dylint_testing

This crate provides convenient access to the compiletest_rs package for testing Dylint libraries.

Specifically, this crate provides the following three functions. Note: If your test has dependencies, you must use ui_test_example or ui_test_examples. See the question_mark_in_expression example in this repository.

• ui_test - test a library on all source files in a directory

  pub fn ui_test(name: &str, src_base: &Path)
  

  • name is the name of a Dylint library to be tested. (Often, this is the same as the package name.)
  • src_base is a directory containing:
    • source files on which to test the library (.rs files), and
    • the output those files should produce (.stderr files).

• ui_test_example - test a library on one example target

  pub fn ui_test_example(name: &str, example: &str)
  

  • name is the name of a Dylint library to be tested.
  • example is an example target on which to test the library.

• ui_test_examples - test a library on all example targets

  pub fn ui_test_examples(name: &str)
  

  • name is the name of a Dylint library to be tested.

For most situations, you can add the following to your library's lib.rs file:

#[test]
fn ui() {
    dylint_testing::ui_test(
        env!("CARGO_PKG_NAME"),
        &std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("ui"),
    );
}

And include one or more .rs and .stderr files in a ui directory alongside your library's src directory. See the examples in this repository.

Test builder

In addition to the above three functions, dylint_testing::ui:Test is a test "builder." Currently, the main advantage of using Test over the above functions is that Test allows flags to be passed to rustc. For an example of its use, see nonreentrant_function_in_test in this repository.

Test has three constructors, which correspond to the above three functions as follows:

• Test::src_base <-> ui_test
• Test::example <-> ui_test_example
• Test::examples <-> ui_test_examples

In each case, the constructor's arguments are exactly those of the corresponding function.

A Test instance has the following methods:

• rustc_flags - pass flags to the compiler when running the test

  pub fn rustc_flags(
      &mut self,
      rustc_flags: impl IntoIterator<Item = impl AsRef<str>>,
  ) -> &mut Self
  

• run - run the test

  pub fn run(&mut self)
  

Updating .stderr files

If the standard error that results from running your .rs file differs from the contents of your .stderr file, compiletest_rs will produce a report like the following:

diff of stderr:

 error: calling `std::env::set_var` in a test could affect the outcome of other tests
   --> $DIR/main.rs:8:5
    |
 LL |     std::env::set_var("KEY", "VALUE");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D nonreentrant-function-in-test` implied by `-D warnings`

-error: aborting due to previous error
+error: calling `std::env::set_var` in a test could affect the outcome of other tests
+  --> $DIR/main.rs:23:9
+   |
+LL |         std::env::set_var("KEY", "VALUE");
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors



The actual stderr differed from the expected stderr.
Actual stderr saved to ...

The meaning of each line is as follows:

• A line beginning with a plus (+) is in the actual standard error, but not in your .stderr file.
• A line beginning with a minus (-) is in your .stderr file, but not in the actual standard error.
• A line beginning with a space ( ) is in both the actual standard error and your .stderr file, and is provided for context.
• All other lines (e.g., diff of stderr:) contain compiletest_rs messages.

Note: In the actual standard error, a blank line usually follows the error: aborting due to N previous errors line. So a correct .stderr file will typically contain one blank line at the end.

In general, it is not too hard to update a .stderr file by hand. However, the compiletest_rs report should contain a line of the form Actual stderr saved to PATH. Copying PATH to your .stderr file should update it completely.

Additional documentation on compiletest_rs can be found in its repository.