[Demangle][Rust] Parse tuples

[tmiasko]

Summary

Depends on D102578

[dblaikie]

llvm/lib/Demangle/RustDemangle.cpp

452–453

Looks a bit awkward to print a comma after a single argument ((_,)) - is that necessary? (does it disambiguate this with some other case that has only a list of 1 between parentheses?)

[tmiasko]

llvm/lib/Demangle/RustDemangle.cpp

452–453

The intention is to match Rust language syntax which requires a comma after one element tuples to disambiguate them from parenthesized types.

[dblaikie]

llvm/lib/Demangle/RustDemangle.cpp

452–453

Cool - thanks for the context!

And stylistically, that trailing comma is usually written without a space after it, unlike separating commas?

Pity, this could come out more naturally from the algorithm if that was the case (always printing ", " after every type - rather than having to special case)

I guess you could do it this way:

for (...) {
  if (I > 0)
    print(" ");
  demangleType();
  print(",");
}

Marginally less special casing

[tmiasko]

Rebase

llvm/lib/Demangle/RustDemangle.cpp

452–453

Looking at rustfmt, rustc type printer and other demanglers, they are consistent writing trailing comma without a space. They also include the trailing comma only when necessary, i.e., for one element tuple only (so I retained the special case).

[dblaikie]

llvm/lib/Demangle/RustDemangle.cpp

452–453

Cool, I still wonder if it might be marginally more neatly written the way I suggested - it still produces the same output, but with one fewer "if", I think?

[tmiasko]

llvm/lib/Demangle/RustDemangle.cpp

452–453

It would be (), (T1,), and then (T1, T2,) instead of (T1, T2).

[dblaikie]

llvm/lib/Demangle/RustDemangle.cpp

452–453

Oh, right. Thanks for setting me straight!

llvm/lib/Demangle/RustDemangle.cpp

case 'A':
     demangleConst();
     print("]");
     break;
   case 'S':
     print("[");
     demangleType();
     print("]");
     break;
+  case 'T': {
+    print("(");
+    size_t I = 0;
+    for (; !Error && !consumeIf('E'); ++I) {
+      if (I > 0)
+        print(", ");
+      demangleType();
+    }
+    if (I == 1)
+      print(",");
+    print(")");
+    break;
+  }
   default:
     Position = Start;
     demanglePath(InType::Yes);
     break;
   }
 }
 
 // <const> = <basic-type> <const-data>

llvm/test/Demangle/rust.test

 ; Types
 
 CHECK: types::<[u8; 0]>
        _RIC5typesAhj0_E
 
 CHECK: types::<[_]>
        _RIC5typesSpE
 
+CHECK: types::<()>
+       _RIC5typesTEE
+
+CHECK: types::<(_,)>
+       _RIC5typesTpEE
+
+CHECK: types::<(_, _)>
+       _RIC5typesTppEE
+
+CHECK: types::<(_, _, _)>
+       _RIC5typesTpppEE
+
 ; Integer constants. Test value demangling.
 
 CHECK: integer::<0>
        _RIC7integerKi0_E
 
 CHECK: integer::<1>
        _RIC7integerKi1_E