Recognize generic arguments containing only types in Rust mangled names.

We follow the C++ demangler in not printing the arguments, just an empty <>.

PiperOrigin-RevId: 635858791
Change-Id: I24903d4c5a1e2060e92ca950bf7a61647aee655f

absl/debugging/internal/demangle_rust.cc

@@ -154,7 +154,7 @@ class RustSymbolParser {
             case 'X': return false;  // trait-impl not yet implemented
             case 'Y': goto trait_definition;
             case 'N': goto nested_path;
-            case 'I': return false;  // generic-args not yet implemented
+            case 'I': goto generic_args;
             case 'B': goto path_backref;
             default: return false;
           }
@@ -290,6 +290,26 @@ class RustSymbolParser {
           --silence_depth_;
           continue;
 
+        // generic-args -> I path generic-arg* E (I already consumed)
+        //
+        // We follow the C++ demangler in omitting all the arguments from the
+        // output, printing only the list opening and closing tokens.
+        generic_args:
+          ABSL_DEMANGLER_RECURSE(path, kBeginGenericArgList);
+          if (!Emit("::<>")) return false;
+          ++silence_depth_;
+          while (!Eat('E')) {
+            ABSL_DEMANGLER_RECURSE(generic_arg, kContinueGenericArgList);
+          }
+          --silence_depth_;
+          continue;
+
+        // generic-arg -> lifetime | type | K const
+        generic_arg:
+          if (Eat('L')) return false;  // lifetime not yet implemented
+          if (Eat('K')) return false;  // const not yet implemented
+          goto type;
+
         // backref -> B base-62-number (B already consumed)
         //
         // The BeginBackref call parses and range-checks the base-62-number.  We
@@ -335,6 +355,8 @@ class RustSymbolParser {
     kAfterSecondTupleElement,
     kAfterThirdTupleElement,
     kAfterSubsequentTupleElement,
+    kBeginGenericArgList,
+    kContinueGenericArgList,
     kPathBackrefEnding,
     kTypeBackrefEnding,
   };

absl/debugging/internal/demangle_rust_test.cc

@@ -360,6 +360,45 @@ TEST(DemangleRust, ReturnFromBackrefToInputPosition256) {
                     " as c::t>::f");
 }
 
+TEST(DemangleRust, EmptyGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1fE", "c::f::<>");
+}
+
+TEST(DemangleRust, OneSimpleTypeInGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1flE",  // c::f::<i32>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, OneTupleInGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1fTlmEE",  // c::f::<(i32, u32)>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, OnePathInGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1fNtC1d1sE",  // c::f::<d::s>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, LongerGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1flmRNtC1d1sE",  // c::f::<i32, u32, &d::s>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, BackrefInGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1fRlB7_NtB2_1sE",  // c::f::<&i32, &i32, c::s>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, NestedGenericArgs) {
+  EXPECT_DEMANGLING("_RINvC1c1fINtB2_1slEmE",  // c::f::<c::s::<i32>, u32>
+                    "c::f::<>");
+}
+
+TEST(DemangleRust, MonomorphicEntityNestedInsideGeneric) {
+  EXPECT_DEMANGLING("_RNvINvC1c1fppE1g",  // c::f::<_, _>::g
+                    "c::f::<>::g");
+}
+
 }  // namespace
 }  // namespace debugging_internal
 ABSL_NAMESPACE_END