Update E0038 to the new error format

[munyari]

Part of #35233

Addresses #35500
"r? @jonathandturner

This doesn't compile yet, and I need help. In my naive solution, adding the span label makes our error message a mutable errors::DiagnosticBuilder pointer.

python src/bootstrap/bootstrap.py --step check-cfail E0038 --stage 1

Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   Compiling rustc v0.0.0 (file:///home/nash/code/rust/src/librustc)
src/librustc/traits/error_reporting.rs:735:9: 735:12 error: mismatched types [E0308]
src/librustc/traits/error_reporting.rs:735         err
                                                   ^~~
src/librustc/traits/error_reporting.rs:735:9: 735:12 help: run `rustc --explain E0308` to see a detailed explanation
src/librustc/traits/error_reporting.rs:735:9: 735:12 note: expected type `core::option::Option<errors::DiagnosticBuilder<'tcx>>`
src/librustc/traits/error_reporting.rs:735:9: 735:12 note:    found type `core::option::Option<&mut errors::DiagnosticBuilder<'_>>`
error: aborting due to previous error
error: Could not compile `rustc`.

To learn more, run the command again with --verbose.


command did not execute successfully: "/home/nash/code/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "-j" "4" "--target" "x86_64-unknown-linux-gnu" "--release" "--features" " jemalloc" "--manifest-path" "/home/nash/code/rust/src/rustc/Cargo.toml"
expected success, got: exit code: 101

[sophiajt]

@munyari - .span_label(..) takes in a &mut and returns &mut. It's used for chaining calls together. You don't have to use it that way. Instead, you can create a temporary to hold the value from struct_span_err! and call .span_label() on the temporary without using that in the Some.

Something like this:

        let mut err = match warning_node_id {
            Some(_) => None,
            None => {
                let trait_str = self.item_path_str(trait_def_id);
                let mut db = struct_span_err!(
                            self.sess, span, E0038,
                            "the trait `{}` cannot be made into an object",
                            trait_str);
                db.span_label(span,
                            &format!("the trait `{}` cannot be made \
                            into an object", trait_str));
                Some(db)
            }
        };

[sophiajt]

Also, when you update this label, be sure to run:

python src/bootstrap/bootstrap.py --stage 1 --step check-cfail

I'm seeing 6 unit tests that will also need to be updated once you add the label.

[munyari]

@jonathandturner I just made the update

[sophiajt]

Looks good!

@bors r+ rollup

[bors]

📌 Commit 20ea8cb has been approved by jonathandturner