Add Symbol coercion

The main use case for symbols is to use them as a HashMap key. However,
this introduces a GC problem – we cannot store Ruby values in the heap
without properly marking/registering them, otherwise they might get
GC'ed by Ruby unexpectedly. (In fact, this is already a problem if you
have a `Vec<VALUE>`.)

I tried to avoid introducing additional problems by pinning down any
symbols that goes thought the coercion protocol. This is probably
overly aggressive, as it would cause any dynamic symbols (e.g.
`String#to_sym`) to become un-GC-able. We can revisit this once we
have a more general-purpose system to encode pinning semantics in
the type system.

crates/libcruby-sys/src/lib.rs

@@ -22,7 +22,7 @@ pub type c_string = *const libc::c_char;
 // pub type c_func = extern "C" fn(...);
 
 #[repr(C)]
-#[derive(Copy, Clone, Debug)]
+#[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
 pub struct ID(*mut void);
 
 #[repr(C)]
@@ -30,7 +30,7 @@ pub struct ID(*mut void);
 pub struct VALUE(*mut void);
 
 #[repr(C)]
-#[derive(Copy, Clone, Eq, PartialEq, Debug)]
+#[derive(Eq, PartialEq, Copy, Clone, Debug)]
 pub struct RubyException(isize);
 
 impl RubyException {
@@ -163,6 +163,9 @@ extern "C" {
     #[link_name = "HELIX_T_FALSE"]
     pub static T_FALSE: isize;
 
+    #[link_name = "HELIX_T_SYMBOL"]
+    pub static T_SYMBOL: isize;
+
     #[link_name = "HELIX_T_FIXNUM"]
     pub static T_FIXNUM: isize;
 
@@ -188,6 +191,10 @@ extern "C" {
     pub fn rb_sprintf(specifier: c_string, ...) -> VALUE;
     pub fn rb_inspect(value: VALUE) -> VALUE;
     pub fn rb_intern(string: c_string) -> ID;
+    pub fn rb_intern_str(string: VALUE) -> ID;
+    pub fn rb_sym2id(symbol: VALUE) -> ID;
+    pub fn rb_id2sym(id: ID) -> VALUE;
+    pub fn rb_id2str(id: ID) -> VALUE;
     pub fn rb_ary_new_capa(capa: isize) -> VALUE;
     pub fn rb_ary_entry(ary: VALUE, offset: isize) -> VALUE;
     pub fn rb_ary_push(ary: VALUE, item: VALUE) -> VALUE;

examples/text_transform/spec/text_transform_spec.rb

@@ -11,13 +11,13 @@ describe "TextTransform" do
 
   it "can widen hash" do
     expect(TextTransform.widen_hash({
-      "message" => "Hello",
-      "name" => "Aaron",
-      "handle" => "@tenderlove"
+      message: "Hello",
+      name: "Aaron",
+      handle: "@tenderlove"
     })).to eq({
-      "ｍｅｓｓａｇｅ" => "Ｈｅｌｌｏ",
-      "ｎａｍｅ" => "Ａａｒｏｎ",
-      "ｈａｎｄｌｅ" => "＠ｔｅｎｄｅｒｌｏｖｅ"
+      "ｍｅｓｓａｇｅ": "Ｈｅｌｌｏ",
+      "ｎａｍｅ": "Ａａｒｏｎ",
+      "ｈａｎｄｌｅ": "＠ｔｅｎｄｅｒｌｏｖｅ"
     })
   end
 
@@ -31,13 +31,13 @@ describe "TextTransform" do
 
   it "can narrowen hash" do
     expect(TextTransform.narrowen_hash({
-      "ｍｅｓｓａｇｅ" => "Ｈｅｌｌｏ",
-      "ｎａｍｅ" => "Ａａｒｏｎ",
-      "ｈａｎｄｌｅ" => "＠ｔｅｎｄｅｒｌｏｖｅ"
+      "ｍｅｓｓａｇｅ": "Ｈｅｌｌｏ",
+      "ｎａｍｅ": "Ａａｒｏｎ",
+      "ｈａｎｄｌｅ": "＠ｔｅｎｄｅｒｌｏｖｅ"
     })).to eq({
-      "message" => "Hello",
-      "name" => "Aaron",
-      "handle" => "@tenderlove"
+      message: "Hello",
+      name: "Aaron",
+      handle: "@tenderlove"
     })
   end
 
@@ -51,13 +51,13 @@ describe "TextTransform" do
 
   it "can flip hash" do
     expect(TextTransform.flip_hash({
-      "message" => "Hello",
-      "name" => "Aaron",
-      "handle" => "@tenderlove"
+      message: "Hello",
+      name: "Aaron",
+      handle: "@tenderlove"
     })).to eq({
-      "ollǝH" => "ǝƃɐssǝɯ",
-      "uoɹɐ∀" => "ǝɯɐu",
-      "ǝʌolɹǝpuǝʇ@" => "ǝlpuɐɥ"
+      "ollǝH": "ǝƃɐssǝɯ",
+      "uoɹɐ∀": "ǝɯɐu",
+      "ǝʌolɹǝpuǝʇ@": "ǝlpuɐɥ"
     })
   end
 end

examples/text_transform/src/lib.rs

@@ -4,6 +4,7 @@
 extern crate helix;
 
 use std::collections::HashMap;
+use helix::Symbol;
 
 ruby! {
     class TextTransform {
@@ -30,8 +31,8 @@ ruby! {
             text.into_iter().map(TextTransform::widen).collect()
         }
 
-        def widen_hash(text: HashMap<String, String>) -> HashMap<String, String> {
-            text.into_iter().map(|(k,v)| (TextTransform::widen(k), TextTransform::widen(v))).collect()
+        def widen_hash(text: HashMap<Symbol, String>) -> HashMap<Symbol, String> {
+            text.into_iter().map(|(k,v)| (Symbol::from_string(TextTransform::widen(k.to_string())), TextTransform::widen(v))).collect()
         }
 
         def narrowen(text: String) -> String {
@@ -57,8 +58,8 @@ ruby! {
             text.into_iter().map(TextTransform::narrowen).collect()
         }
 
-        def narrowen_hash(text: HashMap<String, String>) -> HashMap<String, String> {
-            text.into_iter().map(|(k,v)| (TextTransform::narrowen(k), TextTransform::narrowen(v))).collect()
+        def narrowen_hash(text: HashMap<Symbol, String>) -> HashMap<Symbol, String> {
+            text.into_iter().map(|(k,v)| (Symbol::from_string(TextTransform::narrowen(k.to_string())), TextTransform::narrowen(v))).collect()
         }
 
         def flip(text: String) -> String {
@@ -83,8 +84,8 @@ ruby! {
             text.into_iter().rev().map(TextTransform::flip).collect()
         }
 
-        def flip_hash(text: HashMap<String, String>) -> HashMap<String, String> {
-            text.into_iter().map(|(k,v)| (TextTransform::flip(v), TextTransform::flip(k))).collect()
+        def flip_hash(text: HashMap<Symbol, String>) -> HashMap<Symbol, String> {
+            text.into_iter().map(|(k,v)| (Symbol::from_string(TextTransform::flip(v)), TextTransform::flip(k.to_string()))).collect()
         }
     }
 }

src/coercions/mod.rs

@@ -3,6 +3,7 @@ mod unit;
 mod bool;
 mod integers;
 mod float;
+mod symbol;
 mod string;
 mod option;
 mod result;

src/coercions/symbol.rs

@@ -0,0 +1,25 @@
+use sys::{VALUE, RB_TYPE_P, T_SYMBOL, rb_sym2id, rb_id2sym};
+use super::{FromRuby, CheckedValue, CheckResult, ToRuby, ToRubyResult};
+use super::super::{Symbol};
+
+impl FromRuby for Symbol {
+    type Checked = CheckedValue<Symbol>;
+
+    fn from_ruby(value: VALUE) -> CheckResult<CheckedValue<Symbol>> {
+        if unsafe { RB_TYPE_P(value, T_SYMBOL) } {
+            unsafe { Ok(CheckedValue::new(value)) }
+        } else {
+            type_error!(value, "a symbol")
+        }
+    }
+
+    fn from_checked(checked: CheckedValue<Symbol>) -> Symbol {
+        Symbol::from_id(unsafe { rb_sym2id(checked.to_value()) })
+    }
+}
+
+impl ToRuby for Symbol {
+    fn to_ruby(self) -> ToRubyResult {
+        Ok(unsafe { rb_id2sym(self.to_id()) })
+    }
+}

src/lib.rs

@@ -15,7 +15,7 @@ pub extern crate libcruby_sys as sys;
 // pub use rb;
 
 use std::ffi::CStr;
-use sys::VALUE;
+use sys::{VALUE, ID};
 
 #[macro_export]
 macro_rules! raise {
@@ -54,10 +54,39 @@ mod macros;
 pub use coercions::*;
 pub use errors::*;
 
+
+#[repr(C)]
+#[derive(Eq, PartialEq, Hash, Copy, Clone, Debug)]
+pub struct Symbol(ID);
+
+// Since the main use case for `Symbol` at the moment is as the
+// key for a `HashMap`, this tries to avoid GC issues by alaways
+// pinning the symbol, essentially making it a "copy type". This
+// is probably overly aggressive, we can reconsider this when we
+// have a more general-purpose mechanism to encode pinning
+// semantics in the type system.
+impl Symbol {
+    pub fn from_id(id: ID) -> Symbol {
+        Symbol(id)
+    }
+
+    pub fn to_id(self) -> ID {
+        self.0
+    }
+
+    pub fn from_string(string: String) -> Symbol {
+        Symbol(unsafe { sys::rb_intern_str(string.to_ruby().unwrap()) })
+    }
+
+    pub fn to_string(self) -> String {
+        unsafe { String::from_ruby_unwrap(sys::rb_id2str(self.0)) }
+    }
+}
+
 pub use class_definition::{ClassDefinition, MethodDefinition};
 
 #[repr(C)]
-#[derive(Copy, Clone, Debug)]
+#[derive(Eq, PartialEq, Copy, Clone, Debug)]
 pub struct Class(VALUE);
 
 pub trait RubyMethod {
@@ -101,7 +130,7 @@ impl Class {
         Class(value)
     }
 
-    pub fn to_value(&self) -> VALUE {
+    pub fn to_value(self) -> VALUE {
         self.0
     }