Rename DiagnosticBuilder as Diag.

Much better!

Note that this involves renaming (and updating the value of)
`DIAGNOSTIC_BUILDER` in clippy.

compiler/rustc_query_system/src/query/job.rs

@@ -4,7 +4,7 @@ use crate::query::plumbing::CycleError;
 use crate::query::DepKind;
 use crate::query::{QueryContext, QueryStackFrame};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::{DiagCtxt, DiagnosticBuilder};
+use rustc_errors::{Diag, DiagCtxt};
 use rustc_hir::def::DefKind;
 use rustc_session::Session;
 use rustc_span::Span;
@@ -559,7 +559,7 @@ pub fn deadlock(query_map: QueryMap, registry: &rayon_core::Registry) {
 pub fn report_cycle<'a>(
     sess: &'a Session,
     CycleError { usage, cycle: stack }: &CycleError,
-) -> DiagnosticBuilder<'a> {
+) -> Diag<'a> {
     assert!(!stack.is_empty());
 
     let span = stack[0].query.default_span(stack[1 % stack.len()].span);

compiler/rustc_query_system/src/query/plumbing.rs

@@ -19,7 +19,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lock;
 #[cfg(parallel_compiler)]
 use rustc_data_structures::{outline, sync};
-use rustc_errors::{DiagnosticBuilder, FatalError, StashKey};
+use rustc_errors::{Diag, FatalError, StashKey};
 use rustc_span::{Span, DUMMY_SP};
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
@@ -124,7 +124,7 @@ fn handle_cycle_error<Q, Qcx>(
     query: Q,
     qcx: Qcx,
     cycle_error: &CycleError,
-    error: DiagnosticBuilder<'_>,
+    error: Diag<'_>,
 ) -> Q::Value
 where
     Q: QueryConfig<Qcx>,