diagnostics: hide expansion of builtin-like macros

compiler/rustc_errors/src/emitter.rs

@@ -24,7 +24,7 @@ use rustc_lexer;
 use rustc_lint_defs::pluralize;
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use rustc_span::source_map::SourceMap;
-use rustc_span::{FileLines, FileName, SourceFile, Span, char_width, str_width};
+use rustc_span::{FileLines, FileName, SourceFile, Span, char_width, str_width, sym};
 use termcolor::{Buffer, BufferWriter, Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
 use tracing::{debug, instrument, trace, warn};
 
@@ -298,7 +298,17 @@ pub trait Emitter: Translate {
                     ExpnKind::Desugaring(..) | ExpnKind::AstPass(..) => None,
 
                     ExpnKind::Macro(macro_kind, name) => {
-                        Some((macro_kind, name, expn_data.hide_backtrace))
+                        // Don't recommend using `-Zmacro-backtrace` if
+                        // - hide_backtrace is true, which it is for builtin macros
+                        // - if the macro uses internal features so their expansion is unlikely to be useful
+                        let hide_macro_backtrace_suggestion = expn_data.hide_backtrace
+                            || expn_data.allow_internal_unstable.is_some_and(|aiu| {
+                                aiu.contains(&sym::fmt_internals)
+                                    || aiu.contains(&sym::print_internals)
+                                    || aiu.contains(&sym::liballoc_internals)
+                            });
+
+                        Some((macro_kind, name, hide_macro_backtrace_suggestion))
                     }
                 }
             })
@@ -311,8 +321,9 @@ pub trait Emitter: Translate {
         self.render_multispans_macro_backtrace(span, children, backtrace);
 
         if !backtrace {
-            // Skip builtin macros, as their expansion isn't relevant to the end user. This includes
-            // actual intrinsics, like `asm!`.
+            // Skip some special macros, as their expansion isn't relevant to the end user.
+            // This includes actual intrinsics and builtins like `asm!`, as well as macros
+            // that contain implementation details like the formatting macros
             if let Some((macro_kind, name, _)) = has_macro_spans.first()
                 && let Some((_, _, false)) = has_macro_spans.last()
             {

compiler/rustc_span/src/symbol.rs

@@ -1007,6 +1007,7 @@ symbols! {
         fmaf64,
         fmt,
         fmt_debug,
+        fmt_internals,
         fmul_algebraic,
         fmul_fast,
         fmuladdf128,
@@ -1240,6 +1241,7 @@ symbols! {
         let_else,
         lhs,
         lib,
+        liballoc_internals,
         libc,
         lifetime,
         lifetime_capture_rules_2024,
@@ -1623,6 +1625,7 @@ symbols! {
         prelude_import,
         preserves_flags,
         prfchw_target_feature,
+        print_internals,
         print_macro,
         println_macro,
         proc_dash_macro: "proc-macro",

src/tools/miri/tests/fail/dangling_pointers/out_of_bounds_read.stderr

@@ -13,7 +13,6 @@ LL |     let v: Vec<u16> = vec![1, 2];
    |                       ^^^^^^^^^^
    = note: BACKTRACE (of the first span):
    = note: inside `main` at tests/fail/dangling_pointers/out_of_bounds_read.rs:LL:CC
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 

src/tools/miri/tests/fail/dangling_pointers/out_of_bounds_write.stderr

@@ -13,7 +13,6 @@ LL |     let mut v: Vec<u16> = vec![1, 2];
    |                           ^^^^^^^^^^
    = note: BACKTRACE (of the first span):
    = note: inside `main` at tests/fail/dangling_pointers/out_of_bounds_write.rs:LL:CC
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 

src/tools/miri/tests/fail/erroneous_const2.stderr

@@ -23,8 +23,6 @@ note: erroneous constant encountered
    |
 LL |     println!("{}", FOO);
    |                    ^^^
-   |
-   = note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

src/tools/miri/tests/fail/intrinsics/simd-scatter.stderr

@@ -18,7 +18,6 @@ LL |         let mut vec: Vec<i8> = vec![10, 11, 12, 13, 14, 15, 16, 17, 18];
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: BACKTRACE (of the first span):
    = note: inside `main` at tests/fail/intrinsics/simd-scatter.rs:LL:CC
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 

src/tools/miri/tests/fail/tree_borrows/protector-write-lazy.stderr

@@ -19,7 +19,6 @@ LL | }
    = help: this transition corresponds to a loss of read and write permissions
    = note: BACKTRACE (of the first span):
    = note: inside `main` at tests/fail/tree_borrows/protector-write-lazy.rs:LL:CC
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
 

tests/rustdoc-ui/doctest/main-alongside-macro-calls.fail.stdout

@@ -13,8 +13,6 @@ error: macros that expand to items must be delimited with braces or followed by
    |
 LL | println!();
    | ^^^^^^^^^^
-   |
-   = note: this error originates in the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: macro expansion ignores `{` and any tokens following
   --> $SRC_DIR/std/src/macros.rs:LL:COL
@@ -35,8 +33,6 @@ error: macros that expand to items must be delimited with braces or followed by
    |
 LL | println!();
    | ^^^^^^^^^^
-   |
-   = note: this error originates in the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: macro expansion ignores `{` and any tokens following
   --> $SRC_DIR/std/src/macros.rs:LL:COL

tests/ui/asm/parse-error.stderr

@@ -193,16 +193,12 @@ error: asm template must be a string literal
    |
 LL |         asm!(format!("{{{}}}", 0), in(reg) foo);
    |              ^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: asm template must be a string literal
   --> $DIR/parse-error.rs:86:21
    |
 LL |         asm!("{1}", format!("{{{}}}", 0), in(reg) foo, out(reg) bar);
    |                     ^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: _ cannot be used for input operands
   --> $DIR/parse-error.rs:88:28
@@ -357,16 +353,12 @@ error: asm template must be a string literal
    |
 LL | global_asm!(format!("{{{}}}", 0), const FOO);
    |             ^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: asm template must be a string literal
   --> $DIR/parse-error.rs:143:20
    |
 LL | global_asm!("{1}", format!("{{{}}}", 0), const FOO, const BAR);
    |                    ^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: the `in` operand cannot be used with `global_asm!`
   --> $DIR/parse-error.rs:146:19

tests/ui/asm/x86_64/type-check-2.stderr

@@ -21,7 +21,6 @@ LL |         asm!("{}", in(reg) vec![0]);
    |                            ^^^^^^^
    |
    = note: only integers, floats, SIMD vectors, pointers and function pointers can be used as arguments for inline assembly
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: cannot use value of type `(i32, i32, i32)` for inline assembly
   --> $DIR/type-check-2.rs:52:28

tests/ui/async-await/unreachable-lint-2.stderr

@@ -11,7 +11,6 @@ note: the lint level is defined here
    |
 LL | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
-   = note: this error originates in the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/alias-liveness/higher-ranked-outlives-for-capture.stderr

@@ -8,8 +8,6 @@ LL |     test(&vec![])
    |     argument requires that borrow lasts for `'static`
 LL | }
    | - temporary value is freed at the end of this statement
-   |
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-and-init.stderr

@@ -8,8 +8,6 @@ LL |     println!("{}", false && { i = 5; true });
    |                               ----- binding initialized here in some conditions
 LL |     println!("{}", i);
    |                    ^ `i` used here but it is possibly-uninitialized
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-borrowed-uniq-rvalue-2.stderr

@@ -8,7 +8,6 @@ LL |     let x = defer(&vec!["Goodbye", "world!"]);
 LL |     x.x[0];
    |     ------ borrow later used here
    |
-   = note: this error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider using a `let` binding to create a longer lived value
    |
 LL ~     let binding = vec!["Goodbye", "world!"];

tests/ui/borrowck/borrowck-break-uninit-2.stderr

@@ -7,7 +7,6 @@ LL |     let x: isize;
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let x: isize = 42;

tests/ui/borrowck/borrowck-break-uninit.stderr

@@ -7,7 +7,6 @@ LL |     let x: isize;
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let x: isize = 42;

tests/ui/borrowck/borrowck-or-init.stderr

@@ -8,8 +8,6 @@ LL |     println!("{}", false || { i = 5; true });
    |                               ----- binding initialized here in some conditions
 LL |     println!("{}", i);
    |                    ^ `i` used here but it is possibly-uninitialized
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-while-break.stderr

@@ -8,8 +8,6 @@ LL |     while cond {
 ...
 LL |     println!("{}", v);
    |                    ^ `v` used here but it is possibly-uninitialized
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/issue-24267-flow-exit.stderr

@@ -7,7 +7,6 @@ LL |     loop { x = break; }
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let x: i32 = 42;
@@ -22,7 +21,6 @@ LL |     for _ in 0..10 { x = continue; }
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let x: i32 = 42;

tests/ui/borrowck/issue-47646.stderr

@@ -12,8 +12,6 @@ LL |             println!("{:?}", heap);
 ...
 LL |     };
    |      - ... and the mutable borrow might be used here, when that temporary is dropped and runs the destructor for type `(Option<PeekMut<'_, i32>>, ())`
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/issue-64453.stderr

@@ -6,7 +6,6 @@ LL | static settings_dir: String = format!("");
    |
    = note: calls in statics are limited to constant functions, tuple structs and tuple variants
    = note: consider wrapping this expression in `std::sync::LazyLock::new(|| ...)`
-   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0507]: cannot move out of static item `settings_dir`
   --> $DIR/issue-64453.rs:13:37

tests/ui/borrowck/suggest-assign-rvalue.stderr

@@ -19,7 +19,6 @@ LL |     let my_float: f32;
 LL |     println!("my_float: {}", my_float);
    |                              ^^^^^^^^ `my_float` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let my_float: f32 = 3.14159;
@@ -33,7 +32,6 @@ LL |     let demo: Demo;
 LL |     println!("demo: {:?}", demo);
    |                            ^^^^ `demo` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let demo: Demo = Default::default();
@@ -47,7 +45,6 @@ LL |     let demo_no: DemoNoDef;
 LL |     println!("demo_no: {:?}", demo_no);
    |                               ^^^^^^^ `demo_no` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let demo_no: DemoNoDef = /* value */;
@@ -61,7 +58,6 @@ LL |     let arr: [i32; 5];
 LL |     println!("arr: {:?}", arr);
    |                           ^^^ `arr` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let arr: [i32; 5] = [42; 5];
@@ -75,7 +71,6 @@ LL |     let foo: Vec<&str>;
 LL |     println!("foo: {:?}", foo);
    |                           ^^^ `foo` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let foo: Vec<&str> = vec![];
@@ -89,7 +84,6 @@ LL |     let my_string: String;
 LL |     println!("my_string: {}", my_string);
    |                               ^^^^^^^^^ `my_string` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let my_string: String = Default::default();
@@ -103,7 +97,6 @@ LL |     let my_int: &i32;
 LL |     println!("my_int: {}", *my_int);
    |                            ^^^^^^^ `*my_int` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let my_int: &i32 = &42;
@@ -117,7 +110,6 @@ LL |     let hello: &str;
 LL |     println!("hello: {}", hello);
    |                           ^^^^^ `hello` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
 LL |     let hello: &str = "";
@@ -130,8 +122,6 @@ LL |     let never: !;
    |         ----- binding declared here but left uninitialized
 LL |     println!("never: {}", never);
    |                           ^^^^^ `never` used here but it isn't initialized
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 10 previous errors
 

tests/ui/closures/2229_closure_analysis/diagnostics/arrays.stderr

@@ -53,8 +53,6 @@ LL |     println!("{}", arr[3]);
 ...
 LL |     c();
    |     - mutable borrow later used here
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0502]: cannot borrow `arr` as immutable because it is also borrowed as mutable
   --> $DIR/arrays.rs:71:24

tests/ui/closures/2229_closure_analysis/diagnostics/box.stderr

@@ -25,8 +25,6 @@ LL |     println!("{}", e.0.0.m.x);
 LL |
 LL |     c();
    |     - mutable borrow later used here
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0506]: cannot assign to `e.0.0.m.x` because it is borrowed
   --> $DIR/box.rs:55:5

tests/ui/closures/2229_closure_analysis/diagnostics/repr_packed.stderr

@@ -7,7 +7,6 @@ LL |         println!("{}", foo.x);
    = note: packed structs are only aligned by one byte, and many modern architectures penalize unaligned field accesses
    = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/closures/2229_closure_analysis/diagnostics/simple-struct-min-capture.stderr

@@ -13,8 +13,6 @@ LL |     println!("{:?}", p);
 LL |
 LL |     c();
    |     - mutable borrow later used here
-   |
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 1 previous error
 

tests/ui/closures/issue-111932.stderr

@@ -19,7 +19,6 @@ LL |         println!("{:?}", foo);
    = help: the trait `Sized` is not implemented for `dyn Foo`
 note: required by an implicit `Sized` bound in `core::fmt::rt::Argument::<'_>::new_debug`
   --> $SRC_DIR/core/src/fmt/rt.rs:LL:COL
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
 

tests/ui/codemap_tests/bad-format-args.stderr

@@ -3,8 +3,6 @@ error: requires at least a format string argument
    |
 LL |     format!();
    |     ^^^^^^^^^
-   |
-   = note: this error originates in the macro `$crate::__export::format_args` which comes from the expansion of the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: expected `,`, found `1`
   --> $DIR/bad-format-args.rs:3:16

tests/ui/codemap_tests/tab_3.stderr

@@ -11,7 +11,6 @@ LL |         println!("{:?}", some_vec);
    |
 note: `into_iter` takes ownership of the receiver `self`, which moves `some_vec`
   --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
-   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: you can `clone` the value and consume it, but this might not be your desired behavior
    |
 LL |     some_vec.clone().into_iter();