Avoid &format("...") calls in error message code.

Error message all end up passing into a function as an `impl
Into<{D,Subd}iagnosticMessage>`. If an error message is creatd as
`&format("...")` that means we allocate a string (in the `format!`
call), then take a reference, and then clone (allocating again) the
reference to produce the `{D,Subd}iagnosticMessage`, which is silly.

This commit removes the leading `&` from a lot of these cases. This
means the original `String` is moved into the
`{D,Subd}iagnosticMessage`, avoiding the double allocations. This
requires changing some function argument types from `&str` to `String`
(when all arguments are `String`) or `impl
Into<{D,Subd}iagnosticMessage>` (when some arguments are `String` and
some are `&str`).

Author: nnethercote

compiler/rustc_abi/src/layout.rs

@@ -12,7 +12,7 @@ use tracing::debug;
 pub trait LayoutCalculator {
     type TargetDataLayoutRef: Borrow<TargetDataLayout>;
 
-    fn delay_bug(&self, txt: &str);
+    fn delay_bug(&self, txt: String);
     fn current_data_layout(&self) -> Self::TargetDataLayoutRef;
 
     fn scalar_pair(&self, a: Scalar, b: Scalar) -> LayoutS {
@@ -969,7 +969,7 @@ fn univariant(
     for &i in &inverse_memory_index {
         let field = &fields[i];
         if !sized {
-            this.delay_bug(&format!(
+            this.delay_bug(format!(
                 "univariant: field #{} comes after unsized field",
                 offsets.len(),
             ));

compiler/rustc_borrowck/src/nll.rs

@@ -430,7 +430,7 @@ pub(super) fn dump_annotation<'tcx>(
 fn for_each_region_constraint<'tcx>(
     tcx: TyCtxt<'tcx>,
     closure_region_requirements: &ClosureRegionRequirements<'tcx>,
-    with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
+    with_msg: &mut dyn FnMut(String) -> io::Result<()>,
 ) -> io::Result<()> {
     for req in &closure_region_requirements.outlives_requirements {
         let subject = match req.subject {
@@ -439,7 +439,7 @@ fn for_each_region_constraint<'tcx>(
                 format!("{:?}", ty.instantiate(tcx, |vid| tcx.mk_re_var(vid)))
             }
         };
-        with_msg(&format!("where {}: {:?}", subject, req.outlived_free_region,))?;
+        with_msg(format!("where {}: {:?}", subject, req.outlived_free_region,))?;
     }
     Ok(())
 }

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -71,7 +71,7 @@ macro_rules! span_mirbug {
         $crate::type_check::mirbug(
             $context.tcx(),
             $context.last_span,
-            &format!(
+            format!(
                 "broken MIR in {:?} ({:?}): {}",
                 $context.body().source.def_id(),
                 $elem,
@@ -274,7 +274,7 @@ fn translate_outlives_facts(typeck: &mut TypeChecker<'_, '_>) {
 }
 
 #[track_caller]
-fn mirbug(tcx: TyCtxt<'_>, span: Span, msg: &str) {
+fn mirbug(tcx: TyCtxt<'_>, span: Span, msg: String) {
     // We sometimes see MIR failures (notably predicate failures) due to
     // the fact that we check rvalue sized predicates here. So use `delay_span_bug`
     // to avoid reporting bugs in those cases.

compiler/rustc_builtin_macros/src/asm.rs

@@ -550,7 +550,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
         if !parser.errors.is_empty() {
             let err = parser.errors.remove(0);
             let err_sp = template_span.from_inner(InnerSpan::new(err.span.start, err.span.end));
-            let msg = &format!("invalid asm template string: {}", err.description);
+            let msg = format!("invalid asm template string: {}", err.description);
             let mut e = ecx.struct_span_err(err_sp, msg);
             e.span_label(err_sp, err.label + " in asm template string");
             if let Some(note) = err.note {
@@ -585,7 +585,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
                                 || args.reg_args.contains(idx)
                             {
                                 let msg = format!("invalid reference to argument at index {}", idx);
-                                let mut err = ecx.struct_span_err(span, &msg);
+                                let mut err = ecx.struct_span_err(span, msg);
                                 err.span_label(span, "from here");
 
                                 let positional_args = args.operands.len()
@@ -638,7 +638,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
                                     ecx.struct_span_err(
                                         template_span
                                             .from_inner(InnerSpan::new(span.start, span.end)),
-                                        &msg,
+                                        msg,
                                     )
                                     .emit();
                                     None

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -145,7 +145,7 @@ fn cs_clone_simple(
             }
             _ => cx.span_bug(
                 trait_span,
-                &format!("unexpected substructure in simple `derive({})`", name),
+                format!("unexpected substructure in simple `derive({})`", name),
             ),
         }
     }
@@ -179,10 +179,10 @@ fn cs_clone(
             vdata = &variant.data;
         }
         EnumTag(..) | AllFieldlessEnum(..) => {
-            cx.span_bug(trait_span, &format!("enum tags in `derive({})`", name,))
+            cx.span_bug(trait_span, format!("enum tags in `derive({})`", name,))
         }
         StaticEnum(..) | StaticStruct(..) => {
-            cx.span_bug(trait_span, &format!("associated function in `derive({})`", name))
+            cx.span_bug(trait_span, format!("associated function in `derive({})`", name))
         }
     }
 
@@ -194,7 +194,7 @@ fn cs_clone(
                     let Some(ident) = field.name else {
                         cx.span_bug(
                             trait_span,
-                            &format!("unnamed field in normal struct in `derive({})`", name,),
+                            format!("unnamed field in normal struct in `derive({})`", name,),
                         );
                     };
                     let call = subcall(cx, field);

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -1591,7 +1591,7 @@ impl<'a> TraitDef<'a> {
                                 BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
                                 sp,
                                 ast::CRATE_NODE_ID,
-                                &format!(
+                                format!(
                                     "{} slice in a packed struct that derives a built-in trait",
                                     ty
                                 ),

compiler/rustc_builtin_macros/src/format.rs

@@ -814,7 +814,7 @@ fn report_invalid_references(
         };
         e = ecx.struct_span_err(
             span,
-            &format!("invalid reference to positional {} ({})", arg_list, num_args_desc),
+            format!("invalid reference to positional {} ({})", arg_list, num_args_desc),
         );
         e.note("positional arguments are zero-based");
     }

compiler/rustc_builtin_macros/src/source_util.rs

@@ -188,12 +188,12 @@ pub fn expand_include_str(
                 base::MacEager::expr(cx.expr_str(sp, interned_src))
             }
             Err(_) => {
-                cx.span_err(sp, &format!("{} wasn't a utf-8 file", file.display()));
+                cx.span_err(sp, format!("{} wasn't a utf-8 file", file.display()));
                 DummyResult::any(sp)
             }
         },
         Err(e) => {
-            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
+            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
             DummyResult::any(sp)
         }
     }
@@ -221,7 +221,7 @@ pub fn expand_include_bytes(
             base::MacEager::expr(expr)
         }
         Err(e) => {
-            cx.span_err(sp, &format!("couldn't read {}: {}", file.display(), e));
+            cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
             DummyResult::any(sp)
         }
     }

compiler/rustc_codegen_cranelift/src/pretty_clif.rs

@@ -227,7 +227,7 @@ pub(crate) fn write_ir_file(
         // Using early_warn as no Session is available here
         rustc_session::early_warn(
             rustc_session::config::ErrorOutputType::default(),
-            &format!("error writing ir file: {}", err),
+            format!("error writing ir file: {}", err),
         );
     }
 }

compiler/rustc_driver_impl/src/args.rs

@@ -25,7 +25,7 @@ pub fn arg_expand_all(at_args: &[String]) -> Vec<String> {
             Ok(arg) => args.extend(arg),
             Err(err) => rustc_session::early_error(
                 rustc_session::config::ErrorOutputType::default(),
-                &format!("Failed to load argument file: {err}"),
+                format!("Failed to load argument file: {err}"),
             ),
         }
     }

compiler/rustc_driver_impl/src/lib.rs

@@ -322,7 +322,7 @@ fn run_compiler(
             1 => panic!("make_input should have provided valid inputs"),
             _ => early_error(
                 config.opts.error_format,
-                &format!(
+                format!(
                     "multiple input filenames provided (first two filenames are `{}` and `{}`)",
                     matches.free[0], matches.free[1],
                 ),
@@ -527,7 +527,7 @@ fn handle_explain(registry: Registry, code: &str, output: ErrorOutputType) {
             }
         }
         Err(InvalidErrorCode) => {
-            early_error(output, &format!("{code} is not a valid error code"));
+            early_error(output, format!("{code} is not a valid error code"));
         }
     }
 }
@@ -1102,7 +1102,7 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
                 .map(|(flag, _)| format!("{e}. Did you mean `-{flag} {opt}`?")),
             _ => None,
         };
-        early_error(ErrorOutputType::default(), &msg.unwrap_or_else(|| e.to_string()));
+        early_error(ErrorOutputType::default(), msg.unwrap_or_else(|| e.to_string()));
     });
 
     // For all options we just parsed, we check a few aspects:
@@ -1250,7 +1250,7 @@ pub fn install_ice_hook(bug_report_url: &'static str, extra_info: fn(&Handler))
         #[cfg(windows)]
         if let Some(msg) = info.payload().downcast_ref::<String>() {
             if msg.starts_with("failed printing to stdout: ") && msg.ends_with("(os error 232)") {
-                early_error_no_abort(ErrorOutputType::default(), &msg);
+                early_error_no_abort(ErrorOutputType::default(), msg.as_str());
                 return;
             }
         };
@@ -1342,7 +1342,7 @@ pub fn init_rustc_env_logger() {
 /// other than `RUSTC_LOG`.
 pub fn init_env_logger(env: &str) {
     if let Err(error) = rustc_log::init_env_logger(env) {
-        early_error(ErrorOutputType::default(), &error.to_string());
+        early_error(ErrorOutputType::default(), error.to_string());
     }
 }
 
@@ -1409,7 +1409,7 @@ pub fn main() -> ! {
                 arg.into_string().unwrap_or_else(|arg| {
                     early_error(
                         ErrorOutputType::default(),
-                        &format!("argument {i} is not valid Unicode: {arg:?}"),
+                        format!("argument {i} is not valid Unicode: {arg:?}"),
                     )
                 })
             })

compiler/rustc_expand/src/base.rs

@@ -15,7 +15,8 @@ use rustc_attr::{self as attr, Deprecation, Stability};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::{self, Lrc};
 use rustc_errors::{
-    Applicability, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic, MultiSpan, PResult,
+    Applicability, DiagnosticBuilder, DiagnosticMessage, ErrorGuaranteed, IntoDiagnostic,
+    MultiSpan, PResult,
 };
 use rustc_lint_defs::builtin::PROC_MACRO_BACK_COMPAT;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiagnostics, RegisteredTools};
@@ -1110,7 +1111,7 @@ impl<'a> ExtCtxt<'a> {
     pub fn struct_span_err<S: Into<MultiSpan>>(
         &self,
         sp: S,
-        msg: &str,
+        msg: impl Into<DiagnosticMessage>,
     ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
         self.sess.parse_sess.span_diagnostic.struct_span_err(sp, msg)
     }
@@ -1132,14 +1133,14 @@ impl<'a> ExtCtxt<'a> {
     /// Compilation will be stopped in the near future (at the end of
     /// the macro expansion phase).
     #[rustc_lint_diagnostics]
-    pub fn span_err<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
+    pub fn span_err<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
         self.sess.parse_sess.span_diagnostic.span_err(sp, msg);
     }
     #[rustc_lint_diagnostics]
-    pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
+    pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) {
         self.sess.parse_sess.span_diagnostic.span_warn(sp, msg);
     }
-    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
+    pub fn span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: impl Into<DiagnosticMessage>) -> ! {
         self.sess.parse_sess.span_diagnostic.span_bug(sp, msg);
     }
     pub fn trace_macros_diag(&mut self) {

compiler/rustc_expand/src/expand.rs

@@ -1664,7 +1664,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         &UNUSED_ATTRIBUTES,
                         attr.span,
                         self.cx.current_expansion.lint_node_id,
-                        &format!("unused attribute `{}`", attr_name),
+                        format!("unused attribute `{}`", attr_name),
                         BuiltinLintDiagnostics::UnusedBuiltinAttribute {
                             attr_name,
                             macro_name: pprust::path_to_string(&call.path),

compiler/rustc_expand/src/mbe/diagnostics.rs

@@ -48,7 +48,7 @@ pub(super) fn failed_to_match_macro<'cx>(
 
     let span = token.span.substitute_dummy(sp);
 
-    let mut err = cx.struct_span_err(span, &parse_failure_msg(&token));
+    let mut err = cx.struct_span_err(span, parse_failure_msg(&token));
     err.span_label(span, label);
     if !def_span.is_dummy() && !cx.source_map().is_imported(def_span) {
         err.span_label(cx.source_map().guess_head_span(def_span), "when calling this macro");
@@ -170,7 +170,7 @@ impl<'a, 'cx, 'matcher> Tracker<'matcher> for CollectTrackerAndEmitter<'a, 'cx,
             }
             Error(err_sp, msg) => {
                 let span = err_sp.substitute_dummy(self.root_span);
-                self.cx.struct_span_err(span, msg).emit();
+                self.cx.struct_span_err(span, msg.as_str()).emit();
                 self.result = Some(DummyResult::any(span));
             }
             ErrorReported(_) => self.result = Some(DummyResult::any(self.root_span)),

compiler/rustc_expand/src/mbe/macro_check.rs

@@ -110,7 +110,7 @@ use crate::mbe::{KleeneToken, TokenTree};
 use rustc_ast::token::{Delimiter, Token, TokenKind};
 use rustc_ast::{NodeId, DUMMY_NODE_ID};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::MultiSpan;
+use rustc_errors::{DiagnosticMessage, MultiSpan};
 use rustc_session::lint::builtin::{META_VARIABLE_MISUSE, MISSING_FRAGMENT_SPECIFIER};
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::kw;
@@ -593,7 +593,7 @@ fn check_ops_is_prefix(
             return;
         }
     }
-    buffer_lint(sess, span.into(), node_id, &format!("unknown macro variable `{}`", name));
+    buffer_lint(sess, span.into(), node_id, format!("unknown macro variable `{}`", name));
 }
 
 /// Returns whether `binder_ops` is a prefix of `occurrence_ops`.
@@ -626,7 +626,7 @@ fn ops_is_prefix(
         if i >= occurrence_ops.len() {
             let mut span = MultiSpan::from_span(span);
             span.push_span_label(binder.span, "expected repetition");
-            let message = &format!("variable '{}' is still repeating at this depth", name);
+            let message = format!("variable '{}' is still repeating at this depth", name);
             buffer_lint(sess, span, node_id, message);
             return;
         }
@@ -642,7 +642,12 @@ fn ops_is_prefix(
     }
 }
 
-fn buffer_lint(sess: &ParseSess, span: MultiSpan, node_id: NodeId, message: &str) {
+fn buffer_lint(
+    sess: &ParseSess,
+    span: MultiSpan,
+    node_id: NodeId,
+    message: impl Into<DiagnosticMessage>,
+) {
     // Macros loaded from other crates have dummy node ids.
     if node_id != DUMMY_NODE_ID {
         sess.buffer_lint(&META_VARIABLE_MISUSE, span, node_id, message);

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -510,7 +510,7 @@ fn out_of_bounds_err<'a>(
              must be less than {max}"
         )
     };
-    cx.struct_span_err(span, &msg)
+    cx.struct_span_err(span, msg)
 }
 
 fn transcribe_metavar_expr<'a>(

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -24,7 +24,7 @@ fn generic_arg_mismatch_err(
     arg: &GenericArg<'_>,
     param: &GenericParamDef,
     possible_ordering_error: bool,
-    help: Option<&str>,
+    help: Option<String>,
 ) -> ErrorGuaranteed {
     let sess = tcx.sess;
     let mut err = struct_span_err!(
@@ -300,7 +300,7 @@ pub fn create_substs_for_generic_args<'tcx, 'a>(
                                     arg,
                                     param,
                                     !args_iter.clone().is_sorted_by_key(|arg| arg.to_ord()),
-                                    Some(&format!(
+                                    Some(format!(
                                         "reorder the arguments: {}: `<{}>`",
                                         param_types_present
                                             .into_iter()