text emitter: suggest adding //@check-pass when no error patterns present

CHANGELOG.md

@@ -5,6 +5,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+### Fixed
+
+### Changed
+
+- when a test file has no error patterns, there's now a suggestion to add `//@check-pass`
+
 ## [0.30.4] - 2025-11-24
 
 ### Added

src/status_emitter/text.rs

@@ -657,7 +657,7 @@ fn print_error(error: &Error, path: &Path) {
                     format!("`{s}` not found in diagnostics {line}")
                 }
                 Pattern::Regex(r) => {
-                    format!("`/{r}/` does not match diagnostics {line}",)
+                    format!("`/{r}/` does not match diagnostics {line}")
                 }
             };
             // This will print a suitable error header.
@@ -671,9 +671,9 @@ fn print_error(error: &Error, path: &Path) {
             code,
             expected_line,
         } => {
-            let line = match expected_line {
-                Some(line) => format!("on line {line}"),
-                None => format!("outside the testfile"),
+            let line: Cow<_> = match expected_line {
+                Some(line) => format!("on line {line}").into(),
+                None => "outside the testfile".into(),
             };
             create_error(
                 format!("diagnostic code `{}` not found {line}", &**code),
@@ -683,6 +683,7 @@ fn print_error(error: &Error, path: &Path) {
         }
         Error::NoPatternsFound => {
             print_error_header("expected error patterns, but found none");
+            println!("If this is expected, consider annotating the file with `//@check-pass`");
         }
         Error::PatternFoundInPassTest { mode, span } => {
             let annot = [("expected because of this annotation", span.clone())];

tests/integrations/basic-fail/Cargo.stdout

@@ -333,6 +333,7 @@
  = note: compilation succeeded, but was expected to fail
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 
@@ -855,9 +856,9 @@
 tests/actual_tests_bless/revisions.rs (revision `bar`) ... ok
 tests/actual_tests_bless/revisions_bad.rs ... ok
 tests/actual_tests_bless/revisions_bad.rs (revision `foo`) ... ok
 tests/actual_tests_bless/revisions_bad.rs (revision `bar`) ... FAILED
 tests/actual_tests_bless/revisions_filter.rs ... ok
 tests/actual_tests_bless/revisions_filter.rs (revision `foo`) ... ignored (in-test comment)
 tests/actual_tests_bless/revisions_filter.rs (revision `bar`) ... ignored (in-test comment)
 tests/actual_tests_bless/revisions_filter2.rs ... ok
 tests/actual_tests_bless/revisions_filter2.rs (revision `foo`) ... ignored (in-test comment)
@@ -930,6 +931,7 @@
   |
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 error: expected one of `!` or `::`, found `<eof>`
@@ -1033,6 +1035,7 @@
  = note: compilation succeeded, but was expected to fail
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 
@@ -1054,6 +1057,7 @@
   |
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 error: cannot mix `bin` crate type with others
@@ -1079,6 +1083,7 @@
  = note: compilation succeeded, but was expected to fail
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 
@@ -1321,6 +1326,7 @@
  = note: compilation succeeded, but was expected to fail
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 full stderr:
 warning: unused variable: `Ě电脑`
@@ -1728,6 +1734,7 @@
  = note: compilation succeeded, but was expected to fail
 
 error: expected error patterns, but found none
+If this is expected, consider annotating the file with `//@check-pass`
 
 
 FAILED TEST: tests/actual_tests/filters.rs