Recognize dyn-trait-type in Rust demangling.

PiperOrigin-RevId: 636563266
Change-Id: Id4ee907c30d7dac400f1f85776cc5f1fcb3e20b7

2 files changed, 104 insertions, 1 deletions

diff --git a/absl/debugging/internal/demangle_rust.cc b/absl/debugging/internal/demangle_rust.cc
index b8cc1803..06ee7a4b 100644
--- a/absl/debugging/internal/demangle_rust.cc
+++ b/absl/debugging/internal/demangle_rust.cc
@@ -277,7 +277,7 @@ class RustSymbolParser {
             goto type;
           }
           if (Eat('F')) goto fn_type;
-          if (Eat('D')) return false;  // dyn-trait-type not yet implemented
+          if (Eat('D')) goto dyn_trait_type;
           if (Eat('B')) goto type_backref;
           goto path;
 
@@ -349,6 +349,54 @@ class RustSymbolParser {
           --silence_depth_;
           continue;
 
+        // dyn-trait-type -> D dyn-bounds lifetime (D already consumed)
+        // dyn-bounds -> binder? dyn-trait* E
+        //
+        // The grammar strangely allows an empty trait list, even though the
+        // compiler should never output one.  We follow existing demanglers in
+        // rendering DEL_ as "dyn ".
+        //
+        // Because auto traits lengthen a type name considerably without
+        // providing much value to a search for related source code, it would be
+        // desirable to abbreviate
+        //     dyn main::Trait + std::marker::Copy + std::marker::Send
+        // to
+        //     dyn main::Trait + ...,
+        // eliding the auto traits.  But it is difficult to do so correctly, in
+        // part because there is no guarantee that the mangling will list the
+        // main trait first.  So we just print all the traits in their order of
+        // appearance in the mangled name.
+        dyn_trait_type:
+          if (!Emit("dyn ")) return false;
+          if (!ParseOptionalBinder()) return false;
+          if (!Eat('E')) {
+            ABSL_DEMANGLER_RECURSE(dyn_trait, kBeginAutoTraits);
+            while (!Eat('E')) {
+              if (!Emit(" + ")) return false;
+              ABSL_DEMANGLER_RECURSE(dyn_trait, kContinueAutoTraits);
+            }
+          }
+          if (!ParseRequiredLifetime()) return false;
+          continue;
+
+        // dyn-trait -> path dyn-trait-assoc-binding*
+        // dyn-trait-assoc-binding -> p undisambiguated-identifier type
+        //
+        // We render nonempty binding lists as <>, omitting their contents as
+        // for generic-args.
+        dyn_trait:
+          ABSL_DEMANGLER_RECURSE(path, kContinueDynTrait);
+          if (Peek() == 'p') {
+            if (!Emit("<>")) return false;
+            ++silence_depth_;
+            while (Eat('p')) {
+              if (!ParseUndisambiguatedIdentifier()) return false;
+              ABSL_DEMANGLER_RECURSE(type, kContinueAssocBinding);
+            }
+            --silence_depth_;
+          }
+          continue;
+
         // const -> type const-data | p | backref
         //
         // const is a C++ keyword, so we use the label `constant` instead.
@@ -477,6 +525,10 @@ class RustSymbolParser {
     kAfterSubsequentTupleElement,
     kContinueParameterList,
     kFinishFn,
+    kBeginAutoTraits,
+    kContinueAutoTraits,
+    kContinueDynTrait,
+    kContinueAssocBinding,
     kConstData,
     kBeginGenericArgList,
     kContinueGenericArgList,
@@ -750,6 +802,13 @@ class RustSymbolParser {
     return ParseBase62Number(ignored_de_bruijn_index);
   }
 
+  // Consumes a lifetime just like ParseOptionalLifetime, but returns false if
+  // there is no lifetime here.
+  ABSL_MUST_USE_RESULT bool ParseRequiredLifetime() {
+    if (Peek() != 'L') return false;
+    return ParseOptionalLifetime();
+  }
+
   // Pushes ns onto the namespace stack and returns true if the stack is not
   // full, else returns false.
   ABSL_MUST_USE_RESULT bool PushNamespace(char ns) {
diff --git a/absl/debugging/internal/demangle_rust_test.cc b/absl/debugging/internal/demangle_rust_test.cc
index 34b78134..00bba780 100644
--- a/absl/debugging/internal/demangle_rust_test.cc
+++ b/absl/debugging/internal/demangle_rust_test.cc
@@ -534,6 +534,50 @@ TEST(DemangleRust, LifetimeInGenericArgs) {
                     "c::f::<>");
 }
 
+TEST(DemangleRust, EmptyDynTrait) {
+  // This shouldn't happen, but the grammar allows it and existing demanglers
+  // accept it.
+  EXPECT_DEMANGLING("_RNvYDEL_NtC1c1t1f",
+                    "<dyn  as c::t>::f");
+}
+
+TEST(DemangleRust, SimpleDynTrait) {
+  EXPECT_DEMANGLING("_RNvYDNtC1c1tEL_NtC1d1u1f",
+                    "<dyn c::t as d::u>::f");
+}
+
+TEST(DemangleRust, DynTraitWithOneAssociatedType) {
+  EXPECT_DEMANGLING(
+      "_RNvYDNtC1c1tp1xlEL_NtC1d1u1f",  // <dyn c::t<x = i32> as d::u>::f
+      "<dyn c::t<> as d::u>::f");
+}
+
+TEST(DemangleRust, DynTraitWithTwoAssociatedTypes) {
+  EXPECT_DEMANGLING(
+      // <dyn c::t<x = i32, y = u32> as d::u>::f
+      "_RNvYDNtC1c1tp1xlp1ymEL_NtC1d1u1f",
+      "<dyn c::t<> as d::u>::f");
+}
+
+TEST(DemangleRust, DynTraitPlusAutoTrait) {
+  EXPECT_DEMANGLING(
+      "_RNvYDNtC1c1tNtNtC3std6marker4SendEL_NtC1d1u1f",
+      "<dyn c::t + std::marker::Send as d::u>::f");
+}
+
+TEST(DemangleRust, DynTraitPlusTwoAutoTraits) {
+  EXPECT_DEMANGLING(
+      "_RNvYDNtC1c1tNtNtC3std6marker4CopyNtBc_4SyncEL_NtC1d1u1f",
+      "<dyn c::t + std::marker::Copy + std::marker::Sync as d::u>::f");
+}
+
+TEST(DemangleRust, HigherRankedDynTrait) {
+  EXPECT_DEMANGLING(
+      // <dyn for<'a> c::t::<&'a i32> as d::u>::f
+      "_RNvYDG_INtC1c1tRL0_lEEL_NtC1d1u1f",
+      "<dyn c::t::<> as d::u>::f");
+}
+
 }  // namespace
 }  // namespace debugging_internal
 ABSL_NAMESPACE_END