Start removal of vector special-casing

This commit starts wasm-bindgen down a path of removing the special
casing it currently has around vectors, slices, and strings. This has
long been a thorn in wasm-bindgen's side as it doesn't handle other
kinds of vectors and otherwise is very inflexible with future additions.
Additionally it leads to a lot of duplicated-ish code throughout various
portions of codegen.

The fundamental reason for this was that two arguments were required to
be passed back to wasm, and I couldn't figure out a way to shove both
those arguments into a function argument. The new strategy here is that
there is one global stack well known to both JS and Rust which arguments
*may* also be transferred between.

By default all ABI arguments pass as literal function arguments, but if
two or more arguments need to be passed then the extra ones are all
passed through this global stack. The stack is effectively temporary
scratch space when crossing the JS/Rust boundary (both ways). No long
term storage is intended here.

The `simple` test is passing as a result of this commit, using strings
internally. The `Vector` type in the AST has been removed (yay!) and the
bulk of the implementation of slices and vectors now resides in the
`wasm-bindgen` crate itself, defining how to pass all these arguments
around. The JS generator, however, still needs to know about all the
sorts of vectors so it can generate appropriate code for JS.

Future commits will continue cleanup and get the rest of the tests
working.

crates/shared/src/lib.rs

@@ -85,7 +85,7 @@ pub struct Function {
 
 #[derive(Deserialize)]
 pub struct CustomTypeName {
-    pub descriptor: char,
+    pub descriptor: u32,
     pub name: String,
 }
 
@@ -112,51 +112,42 @@ pub fn struct_function_export_name(struct_: &str, f: &str) -> String {
     return name
 }
 
-pub type Type = char;
+pub type Type = u32;
 
-pub const TYPE_VECTOR_JSVALUE: char = '\u{5b}';
-// Note: '\u{5c}' is '\' which breaks json encoding/decoding
-pub const TYPE_ENUM: char = '\u{5d}';
-pub const TYPE_NUMBER: char = '\u{5e}';
-pub const TYPE_BORROWED_STR: char = '\u{5f}';
-pub const TYPE_STRING: char = '\u{60}';
-pub const TYPE_BOOLEAN: char = '\u{61}';
-pub const TYPE_SLICE_U8: char = '\u{62}';
-pub const TYPE_VECTOR_U8: char = '\u{63}';
-pub const TYPE_SLICE_I8: char = '\u{64}';
-pub const TYPE_VECTOR_I8: char = '\u{65}';
-pub const TYPE_SLICE_U16: char = '\u{66}';
-pub const TYPE_VECTOR_U16: char = '\u{67}';
-pub const TYPE_SLICE_I16: char = '\u{68}';
-pub const TYPE_VECTOR_I16: char = '\u{69}';
-pub const TYPE_SLICE_U32: char = '\u{6a}';
-pub const TYPE_VECTOR_U32: char = '\u{6b}';
-pub const TYPE_SLICE_I32: char = '\u{6c}';
-pub const TYPE_VECTOR_I32: char = '\u{6d}';
-pub const TYPE_VECTOR_F32: char = '\u{6e}';
-pub const TYPE_SLICE_F32: char = '\u{6f}';
-pub const TYPE_VECTOR_F64: char = '\u{70}';
-pub const TYPE_SLICE_F64: char = '\u{71}';
-pub const TYPE_JS_OWNED: char = '\u{72}';
-pub const TYPE_JS_REF: char = '\u{73}';
+pub const TYPE_VECTOR_JSVALUE: u32 = 0;
+pub const TYPE_ENUM: u32 = 1;
+pub const TYPE_NUMBER: u32 = 2;
+pub const TYPE_BORROWED_STR: u32 = 3;
+pub const TYPE_STRING: u32 = 4;
+pub const TYPE_BOOLEAN: u32 = 5;
+pub const TYPE_SLICE_U8: u32 = 6;
+pub const TYPE_VECTOR_U8: u32 = 7;
+pub const TYPE_SLICE_I8: u32 = 8;
+pub const TYPE_VECTOR_I8: u32 = 9;
+pub const TYPE_SLICE_U16: u32 = 10;
+pub const TYPE_VECTOR_U16: u32 = 11;
+pub const TYPE_SLICE_I16: u32 = 12;
+pub const TYPE_VECTOR_I16: u32 = 13;
+pub const TYPE_SLICE_U32: u32 = 14;
+pub const TYPE_VECTOR_U32: u32 = 15;
+pub const TYPE_SLICE_I32: u32 = 16;
+pub const TYPE_VECTOR_I32: u32 = 17;
+pub const TYPE_VECTOR_F32: u32 = 18;
+pub const TYPE_SLICE_F32: u32 = 19;
+pub const TYPE_VECTOR_F64: u32 = 20;
+pub const TYPE_SLICE_F64: u32 = 21;
+pub const TYPE_JS_OWNED: u32 = 22;
+pub const TYPE_JS_REF: u32 = 23;
 
-pub const TYPE_CUSTOM_START: u32 = 0x74;
+pub const TYPE_CUSTOM_START: u32 = 24;
 pub const TYPE_CUSTOM_REF_FLAG: u32 = 1;
 
-pub fn name_to_descriptor(name: &str) -> char {
-    const CHAR_MAX: u32 = 0x10ffff;
-    const CHAR_HOLE_START: u32 = 0xd800;
-    const CHAR_HOLE_END: u32 = 0xe000;
+pub fn name_to_descriptor(name: &str) -> u32 {
+    const MAX: u32 = 10_000;
     let mut h = fnv::FnvHasher::default();
     name.hash(&mut h);
-    let val = h.finish();
-    let range = (CHAR_MAX - (CHAR_HOLE_END - CHAR_HOLE_START) - TYPE_CUSTOM_START) / 2;
-    let idx = (val % (range as u64)) as u32;
-    let mut ret = TYPE_CUSTOM_START + idx * 2;
-    if CHAR_HOLE_START <= ret && ret < CHAR_HOLE_END {
-        ret += CHAR_HOLE_END - CHAR_HOLE_START;
-    }
-    char::from_u32(ret).unwrap()
+    ((h.finish() as u32) % (MAX - TYPE_CUSTOM_START)) + TYPE_CUSTOM_START
+
 }
 
 pub fn version() -> String {