Rollup merge of rust-lang#98320 - compiler-errors:macro-backtrace, r=estebank

Mention first and last macro in backtrace

Slight improvement to diagnostic mentioning what macro an error originates from. Not sure if it's worthwhile.

Author: Dylan-DPC

compiler/rustc_errors/src/emitter.rs

@@ -399,11 +399,11 @@ pub trait Emitter {
     ) {
         // Check for spans in macros, before `fix_multispans_in_extern_macros`
         // has a chance to replace them.
-        let has_macro_spans = iter::once(&*span)
+        let has_macro_spans: Vec<_> = iter::once(&*span)
             .chain(children.iter().map(|child| &child.span))
             .flat_map(|span| span.primary_spans())
             .flat_map(|sp| sp.macro_backtrace())
-            .find_map(|expn_data| {
+            .filter_map(|expn_data| {
                 match expn_data.kind {
                     ExpnKind::Root => None,
 
@@ -413,7 +413,8 @@ pub trait Emitter {
 
                     ExpnKind::Macro(macro_kind, name) => Some((macro_kind, name)),
                 }
-            });
+            })
+            .collect();
 
         if !backtrace {
             self.fix_multispans_in_extern_macros(source_map, span, children);
@@ -422,11 +423,22 @@ pub trait Emitter {
         self.render_multispans_macro_backtrace(span, children, backtrace);
 
         if !backtrace {
-            if let Some((macro_kind, name)) = has_macro_spans {
-                let descr = macro_kind.descr();
+            if let Some((macro_kind, name)) = has_macro_spans.first() {
+                // Mark the actual macro this originates from
+                let and_then = if let Some((macro_kind, last_name)) = has_macro_spans.last()
+                    && last_name != name
+                {
+                    let descr = macro_kind.descr();
+                    format!(
+                        " which comes from the expansion of the {descr} `{last_name}`",
+                    )
+                } else {
+                    "".to_string()
+                };
 
+                let descr = macro_kind.descr();
                 let msg = format!(
-                    "this {level} originates in the {descr} `{name}` \
+                    "this {level} originates in the {descr} `{name}`{and_then} \
                     (in Nightly builds, run with -Z macro-backtrace for more info)",
                 );
 

compiler/rustc_errors/src/lib.rs

@@ -6,6 +6,7 @@
 #![feature(drain_filter)]
 #![feature(backtrace)]
 #![feature(if_let_guard)]
+#![cfg_attr(bootstrap, feature(let_chains))]
 #![feature(let_else)]
 #![feature(never_type)]
 #![feature(adt_const_params)]

src/test/ui/borrowck/borrowck-and-init.stderr

@@ -9,7 +9,7 @@ LL |     println!("{}", false && { i = 5; true });
 LL |     println!("{}", i);
    |                    ^ `i` used here but it is possibly-uninitialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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 previous error
 

src/test/ui/borrowck/borrowck-break-uninit-2.stderr

@@ -7,7 +7,7 @@ LL |     let x: isize;
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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 previous error
 

src/test/ui/borrowck/borrowck-break-uninit.stderr

@@ -7,7 +7,7 @@ LL |     let x: isize;
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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 previous error
 

src/test/ui/borrowck/borrowck-or-init.stderr

@@ -9,7 +9,7 @@ LL |     println!("{}", false || { i = 5; true });
 LL |     println!("{}", i);
    |                    ^ `i` used here but it is possibly-uninitialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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 previous error
 

src/test/ui/borrowck/borrowck-while-break.stderr

@@ -9,7 +9,7 @@ LL |     while cond {
 LL |     println!("{}", v);
    |                    ^ `v` used here but it is possibly-uninitialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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 previous error
 

src/test/ui/borrowck/issue-24267-flow-exit.stderr

@@ -7,7 +7,7 @@ LL |     loop { x = break; }
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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[E0381]: used binding `x` isn't initialized
   --> $DIR/issue-24267-flow-exit.rs:18:20
@@ -18,7 +18,7 @@ LL |     for _ in 0..10 { x = continue; }
 LL |     println!("{}", x);
    |                    ^ `x` used here but it isn't initialized
    |
-   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = 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
 

src/test/ui/borrowck/issue-64453.stderr

@@ -5,7 +5,7 @@ LL | static settings_dir: String = format!("");
    |                               ^^^^^^^^^^^
    |
    = help: add `#![feature(const_fmt_arguments_new)]` to the crate attributes to enable
-   = note: this error originates in the macro `$crate::__export::format_args` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$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[E0015]: cannot call non-const fn `format` in statics
   --> $DIR/issue-64453.rs:4:31

src/test/ui/borrowck/issue-81899.stderr

@@ -10,7 +10,7 @@ LL |     panic!()
    |     the evaluated program panicked at 'explicit panic', $DIR/issue-81899.rs:12:5
    |     inside `f::<[closure@$DIR/issue-81899.rs:4:31: 4:34]>` at $SRC_DIR/std/src/panic.rs:LL:COL
    |
-   = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::panic::panic_2015` which comes from the expansion of the macro `panic` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: any use of this value will cause an error
   --> $DIR/issue-81899.rs:4:23