Improvements to NatVis support

NatVis files describe how to display types in some Windows debuggers,
such as Visual Studio, WinDbg, and VS Code.

This commit makes several improvements:

* Adds visualizers for Rc<T>, Weak<T>, and Arc<T>.

* Changes [size] to [len], for consistency with the Rust API.
  Visualizers often use [size] to mirror the size() method on C++ STL
  collections.

* Several visualizers used the PVOID and ULONG typedefs. These are part
  of the Windows API; they are not guaranteed to always be defined in a
  pure Rust DLL/EXE. I converted PVOID to `void*` and `ULONG` to
  `unsigned long`.

* Cosmetic change: Removed {} braces around the visualized display
  for `Option` types. They now display simply as `Some(value)` or
  `None`, which reflects what is written in source code.

* The visualizer for `alloc::string::String` makes assumptions about
  the layout of `String` (it casts `String*` to another type), rather
  than using symbolic expressions. This commit changes the visualizer
  so that it simply uses symbolic expressions to access the string
  data and string length.

src/etc/natvis/intrinsic.natvis

@@ -4,17 +4,21 @@
     <DisplayString>{data_ptr,[length]s8}</DisplayString>
     <StringView>data_ptr,[length]s8</StringView>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">length</Item>
-      <ArrayItems>
-        <Size>length</Size>
-        <ValuePointer>data_ptr</ValuePointer>
-      </ArrayItems>
+      <Item Name="[len]" ExcludeView="simple">length</Item>
+      <Synthetic Name="[chars]">
+        <Expand>
+          <ArrayItems>
+            <Size>length</Size>
+            <ValuePointer>data_ptr</ValuePointer>
+          </ArrayItems>
+        </Expand>
+      </Synthetic>
     </Expand>
   </Type>
   <Type Name="slice&lt;*&gt;">
-    <DisplayString>{{ length={length} }}</DisplayString>
+    <DisplayString>{{ len={length} }}</DisplayString>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">length</Item>
+      <Item Name="[len]" ExcludeView="simple">length</Item>
       <ArrayItems>
         <Size>length</Size>
         <ValuePointer>data_ptr</ValuePointer>

src/etc/natvis/liballoc.natvis

@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
   <Type Name="alloc::vec::Vec&lt;*&gt;">
-    <DisplayString>{{ size={len} }}</DisplayString>
+    <DisplayString>{{ len={len} }}</DisplayString>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">len</Item>
+      <Item Name="[len]" ExcludeView="simple">len</Item>
       <Item Name="[capacity]" ExcludeView="simple">buf.cap</Item>
       <ArrayItems>
         <Size>len</Size>
@@ -12,9 +12,9 @@
     </Expand>
   </Type>
   <Type Name="alloc::collections::vec_deque::VecDeque&lt;*&gt;">
-    <DisplayString>{{ size={tail &lt;= head ? head - tail : buf.cap - tail + head} }}</DisplayString>
+    <DisplayString>{{ len={tail &lt;= head ? head - tail : buf.cap - tail + head} }}</DisplayString>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">tail &lt;= head ? head - tail : buf.cap - tail + head</Item>
+      <Item Name="[len]" ExcludeView="simple">tail &lt;= head ? head - tail : buf.cap - tail + head</Item>
       <Item Name="[capacity]" ExcludeView="simple">buf.cap</Item>
       <CustomListItems>
         <Variable Name="i" InitialValue="tail" />
@@ -31,7 +31,7 @@
     </Expand>
   </Type>
   <Type Name="alloc::collections::linked_list::LinkedList&lt;*&gt;">
-    <DisplayString>{{ size={len} }}</DisplayString>
+    <DisplayString>{{ len={len} }}</DisplayString>
     <Expand>
       <LinkedListItems>
         <Size>len</Size>
@@ -42,15 +42,37 @@
     </Expand>
   </Type>
   <Type Name="alloc::string::String">
-    <DisplayString>{*(char**)this,[vec.len]s8}</DisplayString>
-    <StringView>*(char**)this,[vec.len]s8</StringView>
+    <DisplayString>{(char*)vec.buf.ptr.pointer,[vec.len]s8}</DisplayString>
+    <StringView>(char*)vec.buf.ptr.pointer,[vec.len]s8</StringView>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">vec.len</Item>
+      <Item Name="[len]" ExcludeView="simple">vec.len</Item>
       <Item Name="[capacity]" ExcludeView="simple">vec.buf.cap</Item>
-      <ArrayItems>
-        <Size>vec.len</Size>
-        <ValuePointer>*(char**)this</ValuePointer>
-      </ArrayItems>
+      <Synthetic Name="[chars]">
+        <Expand>
+          <ArrayItems>
+            <Size>vec.len</Size>
+            <ValuePointer>(char*)vec.buf.ptr.pointer</ValuePointer>
+          </ArrayItems>
+        </Expand>
+      </Synthetic>
+    </Expand>
+  </Type>
+  <Type Name="alloc::rc::Rc&lt;*&gt;">
+    <DisplayString>{ptr.pointer->value}</DisplayString>
+    <Expand>
+      <ExpandedItem>ptr.pointer->value</ExpandedItem>
+    </Expand>
+  </Type>
+  <Type Name="alloc::sync::Arc&lt;*&gt;">
+    <DisplayString>{ptr.pointer->data}</DisplayString>
+    <Expand>
+      <ExpandedItem>ptr.pointer->data</ExpandedItem>
+    </Expand>
+  </Type>
+  <Type Name="alloc::sync::Weak&lt;*&gt;">
+    <DisplayString>{ptr.pointer->data}</DisplayString>
+    <Expand>
+      <ExpandedItem>ptr.pointer->data</ExpandedItem>
     </Expand>
   </Type>
 </AutoVisualizer>

src/etc/natvis/libcore.natvis

@@ -6,34 +6,28 @@
       <Item Name="[ptr]">pointer</Item>
     </Expand>
   </Type>
+
   <Type Name="core::ptr::Shared&lt;*&gt;">
     <DisplayString>{{ Shared {pointer} }}</DisplayString>
     <Expand>
       <Item Name="[ptr]">pointer</Item>
     </Expand>
   </Type>
+
   <Type Name="core::option::Option&lt;*&gt;">
-    <DisplayString Condition="RUST$ENUM$DISR == 0x0">{{ None }}</DisplayString>
-    <DisplayString Condition="RUST$ENUM$DISR == 0x1">{{ Some {__0} }}</DisplayString>
+    <DisplayString Condition="RUST$ENUM$DISR == 0x0">None</DisplayString>
+    <DisplayString Condition="RUST$ENUM$DISR == 0x1">Some({__0})</DisplayString>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">(ULONG)(RUST$ENUM$DISR != 0)</Item>
-      <Item Name="[value]" ExcludeView="simple">__0</Item>
-      <ArrayItems>
-        <Size>(ULONG)(RUST$ENUM$DISR != 0)</Size>
-        <ValuePointer>&amp;__0</ValuePointer>
-      </ArrayItems>
+      <Item Name="[value]" ExcludeView="simple" Condition="RUST$ENUM$DISR == 1">__0</Item>
     </Expand>
   </Type>
+
   <Type Name="core::option::Option&lt;*&gt;" Priority="MediumLow">
-    <DisplayString Condition="*(PVOID *)this == nullptr">{{ None }}</DisplayString>
-    <DisplayString>{{ Some {($T1 *)this} }}</DisplayString>
+    <DisplayString Condition="*(void**)this == nullptr">None</DisplayString>
+    <DisplayString>Some({($T1 *)this})</DisplayString>
     <Expand>
-      <Item Name="[size]" ExcludeView="simple">(ULONG)(*(PVOID *)this != nullptr)</Item>
-      <Item Name="[value]" ExcludeView="simple" Condition="*(PVOID *)this != nullptr">($T1 *)this</Item>
-      <ArrayItems>
-        <Size>(ULONG)(*(PVOID *)this != nullptr)</Size>
-        <ValuePointer>($T1 *)this</ValuePointer>
-      </ArrayItems>
+      <Item Name="Some" ExcludeView="simple" Condition="*(void**)this != nullptr">($T1 *)this</Item>
     </Expand>
   </Type>
+
 </AutoVisualizer>

src/etc/natvis/libstd.natvis

@@ -26,9 +26,9 @@
   -->
 
   <Type Name="std::collections::hash::map::HashMap&lt;*,*,*&gt;">
-    <DisplayString>{{ size={base.table.items} }}</DisplayString>
+    <DisplayString>{{ len={base.table.items} }}</DisplayString>
     <Expand>
-      <Item Name="[size]">base.table.items</Item>
+      <Item Name="[len]">base.table.items</Item>
       <Item Name="[capacity]">base.table.items + base.table.growth_left</Item>
       <Item Name="[state]">base.hash_builder</Item>
 
@@ -50,9 +50,9 @@
   </Type>
 
   <Type Name="std::collections::hash::set::HashSet&lt;*,*&gt;">
-    <DisplayString>{{ size={base.map.table.items} }}</DisplayString>
+    <DisplayString>{{ len={base.map.table.items} }}</DisplayString>
     <Expand>
-      <Item Name="[size]">base.map.table.items</Item>
+      <Item Name="[len]">base.map.table.items</Item>
       <Item Name="[capacity]">base.map.table.items + base.map.table.growth_left</Item>
       <Item Name="[state]">base.map.hash_builder</Item>