Fix line numbers for MIR inlined code

compiler/rustc_middle/src/ty/mod.rs

@@ -2522,7 +2522,9 @@ impl<'tcx> TyCtxt<'tcx> {
             && 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 @@ impl Span {
         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 @@ impl Span {
         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

@@ -0,0 +1,25 @@
+// compile-flags: -O -g
+
+#![crate_type = "lib"]
+
+#[inline(always)]
+fn foo() {
+    bar();
+}
+
+#[inline(never)]
+#[no_mangle]
+fn bar() {
+    panic!();
+}
+
+#[no_mangle]
+pub fn example() {
+    foo();
+}
+
+// CHECK-LABEL: @example
+// CHECK:   tail call void @bar(), !dbg [[DBG_ID:![0-9]+]]
+// CHECK: [[DBG_ID]] = !DILocation(line: 7,
+// CHECK-SAME:                     inlinedAt: [[INLINE_ID:![0-9]+]])
+// CHECK: [[INLINE_ID]] = !DILocation(line: 18,