1 files changed, 93 insertions, 0 deletions
diff --git a/compiler/rustc_borrowck/src/region_infer/dump_mir.rs b/compiler/rustc_borrowck/src/region_infer/dump_mir.rs
new file mode 100644
index 000000000..fe5193102
--- /dev/null
+++ b/compiler/rustc_borrowck/src/region_infer/dump_mir.rs
@@ -0,0 +1,93 @@
+//! As part of generating the regions, if you enable `-Zdump-mir=nll`,
+//! we will generate an annotated copy of the MIR that includes the
+//! state of region inference. This code handles emitting the region
+//! context internal state.
+
+use super::{OutlivesConstraint, RegionInferenceContext};
+use crate::type_check::Locations;
+use rustc_infer::infer::NllRegionVariableOrigin;
+use rustc_middle::ty::TyCtxt;
+use std::io::{self, Write};
+
+// Room for "'_#NNNNr" before things get misaligned.
+// Easy enough to fix if this ever doesn't seem like
+// enough.
+const REGION_WIDTH: usize = 8;
+
+impl<'tcx> RegionInferenceContext<'tcx> {
+    /// Write out our state into the `.mir` files.
+    pub(crate) fn dump_mir(&self, tcx: TyCtxt<'tcx>, out: &mut dyn Write) -> io::Result<()> {
+        writeln!(out, "| Free Region Mapping")?;
+
+        for region in self.regions() {
+            if let NllRegionVariableOrigin::FreeRegion = self.definitions[region].origin {
+                let classification = self.universal_regions.region_classification(region).unwrap();
+                let outlived_by = self.universal_region_relations.regions_outlived_by(region);
+                writeln!(
+                    out,
+                    "| {r:rw$?} | {c:cw$?} | {ob:?}",
+                    r = region,
+                    rw = REGION_WIDTH,
+                    c = classification,
+                    cw = 8, // "External" at most
+                    ob = outlived_by
+                )?;
+            }
+        }
+
+        writeln!(out, "|")?;
+        writeln!(out, "| Inferred Region Values")?;
+        for region in self.regions() {
+            writeln!(
+                out,
+                "| {r:rw$?} | {ui:4?} | {v}",
+                r = region,
+                rw = REGION_WIDTH,
+                ui = self.region_universe(region),
+                v = self.region_value_str(region),
+            )?;
+        }
+
+        writeln!(out, "|")?;
+        writeln!(out, "| Inference Constraints")?;
+        self.for_each_constraint(tcx, &mut |msg| writeln!(out, "| {}", msg))?;
+
+        Ok(())
+    }
+
+    /// Debugging aid: Invokes the `with_msg` callback repeatedly with
+    /// our internal region constraints. These are dumped into the
+    /// -Zdump-mir file so that we can figure out why the region
+    /// inference resulted in the values that it did when debugging.
+    fn for_each_constraint(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        with_msg: &mut dyn FnMut(&str) -> io::Result<()>,
+    ) -> io::Result<()> {
+        for region in self.definitions.indices() {
+            let value = self.liveness_constraints.region_value_str(region);
+            if value != "{}" {
+                with_msg(&format!("{:?} live at {}", region, value))?;
+            }
+        }
+
+        let mut constraints: Vec<_> = self.constraints.outlives().iter().collect();
+        constraints.sort_by_key(|c| (c.sup, c.sub));
+        for constraint in &constraints {
+            let OutlivesConstraint { sup, sub, locations, category, span, variance_info: _ } =
+                constraint;
+            let (name, arg) = match locations {
+                Locations::All(span) => {
+                    ("All", tcx.sess.source_map().span_to_embeddable_string(*span))
+                }
+                Locations::Single(loc) => ("Single", format!("{:?}", loc)),
+            };
+            with_msg(&format!(
+                "{:?}: {:?} due to {:?} at {}({}) ({:?}",
+                sup, sub, category, name, arg, span
+            ))?;
+        }
+
+        Ok(())
+    }
+}