {
+        opts: config::Options::default(),
+        // This program contains a type error.
+        input: config::Input::Str {
+            name: rustc_span::FileName::Custom("main.rs".into()),
+            input: "
+fn main() {
+    let x: &str = 1;
+}
+"
+            .into(),
+        },
+        crate_cfg: Vec::new(),
+        crate_check_cfg: Vec::new(),
+        output_dir: None,
+        output_file: None,
+        file_loader: None,
+        locale_resources: rustc_driver::DEFAULT_LOCALE_RESOURCES.to_owned(),
+        lint_caps: rustc_hash::FxHashMap::default(),
+        psess_created: Some(Box::new(|parse_sess| {
+            parse_sess.set_dcx(DiagCtxt::new(Box::new(DebugEmitter {
+                source_map: parse_sess.clone_source_map(),
+                diagnostics,
+            })));
+        })),
+        register_lints: None,
+        override_queries: None,
+        registry: registry::Registry::new(rustc_errors::codes::DIAGNOSTICS),
+        make_codegen_backend: None,
+        expanded_args: Vec::new(),
+        ice_file: None,
+        hash_untracked_state: None,
+        using_internal_features: Arc::default(),
+    };
+    rustc_interface::run_compiler(config, |compiler| {
+        let krate = rustc_interface::passes::parse(&compiler.sess);
+        rustc_interface::create_and_enter_global_ctxt(&compiler, krate, |tcx| {
+            // Run the analysis phase on the local crate to trigger the type error.
+            let _ = tcx.analysis(());
+        });
+        // If the compiler has encountered errors when this closure returns, it will abort (!) the program.
+        // We avoid this by resetting the error count before returning
+        compiler.sess.dcx().reset_err_count();
+    });
+    // Read buffered diagnostics.
+    buffer.lock().unwrap().iter().for_each(|diagnostic| {
+        println!("{diagnostic:#?}");
+    });
+}