Slightly clean up some lint infra code

* inline `LintBuffer::add_lint`, it only had a single use
* update a lint infra example code snippet
* it used the wrong API (the snippet isn't tested)
* presumably the arguments were updated from builder to diag struct style
at some point without updating the method

Author: fmease

compiler/rustc_lint_defs/src/lib.rs

@@ -764,19 +764,7 @@ pub struct LintBuffer {
 
 implLintBuffer{
 pubfnadd_early_lint(&mutself,early_lint:BufferedEarlyLint){
-let arr = self.map.entry(early_lint.node_id).or_default();
- arr.push(early_lint);
-}
-
-pubfnadd_lint(
-&mutself,
-lint:&'staticLint,
-node_id:NodeId,
-span:MultiSpan,
-diagnostic:BuiltinLintDiag,
-){
-let lint_id = LintId::of(lint);
-self.add_early_lint(BufferedEarlyLint{ lint_id, node_id, span, diagnostic });
+self.map.entry(early_lint.node_id).or_default().push(early_lint);
 }
 
 pubfntake(&mutself,id:NodeId) -> Vec<BufferedEarlyLint>{
@@ -787,11 +775,16 @@ impl LintBuffer {
 pubfnbuffer_lint(
 &mutself,
 lint:&'staticLint,
-id:NodeId,
-sp:implInto<MultiSpan>,
+node_id:NodeId,
+span:implInto<MultiSpan>,
 diagnostic:BuiltinLintDiag,
 ){
-self.add_lint(lint, id, sp.into(), diagnostic)
+self.add_early_lint(BufferedEarlyLint{
+lint_id:LintId::of(lint),
+ node_id,
+span: span.into(),
+ diagnostic,
+});
 }
 }
 

compiler/rustc_macros/src/diagnostics/mod.rs

@@ -91,7 +91,7 @@ pub fn diagnostic_derive(mut s: Structure<'_>) -> TokenStream {
 /// Then, later, to emit the error:
 ///
 /// ```ignore (rust)
-/// cx.span_lint(INVALID_ATOMIC_ORDERING, fail_order_arg_span, AtomicOrderingInvalidLint {
+/// cx.emit_span_lint(INVALID_ATOMIC_ORDERING, fail_order_arg_span, AtomicOrderingInvalidLint {
 /// method,
 /// success_ordering,
 /// fail_ordering,