Auto merge of #12453 - y21:span_lint_into_diag, r=blyxyas

accept `String` in `span_lint*` functions directly to avoid unnecessary clones

context: https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Accepting.20.60Into.3C.7BSub.7DdiagMessage.3E.60.20in.20.60span_lint*.60.20functions/near/425703273

tldr: the `span_lint*` functions now accept both `String`s, which are then reused and not recloned like before, and also `&'static str`, in which case it [doesn't need to allocate](https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc_error_messages/lib.rs.html#359).
Previously, it accepted `&str` and would always call `.to_string()`, which is worse in any case: it allocates for `&'static str` and forces a clone even if the caller already has a `String`.

---------

This PR has a massive diff, but the only interesting change is in the first commit, which changes the message/help/note parameter in the `span_lint*` functions to not take a `&str`, but an `impl Into<DiagMessage>`.

The second commit changes all of the errors that now occur:
- `&format!(...)` cannot be passed to `span_lint` anymore. Instead, we now simply pass `format!()` directly.
- `Into<DiagMessage>` can be `&'static str`, but not any `&str`. So this requires changing a bunch of other `&str` to `&'static str` at call sites as well.
- Added [`Sugg::into_string`](https://github.com/y21/rust-clippy/blob/9fc88bc2851fbb287d89f65b78fb67af504f8362/clippy_utils/src/sugg.rs#L362), which, as opposed to `Sugg::to_string`, can take advantage of the fact that it takes ownership and is able to reuse the `String`

changelog: none

Author: bors

clippy_lints/src/approx_const.rs

@@ -95,7 +95,7 @@ impl ApproxConstant {
                         cx,
                         APPROX_CONSTANT,
                         e.span,
-                        &format!("approximate value of `{module}::consts::{}` found", &name),
+                        format!("approximate value of `{module}::consts::{}` found", &name),
                         None,
                         "consider using the constant directly",
                     );

clippy_lints/src/asm_syntax.rs

@@ -53,9 +53,9 @@ fn check_asm_syntax(
                 cx,
                 lint,
                 span,
-                &format!("{style} x86 assembly syntax used"),
+                format!("{style} x86 assembly syntax used"),
                 None,
-                &format!("use {} x86 assembly syntax", !style),
+                format!("use {} x86 assembly syntax", !style),
             );
         }
     }

clippy_lints/src/assertions_on_constants.rs

@@ -58,7 +58,7 @@ impl<'tcx> LateLintPass<'tcx> for AssertionsOnConstants {
                 cx,
                 ASSERTIONS_ON_CONSTANTS,
                 macro_call.span,
-                &format!(
+                format!(
                     "`{}!(true)` will be optimized out by the compiler",
                     cx.tcx.item_name(macro_call.def_id)
                 ),
@@ -74,9 +74,9 @@ impl<'tcx> LateLintPass<'tcx> for AssertionsOnConstants {
                 cx,
                 ASSERTIONS_ON_CONSTANTS,
                 macro_call.span,
-                &format!("`assert!(false{assert_arg})` should probably be replaced"),
+                format!("`assert!(false{assert_arg})` should probably be replaced"),
                 None,
-                &format!("use `panic!({panic_arg})` or `unreachable!({panic_arg})`"),
+                format!("use `panic!({panic_arg})` or `unreachable!({panic_arg})`"),
             );
         }
     }

clippy_lints/src/attrs/allow_attributes_without_reason.rs

@@ -30,7 +30,7 @@ pub(super) fn check<'cx>(cx: &LateContext<'cx>, name: Symbol, items: &[NestedMet
         cx,
         ALLOW_ATTRIBUTES_WITHOUT_REASON,
         attr.span,
-        &format!("`{}` attribute without specifying a reason", name.as_str()),
+        format!("`{}` attribute without specifying a reason", name.as_str()),
         None,
         "try adding a reason at the end with `, reason = \"..\"`",
     );

clippy_lints/src/attrs/inline_always.rs

@@ -21,7 +21,7 @@ pub(super) fn check(cx: &LateContext<'_>, span: Span, name: Symbol, attrs: &[Att
                     cx,
                     INLINE_ALWAYS,
                     attr.span,
-                    &format!("you have declared `#[inline(always)]` on `{name}`. This is usually a bad idea"),
+                    format!("you have declared `#[inline(always)]` on `{name}`. This is usually a bad idea"),
                 );
             }
         }

clippy_lints/src/attrs/maybe_misused_cfg.rs

@@ -40,7 +40,7 @@ fn check_nested_misused_cfg(cx: &EarlyContext<'_>, items: &[NestedMetaItem]) {
                     cx,
                     MAYBE_MISUSED_CFG,
                     meta.span,
-                    &format!("'test' may be misspelled as '{}'", ident.name.as_str()),
+                    format!("'test' may be misspelled as '{}'", ident.name.as_str()),
                     "did you mean",
                     "test".to_string(),
                     Applicability::MaybeIncorrect,

clippy_lints/src/attrs/unnecessary_clippy_cfg.rs

@@ -58,7 +58,7 @@ pub(super) fn check(
                 clippy_lints,
                 "no need to put clippy lints behind a `clippy` cfg",
                 None,
-                &format!(
+                format!(
                     "write instead: `#{}[{}({})]`",
                     if attr.style == AttrStyle::Inner { "!" } else { "" },
                     ident.name,

clippy_lints/src/await_holding_invalid.rs

@@ -267,7 +267,7 @@ fn emit_invalid_type(cx: &LateContext<'_>, span: Span, disallowed: &DisallowedPa
         cx,
         AWAIT_HOLDING_INVALID_TYPE,
         span,
-        &format!(
+        format!(
             "`{}` may not be held across an `await` point per `clippy.toml`",
             disallowed.path()
         ),

clippy_lints/src/blocks_in_conditions.rs

@@ -72,7 +72,7 @@ impl<'tcx> LateLintPass<'tcx> for BlocksInConditions {
         else {
             return;
         };
-        let complex_block_message = &format!(
+        let complex_block_message = format!(
             "in {desc}, avoid complex blocks or closures with blocks; \
             instead, move the block or closure higher and bind it with a `let`",
         );
@@ -141,7 +141,7 @@ impl<'tcx> LateLintPass<'tcx> for BlocksInConditions {
                     let ex = &body.value;
                     if let ExprKind::Block(block, _) = ex.kind {
                         if !body.value.span.from_expansion() && !block.stmts.is_empty() {
-                            span_lint(cx, BLOCKS_IN_CONDITIONS, ex.span, complex_block_message);
+                            span_lint(cx, BLOCKS_IN_CONDITIONS, ex.span, complex_block_message.clone());
                             return ControlFlow::Continue(Descend::No);
                         }
                     }

clippy_lints/src/bool_assert_comparison.rs

@@ -121,7 +121,7 @@ impl<'tcx> LateLintPass<'tcx> for BoolAssertComparison {
             cx,
             BOOL_ASSERT_COMPARISON,
             macro_call.span,
-            &format!("used `{macro_name}!` with a literal bool"),
+            format!("used `{macro_name}!` with a literal bool"),
             |diag| {
                 // assert_eq!(...)
                 // ^^^^^^^^^