Address some review feedback

Author: alexcrichton

phases/ephemeral/docs.md

@@ -1,5 +1,5 @@
 # Types
-## <a href="#size" name="size"></a> `size`: `u32`
+## <a href="#size" name="size"></a> `size`: `usize`
 An array size.
 
 Note: This is similar to `size_t` in POSIX.

tools/witx/src/ast.rs

@@ -211,13 +211,19 @@ impl Type {
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum BuiltinType {
+    /// This is a 32-bit unicode scalar value, not a code point.
+    ///
+    /// Same as the Rust language's `char` type.
     Char,
     U8 {
         /// Indicates whether this type is intended to represent the `char`
         /// type in the C language. The C `char` type is often unsigned, but
         /// it's language-specific. At an interface-types level this is an
         /// unsigned byte but binding generators may wish to bind this as the
         /// language-specific representation for a C character instead.
+        ///
+        /// This is also currently used exclusively in conjunction with `@witx
+        /// pointer` to hint that it's pointing to unicode string data as well.
         lang_c_char: bool,
     },
     U16,

tools/witx/src/docs/ast.rs

@@ -291,7 +291,12 @@ impl BuiltinType {
             BuiltinType::Char => "char",
             BuiltinType::U8 { .. } => "u8",
             BuiltinType::U16 => "u16",
-            BuiltinType::U32 { .. } => "u32",
+            BuiltinType::U32 {
+                lang_ptr_size: false,
+            } => "u32",
+            BuiltinType::U32 {
+                lang_ptr_size: true,
+            } => "usize",
             BuiltinType::U64 => "u64",
             BuiltinType::S8 => "s8",
             BuiltinType::S16 => "s16",