Auto merge of #68407 - eddyb:iter-macro-backtrace, r=petrochenkov

rustc_span: return an impl Iterator instead of a Vec from macro_backtrace.

Having `Span::macro_backtrace` produce an `impl Iterator<Item = ExpnData>` allows #67359 to use it instead of rolling its own similar functionality.

The move from `MacroBacktrace` to `ExpnData` (which the first two commits are prerequisites for) both eliminates unnecessary allocations, and is strictly more flexible (exposes more information).

r? @petrochenkov

2 files changed, 16 insertions, 15 deletions

diff --git a/src/librustc_errors/emitter.rs b/src/librustc_errors/emitter.rs
index 7218730538a..f9e23e96fa8 100644
--- a/src/librustc_errors/emitter.rs
+++ b/src/librustc_errors/emitter.rs
@@ -21,6 +21,7 @@ use crate::{
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
+use rustc_span::hygiene::{ExpnKind, MacroKind};
 use std::borrow::Cow;
 use std::cmp::{max, min, Reverse};
 use std::io;
@@ -342,19 +343,20 @@ pub trait Emitter {
             if call_sp != *sp && !always_backtrace {
                 before_after.push((*sp, call_sp));
             }
-            let backtrace_len = sp.macro_backtrace().len();
-            for (i, trace) in sp.macro_backtrace().iter().rev().enumerate() {
+            let macro_backtrace: Vec<_> = sp.macro_backtrace().collect();
+            let backtrace_len = macro_backtrace.len();
+            for (i, trace) in macro_backtrace.iter().rev().enumerate() {
                 // Only show macro locations that are local
                 // and display them like a span_note
-                if trace.def_site_span.is_dummy() {
+                if trace.def_site.is_dummy() {
                     continue;
                 }
                 if always_backtrace {
                     new_labels.push((
-                        trace.def_site_span,
+                        trace.def_site,
                         format!(
                             "in this expansion of `{}`{}",
-                            trace.macro_decl_name,
+                            trace.kind.descr(),
                             if backtrace_len > 2 {
                                 // if backtrace_len == 1 it'll be pointed
                                 // at by "in this macro invocation"
@@ -366,9 +368,8 @@ pub trait Emitter {
                     ));
                 }
                 // Check to make sure we're not in any <*macros>
-                if !sm.span_to_filename(trace.def_site_span).is_macros()
-                    && !trace.macro_decl_name.starts_with("desugaring of ")
-                    && !trace.macro_decl_name.starts_with("#[")
+                if !sm.span_to_filename(trace.def_site).is_macros()
+                    && matches!(trace.kind, ExpnKind::Macro(MacroKind::Bang, _))
                     || always_backtrace
                 {
                     new_labels.push((
@@ -398,8 +399,7 @@ pub trait Emitter {
                 continue;
             }
             if sm.span_to_filename(sp_label.span.clone()).is_macros() && !always_backtrace {
-                let v = sp_label.span.macro_backtrace();
-                if let Some(use_site) = v.last() {
+                if let Some(use_site) = sp_label.span.macro_backtrace().last() {
                     before_after.push((sp_label.span.clone(), use_site.call_site.clone()));
                 }
             }
diff --git a/src/librustc_errors/json.rs b/src/librustc_errors/json.rs
index 29d3122636e..3ddf9b09893 100644
--- a/src/librustc_errors/json.rs
+++ b/src/librustc_errors/json.rs
@@ -17,7 +17,8 @@ use crate::{Applicability, DiagnosticId};
 use crate::{CodeSuggestion, SubDiagnostic};
 
 use rustc_data_structures::sync::Lrc;
-use rustc_span::{MacroBacktrace, MultiSpan, Span, SpanLabel};
+use rustc_span::hygiene::ExpnData;
+use rustc_span::{MultiSpan, Span, SpanLabel};
 use std::io::{self, Write};
 use std::path::Path;
 use std::sync::{Arc, Mutex};
@@ -308,7 +309,7 @@ impl DiagnosticSpan {
         // backtrace ourselves, but the `macro_backtrace` helper makes
         // some decision, such as dropping some frames, and I don't
         // want to duplicate that logic here.
-        let backtrace = span.macro_backtrace().into_iter();
+        let backtrace = span.macro_backtrace();
         DiagnosticSpan::from_span_full(span, is_primary, label, suggestion, backtrace, je)
     }
 
@@ -317,7 +318,7 @@ impl DiagnosticSpan {
         is_primary: bool,
         label: Option<String>,
         suggestion: Option<(&String, Applicability)>,
-        mut backtrace: vec::IntoIter<MacroBacktrace>,
+        mut backtrace: impl Iterator<Item = ExpnData>,
         je: &JsonEmitter,
     ) -> DiagnosticSpan {
         let start = je.sm.lookup_char_pos(span.lo());
@@ -325,10 +326,10 @@ impl DiagnosticSpan {
         let backtrace_step = backtrace.next().map(|bt| {
             let call_site = Self::from_span_full(bt.call_site, false, None, None, backtrace, je);
             let def_site_span =
-                Self::from_span_full(bt.def_site_span, false, None, None, vec![].into_iter(), je);
+                Self::from_span_full(bt.def_site, false, None, None, vec![].into_iter(), je);
             Box::new(DiagnosticSpanMacroExpansion {
                 span: call_site,
-                macro_decl_name: bt.macro_decl_name,
+                macro_decl_name: bt.kind.descr(),
                 def_site_span,
             })
         });