Auto merge of rust-lang#101986 - WaffleLapkin:move_lint_note_to_the_bottom, r=estebank

Move lint level source explanation to the bottom

So, uhhhhh

r? `@estebank`

## User-facing change

"note: `#[warn(...)]` on by default" and such are moved to the bottom of the diagnostic:
```diff
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue rust-lang#87678 <rust-lang#87678>
+   = note: `#[warn(unsupported_calling_conventions)]` on by default
```

Why warning is enabled is the least important thing, so it shouldn't be the first note the user reads, IMO.

## Developer-facing change

`struct_span_lint` and similar methods have a different signature.

Before: `..., impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>)`
After: `..., impl Into<DiagnosticMessage>, impl for<'a, 'b> FnOnce(&'b mut DiagnosticBuilder<'a, ()>) -> &'b mut DiagnosticBuilder<'a, ()>`

The reason for this is that `struct_span_lint` needs to edit the diagnostic _after_ `decorate` closure is called. This also makes lint code a little bit nicer in my opinion.

Another option is to use `impl for<'a> FnOnce(LintDiagnosticBuilder<'a, ()>) -> DiagnosticBuilder<'a, ()>` altough I don't _really_ see reasons to do `let lint = lint.build(message)` everywhere.

## Subtle problem

By moving the message outside of the closure (that may not be called if the lint is disabled) `format!(...)` is executed earlier, possibly formatting `Ty` which may call a query that trims paths that crashes the compiler if there were no warnings...

I don't think it's that big of a deal, considering that we move from `format!(...)` to `fluent` (which is lazy by-default) anyway, however this required adding a workaround which is unfortunate.

## P.S.

I'm sorry, I do not how to make this PR smaller/easier to review. Changes to the lint API affect SO MUCH 😢

Author: bors

clippy_lints/src/module_style.rs

@@ -117,11 +117,13 @@ impl EarlyLintPass for ModStyle {
                     cx.struct_span_lint(
                         SELF_NAMED_MODULE_FILES,
                         Span::new(file.start_pos, file.start_pos, SyntaxContext::root(), None),
-                        |build| {
-                            let mut lint =
-                                build.build(&format!("`mod.rs` files are required, found `{}`", path.display()));
-                            lint.help(&format!("move `{}` to `{}`", path.display(), correct.display(),));
-                            lint.emit();
+                        format!("`mod.rs` files are required, found `{}`", path.display()),
+                        |lint| {
+                            lint.help(format!(
+                                "move `{}` to `{}`",
+                                path.display(),
+                                correct.display(),
+                            ))
                         },
                     );
                 }
@@ -156,11 +158,8 @@ fn check_self_named_mod_exists(cx: &EarlyContext<'_>, path: &Path, file: &Source
         cx.struct_span_lint(
             MOD_MODULE_FILES,
             Span::new(file.start_pos, file.start_pos, SyntaxContext::root(), None),
-            |build| {
-                let mut lint = build.build(&format!("`mod.rs` files are not allowed, found `{}`", path.display()));
-                lint.help(&format!("move `{}` to `{}`", path.display(), mod_file.display(),));
-                lint.emit();
-            },
+            format!("`mod.rs` files are not allowed, found `{}`", path.display()),
+            |lint| lint.help(format!("move `{}` to `{}`", path.display(), mod_file.display())),
         );
     }
 }

clippy_utils/src/diagnostics.rs

@@ -47,10 +47,9 @@ fn docs_link(diag: &mut Diagnostic, lint: &'static Lint) {
 ///    |     ^^^^^^^^^^^^^^^^^^^^^^^
 /// ```
 pub fn span_lint<T: LintContext>(cx: &T, lint: &'static Lint, sp: impl Into<MultiSpan>, msg: &str) {
-    cx.struct_span_lint(lint, sp, |diag| {
-        let mut diag = diag.build(msg);
-        docs_link(&mut diag, lint);
-        diag.emit();
+    cx.struct_span_lint(lint, sp, msg, |diag| {
+        docs_link(diag, lint);
+        diag
     });
 }
 
@@ -82,15 +81,14 @@ pub fn span_lint_and_help<'a, T: LintContext>(
     help_span: Option<Span>,
     help: &str,
 ) {
-    cx.struct_span_lint(lint, span, |diag| {
-        let mut diag = diag.build(msg);
+    cx.struct_span_lint(lint, span, msg, |diag| {
         if let Some(help_span) = help_span {
             diag.span_help(help_span, help);
         } else {
             diag.help(help);
         }
-        docs_link(&mut diag, lint);
-        diag.emit();
+        docs_link(diag, lint);
+        diag
     });
 }
 
@@ -125,15 +123,14 @@ pub fn span_lint_and_note<'a, T: LintContext>(
     note_span: Option<Span>,
     note: &str,
 ) {
-    cx.struct_span_lint(lint, span, |diag| {
-        let mut diag = diag.build(msg);
+    cx.struct_span_lint(lint, span, msg, |diag| {
         if let Some(note_span) = note_span {
             diag.span_note(note_span, note);
         } else {
             diag.note(note);
         }
-        docs_link(&mut diag, lint);
-        diag.emit();
+        docs_link(diag, lint);
+        diag
     });
 }
 
@@ -147,19 +144,17 @@ where
     S: Into<MultiSpan>,
     F: FnOnce(&mut Diagnostic),
 {
-    cx.struct_span_lint(lint, sp, |diag| {
-        let mut diag = diag.build(msg);
-        f(&mut diag);
-        docs_link(&mut diag, lint);
-        diag.emit();
+    cx.struct_span_lint(lint, sp, msg, |diag| {
+        f(diag);
+        docs_link(diag, lint);
+        diag
     });
 }
 
 pub fn span_lint_hir(cx: &LateContext<'_>, lint: &'static Lint, hir_id: HirId, sp: Span, msg: &str) {
-    cx.tcx.struct_span_lint_hir(lint, hir_id, sp, |diag| {
-        let mut diag = diag.build(msg);
-        docs_link(&mut diag, lint);
-        diag.emit();
+    cx.tcx.struct_span_lint_hir(lint, hir_id, sp, msg, |diag| {
+        docs_link(diag, lint);
+        diag
     });
 }
 
@@ -171,11 +166,10 @@ pub fn span_lint_hir_and_then(
     msg: &str,
     f: impl FnOnce(&mut Diagnostic),
 ) {
-    cx.tcx.struct_span_lint_hir(lint, hir_id, sp, |diag| {
-        let mut diag = diag.build(msg);
-        f(&mut diag);
-        docs_link(&mut diag, lint);
-        diag.emit();
+    cx.tcx.struct_span_lint_hir(lint, hir_id, sp, msg, |diag| {
+        f(diag);
+        docs_link(diag, lint);
+        diag
     });
 }
 

tests/ui-toml/await_holding_invalid_type/await_holding_invalid_type.stderr

@@ -4,8 +4,8 @@ error: `std::string::String` may not be held across an `await` point per `clippy
 LL |     let _x = String::from("hello");
    |         ^^
    |
-   = note: `-D clippy::await-holding-invalid-type` implied by `-D warnings`
    = note: strings are bad
+   = note: `-D clippy::await-holding-invalid-type` implied by `-D warnings`
 
 error: `std::net::Ipv4Addr` may not be held across an `await` point per `clippy.toml`
   --> $DIR/await_holding_invalid_type.rs:10:9

tests/ui-toml/conf_deprecated_key/conf_deprecated_key.stderr

@@ -8,8 +8,8 @@ error: the function has a cognitive complexity of (3/2)
 LL | fn cognitive_complexity() {
    |    ^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::cognitive-complexity` implied by `-D warnings`
    = help: you could split it up into multiple smaller functions
+   = note: `-D clippy::cognitive-complexity` implied by `-D warnings`
 
 error: aborting due to previous error; 2 warnings emitted
 

tests/ui-toml/expect_used/expect_used.stderr

@@ -4,8 +4,8 @@ error: used `expect()` on `an Option` value
 LL |     let _ = opt.expect("");
    |             ^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::expect-used` implied by `-D warnings`
    = help: if this value is `None`, it will panic
+   = note: `-D clippy::expect-used` implied by `-D warnings`
 
 error: used `expect()` on `a Result` value
   --> $DIR/expect_used.rs:11:13

tests/ui-toml/fn_params_excessive_bools/test.stderr

@@ -4,8 +4,8 @@ error: more than 1 bools in function parameters
 LL | fn g(_: bool, _: bool) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::fn-params-excessive-bools` implied by `-D warnings`
    = help: consider refactoring bools into two-variant enums
+   = note: `-D clippy::fn-params-excessive-bools` implied by `-D warnings`
 
 error: aborting due to previous error
 

tests/ui-toml/large_include_file/large_include_file.stderr

@@ -4,8 +4,8 @@ error: attempted to include a large file
 LL | const TOO_BIG_INCLUDE_BYTES: &[u8; 654] = include_bytes!("too_big.txt");
    |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::large-include-file` implied by `-D warnings`
    = note: the configuration allows a maximum size of 600 bytes
+   = note: `-D clippy::large-include-file` implied by `-D warnings`
    = note: this error originates in the macro `include_bytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: attempted to include a large file

tests/ui-toml/nonstandard_macro_braces/conf_nonstandard_macro_braces.stderr

@@ -4,12 +4,12 @@ error: use of irregular braces for `vec!` macro
 LL |     let _ = vec! {1, 2, 3};
    |             ^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::nonstandard-macro-braces` implied by `-D warnings`
 help: consider writing `vec![1, 2, 3]`
   --> $DIR/conf_nonstandard_macro_braces.rs:43:13
    |
 LL |     let _ = vec! {1, 2, 3};
    |             ^^^^^^^^^^^^^^
+   = note: `-D clippy::nonstandard-macro-braces` implied by `-D warnings`
 
 error: use of irregular braces for `format!` macro
   --> $DIR/conf_nonstandard_macro_braces.rs:44:13

tests/ui-toml/strict_non_send_fields_in_send_ty/test.stderr

@@ -4,13 +4,13 @@ error: some fields in `NoGeneric` are not safe to be sent to another thread
 LL | unsafe impl Send for NoGeneric {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `-D clippy::non-send-fields-in-send-ty` implied by `-D warnings`
 note: it is not safe to send field `rc_is_not_send` to another thread
   --> $DIR/test.rs:8:5
    |
 LL |     rc_is_not_send: Rc<String>,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    = help: use a thread-safe type that implements `Send`
+   = note: `-D clippy::non-send-fields-in-send-ty` implied by `-D warnings`
 
 error: some fields in `MultiField<T>` are not safe to be sent to another thread
   --> $DIR/test.rs:19:1

tests/ui-toml/struct_excessive_bools/test.stderr

@@ -6,8 +6,8 @@ LL | |     a: bool,
 LL | | }
    | |_^
    |
-   = note: `-D clippy::struct-excessive-bools` implied by `-D warnings`
    = help: consider using a state machine or refactoring bools into two-variant enums
+   = note: `-D clippy::struct-excessive-bools` implied by `-D warnings`
 
 error: aborting due to previous error