ssa: implement `#[collapse_debuginfo]`

Debuginfo line information for macro invocations are collapsed by
default - line information are replaced by the line of the outermost
expansion site. Using `-Zdebug-macros` disables this behaviour.

When the `collapse_debuginfo` feature is enabled, the default behaviour
is reversed so that debuginfo is not collapsed by default. In addition,
the `#[collapse_debuginfo]` attribute is available and can be applied to
macro definitions which will then have their line information collapsed.

Signed-off-by: David Wood <david.wood@huawei.com>

3 files changed, 24 insertions, 12 deletions

diff --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index e8ddb4ed17a..191186af6fa 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/compiler/rustc_span/src/hygiene.rs
@@ -944,12 +944,6 @@ pub struct ExpnData {
     /// internally without forcing the whole crate to opt-in
     /// to them.
     pub allow_internal_unstable: Option<Lrc<[Symbol]>>,
-    /// Whether the macro is allowed to use `unsafe` internally
-    /// even if the user crate has `#![forbid(unsafe_code)]`.
-    pub allow_internal_unsafe: bool,
-    /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`)
-    /// for a given macro.
-    pub local_inner_macros: bool,
     /// Edition of the crate in which the macro is defined.
     pub edition: Edition,
     /// The `DefId` of the macro being invoked,
@@ -957,6 +951,13 @@ pub struct ExpnData {
     pub macro_def_id: Option<DefId>,
     /// The normal module (`mod`) in which the expanded macro was defined.
     pub parent_module: Option<DefId>,
+    /// Suppresses the `unsafe_code` lint for code produced by this macro.
+    pub allow_internal_unsafe: bool,
+    /// Enables the macro helper hack (`ident!(...)` -> `$crate::ident!(...)`) for this macro.
+    pub local_inner_macros: bool,
+    /// Should debuginfo for the macro be collapsed to the outermost expansion site (in other
+    /// words, was the macro definition annotated with `#[collapse_debuginfo]`)?
+    pub collapse_debuginfo: bool,
 }
 
 impl !PartialEq for ExpnData {}
@@ -969,11 +970,12 @@ impl ExpnData {
         call_site: Span,
         def_site: Span,
         allow_internal_unstable: Option<Lrc<[Symbol]>>,
-        allow_internal_unsafe: bool,
-        local_inner_macros: bool,
         edition: Edition,
         macro_def_id: Option<DefId>,
         parent_module: Option<DefId>,
+        allow_internal_unsafe: bool,
+        local_inner_macros: bool,
+        collapse_debuginfo: bool,
     ) -> ExpnData {
         ExpnData {
             kind,
@@ -981,12 +983,13 @@ impl ExpnData {
             call_site,
             def_site,
             allow_internal_unstable,
-            allow_internal_unsafe,
-            local_inner_macros,
             edition,
             macro_def_id,
             parent_module,
             disambiguator: 0,
+            allow_internal_unsafe,
+            local_inner_macros,
+            collapse_debuginfo,
         }
     }
 
@@ -1004,12 +1007,13 @@ impl ExpnData {
             call_site,
             def_site: DUMMY_SP,
             allow_internal_unstable: None,
-            allow_internal_unsafe: false,
-            local_inner_macros: false,
             edition,
             macro_def_id,
             parent_module,
             disambiguator: 0,
+            allow_internal_unsafe: false,
+            local_inner_macros: false,
+            collapse_debuginfo: false,
         }
     }
 
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 34e2e92bdfc..26b4ebeab1b 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -564,6 +564,13 @@ impl Span {
         self.ctxt() != SyntaxContext::root()
     }
 
+    /// Returns `true` if `span` originates in a macro's expansion where debuginfo should be
+    /// collapsed.
+    pub fn in_macro_expansion_with_collapse_debuginfo(self) -> bool {
+        let outer_expn = self.ctxt().outer_expn_data();
+        matches!(outer_expn.kind, ExpnKind::Macro(..)) && outer_expn.collapse_debuginfo
+    }
+
     /// Returns `true` if `span` originates in a derive-macro's expansion.
     pub fn in_derive_expansion(self) -> bool {
         matches!(self.ctxt().outer_expn_data().kind, ExpnKind::Macro(MacroKind::Derive, _))
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 75b1dfc856a..e69a7d2ab34 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -487,6 +487,7 @@ symbols! {
         cmse_nonsecure_entry,
         coerce_unsized,
         cold,
+        collapse_debuginfo,
         column,
         column_macro,
         compare_and_swap,