Add implicit argument to MIR of #[track_caller] functions.

Author: anp

src/librustc_mir/build/mod.rs

@@ -89,6 +89,25 @@ pub fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> Body<'_> {
                 _ => None,
             };
 
+            // if this fn has #[track_caller], it will receive an implicit argument with a location
+            let has_track_caller = tcx.codegen_fn_attrs(def_id).flags
+                .contains(hir::CodegenFnAttrFlags::TRACK_CALLER);
+            let location_argument = if has_track_caller {
+                #[cfg(not(bootstrap))]
+                {
+                    use rustc::middle::lang_items::PanicLocationLangItem;
+                    let panic_loc_item = tcx.require_lang_item(PanicLocationLangItem, None);
+                    let panic_loc_ty = tcx.type_of(panic_loc_item);
+                    Some(ArgInfo(panic_loc_ty, None, None, None))
+                }
+                #[cfg(bootstrap)]
+                {
+                    bug!("#[track_caller] can't be used during a bootstrap build (yet).");
+                }
+            } else {
+                None
+            };
+
             let safety = match fn_sig.unsafety {
                 hir::Unsafety::Normal => Safety::Safe,
                 hir::Unsafety::Unsafe => Safety::FnUnsafe,
@@ -141,7 +160,9 @@ pub fn mir_build(tcx: TyCtxt<'_>, def_id: DefId) -> Body<'_> {
                         ArgInfo(ty, opt_ty_info, Some(&arg), self_arg)
                     });
 
-            let arguments = implicit_argument.into_iter().chain(explicit_arguments);
+            let arguments = implicit_argument.into_iter()
+                .chain(location_argument)
+                .chain(explicit_arguments);
 
             let (yield_ty, return_ty) = if body.generator_kind.is_some() {
                 let gen_sig = match ty.kind {

src/test/ui/rfc-2091-track-caller/pass.rs

@@ -0,0 +1,12 @@
+// failure-status: 101
+// normalize-stderr-test "note: rustc 1.* running on .*" -> "note: rustc VERSION running on TARGET"
+// normalize-stderr-test "note: compiler flags: .*" -> "note: compiler flags: FLAGS"
+
+#![feature(track_caller)] //~ WARN the feature `track_caller` is incomplete
+
+#[track_caller]
+fn f() {}
+
+fn main() {
+    f();
+}

src/test/ui/rfc-2091-track-caller/pass.stderr

@@ -0,0 +1,21 @@
+warning: the feature `track_caller` is incomplete and may cause the compiler to crash
+  --> $DIR/should-pass.rs:5:12
+   |
+LL | #![feature(track_caller)]
+   |            ^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+
+thread 'rustc' panicked at 'index out of bounds: the len is 0 but the index is 0', $SRC_DIR/libcore/slice/mod.rs:LL:COL
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
+
+error: internal compiler error: unexpected panic
+
+note: the compiler unexpectedly panicked. this is a bug.
+
+note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
+
+note: rustc VERSION running on TARGET
+
+note: compiler flags: FLAGS
+