Do not suggest using -Zmacro-backtrace for builtin macros

For macros that are implemented on the compiler, or that are annotated with `rustc_diagnostic_item`, which have arbitrary implementations from the point of view of the user and might as well be intrinsics, we do *not* mention the `-Zmacro-backtrace` flag. This includes `derive`s and standard macros like `panic!` and `format!`.

Author: estebank

compiler/rustc_errors/src/emitter.rs

@@ -297,7 +297,9 @@ pub trait Emitter: Translate {
                     // are some which do actually involve macros.
                     ExpnKind::Desugaring(..) | ExpnKind::AstPass(..) => None,
 
-                    ExpnKind::Macro(macro_kind, name) => Some((macro_kind, name)),
+                    ExpnKind::Macro(macro_kind, name) => {
+                        Some((macro_kind, name, expn_data.builtin_macro))
+                    }
                 }
             })
             .collect();
@@ -309,13 +311,18 @@ pub trait Emitter: Translate {
         self.render_multispans_macro_backtrace(span, children, backtrace);
 
         if !backtrace {
-            if let Some((macro_kind, name)) = has_macro_spans.first() {
+            // Skip builtin macros, as their expansion isn't relevant to the end user. This includes
+            // actual intrinsics, like `asm!`, as well as macros by example, like `println!`, which
+            // might as well be an intrinsic as far as the user is concerned.
+            if let Some((macro_kind, name, _)) = has_macro_spans.first()
+                && let Some((_, _, false)) = has_macro_spans.last()
+            {
                 // Mark the actual macro this originates from
-                let and_then = if let Some((macro_kind, last_name)) = has_macro_spans.last()
+                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}`",)
+                    format!(" which comes from the expansion of the {descr} `{last_name}`")
                 } else {
                     "".to_string()
                 };

compiler/rustc_expand/src/base.rs

@@ -757,6 +757,11 @@ pub struct SyntaxExtension {
     /// Built-in macros have a couple of special properties like availability
     /// in `#[no_implicit_prelude]` modules, so we have to keep this flag.
     pub builtin_name: Option<Symbol>,
+    /// Whether this macro is either a compiler intrinsic (implied by the above field) or a macro
+    /// provided by the standard library where the specific of its implementation are not relevant
+    /// to the end user, like for `format!` or `println!`, which are normal macros by example, but
+    /// that is an implementation detail.
+    pub builtin: bool,
     /// Suppresses the `unsafe_code` lint for code produced by this macro.
     pub allow_internal_unsafe: bool,
     /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) for this macro.
@@ -792,6 +797,7 @@ impl SyntaxExtension {
             helper_attrs: Vec::new(),
             edition,
             builtin_name: None,
+            builtin: false,
             kind,
             allow_internal_unsafe: false,
             local_inner_macros: false,
@@ -888,17 +894,19 @@ impl SyntaxExtension {
                 )
             })
             .unwrap_or_else(|| (None, helper_attrs));
+        let builtin = builtin_name.is_some()
+            || ast::attr::find_by_name(attrs, sym::rustc_diagnostic_item).is_some();
 
-        let stability = find_attr!(attrs, AttributeKind::Stability{stability, ..} => *stability);
+        let stability = find_attr!(attrs, AttributeKind::Stability { stability, .. } => *stability);
 
         // FIXME(jdonszelmann): make it impossible to miss the or_else in the typesystem
-        if let Some(sp) = find_attr!(attrs, AttributeKind::ConstStability{span, ..} => *span) {
+        if let Some(sp) = find_attr!(attrs, AttributeKind::ConstStability { span, .. } => *span) {
             sess.dcx().emit_err(errors::MacroConstStability {
                 span: sp,
                 head_span: sess.source_map().guess_head_span(span),
             });
         }
-        if let Some(sp) = find_attr!(attrs, AttributeKind::BodyStability{span, ..} => *span) {
+        if let Some(sp) = find_attr!(attrs, AttributeKind::BodyStability{ span, .. } => *span) {
             sess.dcx().emit_err(errors::MacroBodyStability {
                 span: sp,
                 head_span: sess.source_map().guess_head_span(span),
@@ -912,10 +920,14 @@ impl SyntaxExtension {
                 // FIXME(jdonszelmann): avoid the into_iter/collect?
                 .then(|| allow_internal_unstable.iter().map(|i| i.0).collect::<Vec<_>>().into()),
             stability,
-            deprecation: find_attr!(attrs, AttributeKind::Deprecation{deprecation, ..} => *deprecation),
+            deprecation: find_attr!(
+                attrs,
+                AttributeKind::Deprecation { deprecation, .. } => *deprecation
+            ),
             helper_attrs,
             edition,
             builtin_name,
+            builtin,
             allow_internal_unsafe,
             local_inner_macros,
             collapse_debuginfo,
@@ -1000,6 +1012,7 @@ impl SyntaxExtension {
             self.allow_internal_unsafe,
             self.local_inner_macros,
             self.collapse_debuginfo,
+            self.builtin,
         )
     }
 }