Fix line numbers for MIR inlined code

`should_collapse_debuginfo` detects if the specified span is part of a
macro expansion however it does this by checking if the span is anything
other than a normal (non-expanded) kind, then the span sequence is
walked backwards to the root span.

This doesn't work when the MIR inliner inlines code as it creates spans
with expansion information set to `ExprKind::Inlined` and results in the
line number being attributed to the inline callsite rather than the
normal line number of the inlined code.

compiler/rustc_middle/src/ty/mod.rs

@@ -2522,7 +2522,9 @@ pub fn should_collapse_debuginfo(self, span: Span) -> bool {
             && if self.features().collapse_debuginfo {
                 span.in_macro_expansion_with_collapse_debuginfo()
             } else {
-                span.from_expansion()
+                // Inlined spans should not be collapsed as that leads to all of the
+                // inlined code being attributed to the inline callsite.
+                span.from_expansion() && !span.is_inlined()
             }
     }
 

compiler/rustc_span/src/lib.rs

@@ -558,7 +558,7 @@ pub fn is_dummy(self) -> bool {
         self.data_untracked().is_dummy()
     }
 
-    /// Returns `true` if this span comes from a macro or desugaring.
+    /// Returns `true` if this span comes from any kind of macro, desugaring or inlining.
     #[inline]
     pub fn from_expansion(self) -> bool {
         self.ctxt() != SyntaxContext::root()
@@ -571,6 +571,12 @@ pub fn in_macro_expansion_with_collapse_debuginfo(self) -> bool {
         matches!(outer_expn.kind, ExpnKind::Macro(..)) && outer_expn.collapse_debuginfo
     }
 
+    /// Returns `true` if this span comes from MIR inlining.
+    pub fn is_inlined(self) -> bool {
+        let outer_expn = self.ctxt().outer_expn_data();
+        matches!(outer_expn.kind, ExpnKind::Inlined)
+    }
+
     /// 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, _))

src/test/codegen/mir-inlined-line-numbers.rs

@@ -20,6 +20,6 @@ pub fn example() {
 
 // CHECK-LABEL: @example
 // CHECK:   tail call void @bar(), !dbg [[DBG_ID:![0-9]+]]
-// CHECK: [[DBG_ID]] = !DILocation(line: 18, 
+// CHECK: [[DBG_ID]] = !DILocation(line: 7,
 // CHECK-SAME:                     inlinedAt: [[INLINE_ID:![0-9]+]])
 // CHECK: [[INLINE_ID]] = !DILocation(line: 18,