add OR_PATTERNS_BACK_COMPAT lint

test: add more cases

test: add comments

refine msg

compiler/rustc_lint/src/context.rs

@@ -709,6 +709,9 @@ pub trait LintContext: Sized {
                 BuiltinLintDiagnostics::ProcMacroBackCompat(note) => {
                     db.note(&note);
                 }
+                BuiltinLintDiagnostics::OrPatternsBackCompat(span,suggestion) => {
+                    db.span_suggestion(span, "use pat2015 to preserve semantics", suggestion, Applicability::MachineApplicable);
+                }
             }
             // Rewrap `db`, and pass control to the user.
             decorate(LintDiagnosticBuilder::new(db));