6abe64871e
Add clearer error message using `&str + &str` This is the first part of #39018. One of the common things for new users coming from more dynamic languages like JavaScript, Python or Ruby is to use `+` to concatenate strings. However, this doesn't work that way in Rust unless the first type is a `String`. This commit adds a check for this use case and outputs a new error as well as a suggestion to guide the user towards the desired behavior. It also adds a new test case to test the output of the error.
Guide to the UI Tests
The UI tests are intended to capture the compiler's complete output,
so that we can test all aspects of the presentation. They work by
compiling a file (e.g., hello_world/main.rs), capturing the output,
and then applying some normalization (see below). This normalized
result is then compared against reference files named
hello_world/main.stderr and hello_world/main.stdout. If either of
those files doesn't exist, the output must be empty. If the test run
fails, we will print out the current output, but it is also saved in
build/<target-triple>/test/ui/hello_world/main.stdout (this path is
printed as part of the test failure mesage), so you can run diff and
so forth.
Editing and updating the reference files
If you have changed the compiler's output intentionally, or you are
making a new test, you can use the script update-references.sh to
update the references. When you run the test framework, it will report
various errors: in those errors is a command you can use to run the
update-references.sh script, which will then copy over the files
from the build directory and use them as the new reference. You can
also just run update-all-references.sh. In both cases, you can run
the script with --help to get a help message.
Normalization
The normalization applied is aimed at filenames:
- the test directory is replaced with
$DIR - all backslashes () are converted to forward slashes (/) (for windows)