Rollup merge of #79184 - nanguye2496:nanguye2496/fix_slice_and_str_type_name, r=varkor

Stop adding '*' at the end of slice and str typenames for MSVC case

When computing debug info for MSVC debuggers, Rust compiler emits C++ style type names for compatibility with .natvis visualizers. All Ref types are treated as equivalences of C++ pointers in this process, and, as a result, their type names end with a '\*'. Since Slice and Str are treated as Ref by the compiler, their type names also end with a '\*'. This causes the .natvis engine for WinDbg fails to display data of Slice and Str objects. We addressed this problem simply by removing the '*' at the end of type names for Slice and Str types.

Debug info in WinDbg before the fix:
![image](https://user-images.githubusercontent.com/74681961/99594120-9a4dcf80-29a7-11eb-8cce-aedaf1da6d21.png)

Debug info in WinDbg after the fix:
![image](https://user-images.githubusercontent.com/74681961/99597173-717c0900-29ac-11eb-861e-98143a9177cf.png)

This change has also been tested with debuggers for Visual Studio, VS Code C++ and VS Code LLDB to make sure that it does not affect the behavior of other kinds of debugger.

Author: m-ou-se

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -94,7 +94,14 @@ pub fn push_debuginfo_type_name<'tcx>(
             push_debuginfo_type_name(tcx, inner_type, true, output, visited);
 
             if cpp_like_names {
-                output.push('*');
+                // Slices and `&str` are treated like C++ pointers when computing debug
+                // info for MSVC debugger. However, adding '*' at the end of these types' names
+                // causes the .natvis engine for WinDbg to fail to display their data, so we opt these
+                // types out to aid debugging in MSVC.
+                match *inner_type.kind() {
+                    ty::Slice(_) | ty::Str => {}
+                    _ => output.push('*'),
+                }
             }
         }
         ty::Array(inner_type, len) => {