debuginfo: Stabilize -Z debug-macros, -Z collapse-macro-debuginfo and #[collapse_debuginfo]

`-Z debug-macros` is "stabilized" by enabling it by default and removing.

`-Z collapse-macro-debuginfo` is stabilized as `-C collapse-macro-debuginfo`.
It now supports all typical boolean values (`parse_opt_bool`) in addition to just yes/no.

Default value of `collapse_debuginfo` was changed from `false` to `external` (i.e. collapsed if external, not collapsed if local).
`#[collapse_debuginfo]` attribute without a value is no longer supported to avoid guessing the default.

Author: petrochenkov

compiler/rustc_codegen_cranelift/src/debuginfo/line_info.rs

@@ -7,7 +7,7 @@ use cranelift_codegen::binemit::CodeOffset;
 use cranelift_codegen::MachSrcLoc;
 use gimli::write::{AttributeValue, FileId, FileInfo, LineProgram, LineString, LineStringTable};
 use rustc_span::{
-    FileName, Pos, SourceFile, SourceFileAndLine, SourceFileHash, SourceFileHashAlgorithm,
+    hygiene, FileName, Pos, SourceFile, SourceFileAndLine, SourceFileHash, SourceFileHashAlgorithm,
 };
 
 use crate::debuginfo::emit::address_for_func;
@@ -63,11 +63,8 @@ impl DebugContext {
         function_span: Span,
         span: Span,
     ) -> (FileId, u64, u64) {
-        // Based on https://github.com/rust-lang/rust/blob/e369d87b015a84653343032833d65d0545fd3f26/src/librustc_codegen_ssa/mir/mod.rs#L116-L131
-        // In order to have a good line stepping behavior in debugger, we overwrite debug
-        // locations of macro expansions with that of the outermost expansion site (when the macro is
-        // annotated with `#[collapse_debuginfo]` or when `-Zdebug-macros` is provided).
-        let span = tcx.collapsed_debuginfo(span, function_span);
+        // Match behavior of `FunctionCx::adjusted_span_and_dbg_scope`.
+        let span = hygiene::walk_chain_collapsed(span, function_span);
         match tcx.sess.source_map().lookup_line(span.lo()) {
             Ok(SourceFileAndLine { sf: file, line }) => {
                 let file_id = self.add_source_file(&file);

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -4,13 +4,12 @@ use rustc_index::IndexVec;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir;
 use rustc_middle::ty;
-use rustc_middle::ty::layout::TyAndLayout;
-use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
+use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_middle::ty::Instance;
 use rustc_middle::ty::Ty;
 use rustc_session::config::DebugInfo;
 use rustc_span::symbol::{kw, Symbol};
-use rustc_span::{BytePos, Span};
+use rustc_span::{hygiene, BytePos, Span};
 use rustc_target::abi::{Abi, FieldIdx, FieldsShape, Size, VariantIdx};
 
 use super::operand::{OperandRef, OperandValue};
@@ -220,26 +219,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         &self,
         source_info: mir::SourceInfo,
     ) -> Option<(Bx::DIScope, Option<Bx::DILocation>, Span)> {
-        let span = self.adjust_span_for_debugging(source_info.span);
         let scope = &self.debug_context.as_ref()?.scopes[source_info.scope];
+        let span = hygiene::walk_chain_collapsed(source_info.span, self.mir.span);
         Some((scope.adjust_dbg_scope_for_span(self.cx, span), scope.inlined_at, span))
     }
 
-    /// In order to have a good line stepping behavior in debugger, we overwrite debug
-    /// locations of macro expansions with that of the outermost expansion site (when the macro is
-    /// annotated with `#[collapse_debuginfo]` or when `-Zdebug-macros` is provided).
-    fn adjust_span_for_debugging(&self, span: Span) -> Span {
-        // Bail out if debug info emission is not enabled.
-        if self.debug_context.is_none() {
-            return span;
-        }
-        // Walk up the macro expansion chain until we reach a non-expanded span.
-        // We also stop at the function body level because no line stepping can occur
-        // at the level above that.
-        // Use span of the outermost expansion site, while keeping the original lexical scope.
-        self.cx.tcx().collapsed_debuginfo(span, self.mir.span)
-    }
-
     fn spill_operand_to_stack(
         operand: OperandRef<'tcx, Bx::Value>,
         name: Option<String>,

compiler/rustc_expand/src/base.rs

@@ -789,55 +789,50 @@ impl SyntaxExtension {
         }
     }
 
-    fn collapse_debuginfo_by_name(sess: &Session, attr: &Attribute) -> CollapseMacroDebuginfo {
-        use crate::errors::CollapseMacroDebuginfoIllegal;
-        // #[collapse_debuginfo] without enum value (#[collapse_debuginfo(no/external/yes)])
-        // considered as `yes`
-        attr.meta_item_list().map_or(CollapseMacroDebuginfo::Yes, |l| {
-            let [NestedMetaItem::MetaItem(item)] = &l[..] else {
-                sess.dcx().emit_err(CollapseMacroDebuginfoIllegal { span: attr.span });
-                return CollapseMacroDebuginfo::Unspecified;
-            };
-            if !item.is_word() {
-                sess.dcx().emit_err(CollapseMacroDebuginfoIllegal { span: item.span });
-                CollapseMacroDebuginfo::Unspecified
-            } else {
-                match item.name_or_empty() {
-                    sym::no => CollapseMacroDebuginfo::No,
-                    sym::external => CollapseMacroDebuginfo::External,
-                    sym::yes => CollapseMacroDebuginfo::Yes,
-                    _ => {
-                        sess.dcx().emit_err(CollapseMacroDebuginfoIllegal { span: item.span });
-                        CollapseMacroDebuginfo::Unspecified
-                    }
-                }
-            }
-        })
+    fn collapse_debuginfo_by_name(attr: &Attribute) -> Result<CollapseMacroDebuginfo, Span> {
+        let list = attr.meta_item_list();
+        let Some([NestedMetaItem::MetaItem(item)]) = list.as_deref() else {
+            return Err(attr.span);
+        };
+        if !item.is_word() {
+            return Err(item.span);
+        }
+
+        match item.name_or_empty() {
+            sym::no => Ok(CollapseMacroDebuginfo::No),
+            sym::external => Ok(CollapseMacroDebuginfo::External),
+            sym::yes => Ok(CollapseMacroDebuginfo::Yes),
+            _ => Err(item.path.span),
+        }
     }
 
     /// if-ext - if macro from different crate (related to callsite code)
     /// | cmd \ attr    | no  | (unspecified) | external | yes |
     /// | no            | no  | no            | no       | no  |
-    /// | (unspecified) | no  | no            | if-ext   | yes |
+    /// | (unspecified) | no  | if-ext        | if-ext   | yes |
     /// | external      | no  | if-ext        | if-ext   | yes |
     /// | yes           | yes | yes           | yes      | yes |
-    fn get_collapse_debuginfo(sess: &Session, attrs: &[ast::Attribute], is_local: bool) -> bool {
-        let mut collapse_debuginfo_attr = attr::find_by_name(attrs, sym::collapse_debuginfo)
-            .map(|v| Self::collapse_debuginfo_by_name(sess, v))
-            .unwrap_or(CollapseMacroDebuginfo::Unspecified);
-        if collapse_debuginfo_attr == CollapseMacroDebuginfo::Unspecified
-            && attr::contains_name(attrs, sym::rustc_builtin_macro)
-        {
-            collapse_debuginfo_attr = CollapseMacroDebuginfo::Yes;
-        }
-
-        let flag = sess.opts.unstable_opts.collapse_macro_debuginfo;
-        let attr = collapse_debuginfo_attr;
-        let ext = !is_local;
+    fn get_collapse_debuginfo(sess: &Session, attrs: &[ast::Attribute], ext: bool) -> bool {
+        let flag = sess.opts.cg.collapse_macro_debuginfo;
+        let attr = attr::find_by_name(attrs, sym::collapse_debuginfo)
+            .and_then(|attr| {
+                Self::collapse_debuginfo_by_name(attr)
+                    .map_err(|span| {
+                        sess.dcx().emit_err(errors::CollapseMacroDebuginfoIllegal { span })
+                    })
+                    .ok()
+            })
+            .unwrap_or_else(|| {
+                if attr::contains_name(attrs, sym::rustc_builtin_macro) {
+                    CollapseMacroDebuginfo::Yes
+                } else {
+                    CollapseMacroDebuginfo::Unspecified
+                }
+            });
         #[rustfmt::skip]
         let collapse_table = [
             [false, false, false, false],
-            [false, false, ext,   true],
+            [false, ext,   ext,   true],
             [false, ext,   ext,   true],
             [true,  true,  true,  true],
         ];
@@ -864,7 +859,7 @@ impl SyntaxExtension {
         let local_inner_macros = attr::find_by_name(attrs, sym::macro_export)
             .and_then(|macro_export| macro_export.meta_item_list())
             .is_some_and(|l| attr::list_contains_name(&l, sym::local_inner_macros));
-        let collapse_debuginfo = Self::get_collapse_debuginfo(sess, attrs, is_local);
+        let collapse_debuginfo = Self::get_collapse_debuginfo(sess, attrs, !is_local);
         tracing::debug!(?name, ?local_inner_macros, ?collapse_debuginfo, ?allow_internal_unsafe);
 
         let (builtin_name, helper_attrs) = attr::find_by_name(attrs, sym::rustc_builtin_macro)

compiler/rustc_feature/src/accepted.rs

@@ -98,6 +98,8 @@ declare_features! (
     (accepted, closure_to_fn_coercion, "1.19.0", Some(39817)),
     /// Allows using the CMPXCHG16B target feature.
     (accepted, cmpxchg16b_target_feature, "1.69.0", Some(44839)),
+    /// Allows use of the `#[collapse_debuginfo]` attribute.
+    (accepted, collapse_debuginfo, "CURRENT_RUSTC_VERSION", Some(100758)),
     /// Allows usage of the `compile_error!` macro.
     (accepted, compile_error, "1.20.0", Some(40872)),
     /// Allows `impl Trait` in function return types.

compiler/rustc_feature/src/builtin_attrs.rs

@@ -450,6 +450,9 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         template!(List: r#"natvis_file = "...", gdb_script_file = "...""#),
         DuplicatesOk, EncodeCrossCrate::No
     ),
+    ungated!(collapse_debuginfo, Normal, template!(List: "no|external|yes"), ErrorFollowing,
+        EncodeCrossCrate::Yes
+    ),
 
     // ==========================================================================
     // Unstable attributes:
@@ -516,12 +519,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         EncodeCrossCrate::Yes, experimental!(deprecated_safe),
     ),
 
-    // `#[collapse_debuginfo]`
-    gated!(
-        collapse_debuginfo, Normal, template!(Word, List: "no|external|yes"), ErrorFollowing,
-        EncodeCrossCrate::No, experimental!(collapse_debuginfo)
-    ),
-
     // RFC 2397
     gated!(
         do_not_recommend, Normal, template!(Word), WarnFollowing,

compiler/rustc_feature/src/unstable.rs

@@ -395,8 +395,6 @@ declare_features! (
     (unstable, closure_track_caller, "1.57.0", Some(87417)),
     /// Allows to use the `#[cmse_nonsecure_entry]` attribute.
     (unstable, cmse_nonsecure_entry, "1.48.0", Some(75835)),
-    /// Allows use of the `#[collapse_debuginfo]` attribute.
-    (unstable, collapse_debuginfo, "1.65.0", Some(100758)),
     /// Allows `async {}` expressions in const contexts.
     (unstable, const_async_blocks, "1.53.0", Some(85368)),
     /// Allows `const || {}` closures in const contexts.

compiler/rustc_interface/src/tests.rs

@@ -600,6 +600,7 @@ fn test_codegen_options_tracking_hash() {
     // Make sure that changing a [TRACKED] option changes the hash.
     // tidy-alphabetical-start
     tracked!(code_model, Some(CodeModel::Large));
+    tracked!(collapse_macro_debuginfo, CollapseMacroDebuginfo::Yes);
     tracked!(control_flow_guard, CFGuard::Checks);
     tracked!(debug_assertions, Some(true));
     tracked!(debuginfo, DebugInfo::Limited);
@@ -760,12 +761,10 @@ fn test_unstable_options_tracking_hash() {
         })
     );
     tracked!(codegen_backend, Some("abc".to_string()));
-    tracked!(collapse_macro_debuginfo, CollapseMacroDebuginfo::Yes);
     tracked!(coverage_options, CoverageOptions { branch: true, mcdc: true });
     tracked!(crate_attr, vec!["abc".to_string()]);
     tracked!(cross_crate_inline_threshold, InliningThreshold::Always);
     tracked!(debug_info_for_profiling, true);
-    tracked!(debug_macros, true);
     tracked!(default_hidden_visibility, Some(true));
     tracked!(dep_info_omit_d_target, true);
     tracked!(direct_access_external_data, Some(true));

compiler/rustc_middle/src/ty/mod.rs

@@ -54,7 +54,7 @@ use rustc_session::lint::LintBuffer;
 pub use rustc_session::lint::RegisteredTools;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{hygiene, ExpnId, ExpnKind, Span};
+use rustc_span::{ExpnId, ExpnKind, Span};
 use rustc_target::abi::{Align, FieldIdx, Integer, IntegerType, VariantIdx};
 pub use rustc_target::abi::{ReprFlags, ReprOptions};
 pub use rustc_type_ir::{DebugWithInfcx, InferCtxtLike, WithInfcx};
@@ -2013,22 +2013,6 @@ impl<'tcx> TyCtxt<'tcx> {
         (ident, scope)
     }
 
-    /// Returns corrected span if the debuginfo for `span` should be collapsed to the outermost
-    /// expansion site (with collapse_debuginfo attribute if the corresponding feature enabled).
-    /// Only applies when `Span` is the result of macro expansion.
-    ///
-    /// - If the `collapse_debuginfo` feature is enabled then debuginfo is not collapsed by default
-    ///   and only when a (some enclosing) macro definition is annotated with `#[collapse_debuginfo]`.
-    /// - If `collapse_debuginfo` is not enabled, then debuginfo is collapsed by default.
-    ///
-    /// When `-Zdebug-macros` is provided then debuginfo will never be collapsed.
-    pub fn collapsed_debuginfo(self, span: Span, upto: Span) -> Span {
-        if self.sess.opts.unstable_opts.debug_macros || !span.from_expansion() {
-            return span;
-        }
-        hygiene::walk_chain_collapsed(span, upto, self.features().collapse_debuginfo)
-    }
-
     #[inline]
     pub fn is_const_fn_raw(self, def_id: DefId) -> bool {
         matches!(

compiler/rustc_session/src/options.rs

@@ -1358,10 +1358,20 @@ mod parse {
         slot: &mut CollapseMacroDebuginfo,
         v: Option<&str>,
     ) -> bool {
+        if v.is_some() {
+            let mut bool_arg = None;
+            if parse_opt_bool(&mut bool_arg, v) {
+                *slot = if bool_arg.unwrap() {
+                    CollapseMacroDebuginfo::Yes
+                } else {
+                    CollapseMacroDebuginfo::No
+                };
+                return true;
+            }
+        }
+
         *slot = match v {
-            Some("no") => CollapseMacroDebuginfo::No,
             Some("external") => CollapseMacroDebuginfo::External,
-            Some("yes") => CollapseMacroDebuginfo::Yes,
             _ => return false,
         };
         true
@@ -1460,6 +1470,9 @@ options! {
         "choose the code model to use (`rustc --print code-models` for details)"),
     codegen_units: Option<usize> = (None, parse_opt_number, [UNTRACKED],
         "divide crate into N units to optimize in parallel"),
+    collapse_macro_debuginfo: CollapseMacroDebuginfo = (CollapseMacroDebuginfo::Unspecified,
+        parse_collapse_macro_debuginfo, [TRACKED],
+        "set option to collapse debuginfo for macros"),
     control_flow_guard: CFGuard = (CFGuard::Disabled, parse_cfguard, [TRACKED],
         "use Windows Control Flow Guard (default: no)"),
     debug_assertions: Option<bool> = (None, parse_opt_bool, [TRACKED],
@@ -1607,9 +1620,6 @@ options! {
         "show all expected values in check-cfg diagnostics (default: no)"),
     codegen_backend: Option<String> = (None, parse_opt_string, [TRACKED],
         "the backend to use"),
-    collapse_macro_debuginfo: CollapseMacroDebuginfo = (CollapseMacroDebuginfo::Unspecified,
-        parse_collapse_macro_debuginfo, [TRACKED],
-        "set option to collapse debuginfo for macros"),
     combine_cgu: bool = (false, parse_bool, [TRACKED],
         "combine CGUs into a single one"),
     coverage_options: CoverageOptions = (CoverageOptions::default(), parse_coverage_options, [TRACKED],
@@ -1620,8 +1630,6 @@ options! {
         "threshold to allow cross crate inlining of functions"),
     debug_info_for_profiling: bool = (false, parse_bool, [TRACKED],
         "emit discriminators and other data necessary for AutoFDO"),
-    debug_macros: bool = (false, parse_bool, [TRACKED],
-        "emit line numbers debug info inside macros (default: no)"),
     debuginfo_compression: DebugInfoCompression = (DebugInfoCompression::None, parse_debuginfo_compression, [TRACKED],
         "compress debug info sections (none, zlib, zstd, default: none)"),
     deduplicate_diagnostics: bool = (true, parse_bool, [UNTRACKED],

compiler/rustc_span/src/hygiene.rs

@@ -459,28 +459,21 @@ impl HygieneData {
         span
     }
 
-    // We need to walk up and update return span if we meet macro instantiation to be collapsed
-    fn walk_chain_collapsed(
-        &self,
-        mut span: Span,
-        to: Span,
-        collapse_debuginfo_feature_enabled: bool,
-    ) -> Span {
+    fn walk_chain_collapsed(&self, mut span: Span, to: Span) -> Span {
         let orig_span = span;
         let mut ret_span = span;
-
-        debug!(
-            "walk_chain_collapsed({:?}, {:?}), feature_enable={}",
-            span, to, collapse_debuginfo_feature_enabled,
-        );
+        debug!("walk_chain_collapsed({:?}, {:?})", span, to);
         debug!("walk_chain_collapsed: span ctxt = {:?}", span.ctxt());
-        while !span.eq_ctxt(to) && span.from_expansion() {
-            let outer_expn = self.outer_expn(span.ctxt());
+        while let ctxt = span.ctxt()
+            && !ctxt.is_root()
+            && ctxt != to.ctxt()
+        {
+            let outer_expn = self.outer_expn(ctxt);
             debug!("walk_chain_collapsed({:?}): outer_expn={:?}", span, outer_expn);
             let expn_data = self.expn_data(outer_expn);
             debug!("walk_chain_collapsed({:?}): expn_data={:?}", span, expn_data);
             span = expn_data.call_site;
-            if !collapse_debuginfo_feature_enabled || expn_data.collapse_debuginfo {
+            if expn_data.collapse_debuginfo {
                 ret_span = span;
             }
         }
@@ -604,14 +597,13 @@ pub fn walk_chain(span: Span, to: SyntaxContext) -> Span {
     HygieneData::with(|data| data.walk_chain(span, to))
 }
 
-pub fn walk_chain_collapsed(
-    span: Span,
-    to: Span,
-    collapse_debuginfo_feature_enabled: bool,
-) -> Span {
-    HygieneData::with(|hdata| {
-        hdata.walk_chain_collapsed(span, to, collapse_debuginfo_feature_enabled)
-    })
+/// In order to have good line stepping behavior in debugger, for the given span we return its
+/// outermost macro call site that still has a `#[collapse_debuginfo(yes)]` property on it.
+/// We also stop walking call sites at the function body level because no line stepping can occur
+/// at the level above that.
+/// The returned span can then be used in emitted debuginfo.
+pub fn walk_chain_collapsed(span: Span, to: Span) -> Span {
+    HygieneData::with(|data| data.walk_chain_collapsed(span, to))
 }
 
 pub fn update_dollar_crate_names(mut get_name: impl FnMut(SyntaxContext) -> Symbol) {

src/doc/rustc/src/codegen-options/index.md

@@ -42,6 +42,18 @@ generated code, but may be slower to compile.
 The default value, if not specified, is 16 for non-incremental builds. For
 incremental builds the default is 256 which allows caching to be more granular.
 
+## collapse-macro-debuginfo
+
+This flag controls whether code locations from a macro definition are collapsed into a single
+location associated with that macro's call site, when generating debuginfo for this crate.
+
+This option, if passed, overrides both default collapsing behavior and `#[collapse_debuginfo]`
+attributes in code.
+
+* `y`, `yes`, `on`, `true`: collapse code locations in debuginfo.
+* `n`, `no`, `off` or `false`: do not collapse code locations in debuginfo.
+* `external`: collapse code locations in debuginfo only if the macro comes from a different crate.
+
 ## control-flow-guard
 
 This flag controls whether LLVM enables the Windows [Control Flow