Implements Debug trait for types which do not support derive Debug

For types that do not support derive Debug be implemented automatically by rust,
we know can generate implementations of the Debug trait. This code generation is
hidden behind the '--force-derive-debug' command-line flag.

src/codegen/derive_debug.rs

@@ -0,0 +1,197 @@
+use ir::comp::{BitfieldUnit, CompKind, Field, FieldData, FieldMethods};
+use ir::context::BindgenContext;
+use ir::derive::CanTriviallyDeriveDebug;
+use ir::item::{IsOpaque, Item, ItemCanonicalName};
+use ir::ty::{TypeKind, RUST_DERIVE_IN_ARRAY_LIMIT};
+use syntax::ast;
+use syntax::codemap::DUMMY_SP;
+use syntax::parse::token::Token;
+
+use syntax::tokenstream::TokenTree;
+
+pub fn gen_debug_impl(
+    ctx: &BindgenContext,
+    fields: &[Field],
+    item: &Item,
+    kind: CompKind,
+) -> Vec<ast::ImplItem> {
+    let struct_name = item.canonical_name(ctx);
+    let mut format_string = format!("{} {{{{ ", struct_name);
+    let mut tokens: Vec<TokenTree> = Vec::new();
+
+    if item.is_opaque(ctx, &()) {
+        format_string.push_str("opaque");
+    } else {
+        match kind {
+            CompKind::Union => {
+                format_string.push_str("union");
+            }
+            CompKind::Struct => {
+                let processed_fields = fields.iter().filter_map(|f| match f {
+                    &Field::DataMember(ref fd) => {
+                        gen_field_data_debug_impl(ctx, fd)
+                    }
+                    &Field::Bitfields(ref bu) => {
+                        gen_bitfield_unit_debug_impl(ctx, bu)
+                    }
+                });
+
+
+                for (i, (fstring, token)) in processed_fields.enumerate() {
+                    if i > 0 {
+                        format_string.push_str(", ");
+                    }
+                    if !token.is_empty() {
+                        tokens.push(TokenTree::Token(DUMMY_SP, Token::Comma));
+                        tokens.extend(token);
+                    }
+                    format_string.push_str(&fstring);
+                }
+            }
+        }
+    }
+
+    format_string.push_str(" }}");
+
+    let impl_ = quote_item!(ctx.ext_cx(),
+                            impl X {
+                                fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+                                    write!(f, $format_string $tokens)
+                                }    
+                            });
+
+    match impl_.unwrap().node {
+        ast::ItemKind::Impl(_, _, _, _, _, ref items) => items.clone(),
+        _ => unreachable!(),
+    }
+}
+
+fn gen_field_data_debug_impl(
+    ctx: &BindgenContext,
+    data: &FieldData,
+) -> Option<(String, Vec<TokenTree>)> {
+    if let Some(name) = data.name() {
+        gen_item_debug_impl(ctx, ctx.resolve_item(data.ty()), name)
+    } else {
+        None
+    }
+}
+
+fn gen_bitfield_unit_debug_impl(
+    ctx: &BindgenContext,
+    data: &BitfieldUnit,
+) -> Option<(String, Vec<TokenTree>)> {
+    let mut format_string = String::new();
+    let mut tokens = Vec::new();
+    for (i, bu) in data.bitfields().iter().enumerate() {
+        if i > 0 {
+            format_string.push_str(", ");
+            tokens.push(TokenTree::Token(DUMMY_SP, Token::Comma));
+        }
+        format_string.push_str(&format!("{} : {{:?}}", bu.name()));
+        let name_ident = ctx.rust_ident_raw(bu.name());
+        tokens.extend(quote_tokens!(ctx.ext_cx(), self.$name_ident()));
+    }
+
+    Some((format_string, tokens))
+}
+
+fn gen_item_debug_impl(
+    ctx: &BindgenContext,
+    item: &Item,
+    name: &str,
+) -> Option<(String, Vec<TokenTree>)> {
+    let name_ident = ctx.rust_ident_raw(name);
+
+    let ty = match item.as_type() {
+        Some(ty) => ty,
+        None => {
+            return None;
+        }
+    };
+
+    fn debug_print(
+        ctx: &BindgenContext,
+        name: &str,
+        name_ident: ast::Ident,
+    ) -> Option<(String, Vec<TokenTree>)> {
+        Some((
+            format!("{}: {{:?}}", name),
+            quote_tokens!(ctx.ext_cx(), self.$name_ident),
+        ))
+    }
+
+    match *ty.kind() {
+        // Handle the simple cases.
+        TypeKind::Void |
+        TypeKind::NullPtr |
+        TypeKind::Int(..) |
+        TypeKind::Float(..) |
+        TypeKind::Complex(..) |
+        TypeKind::Function(..) |
+        TypeKind::Enum(..) |
+        TypeKind::Reference(..) |
+        TypeKind::BlockPointer |
+        TypeKind::UnresolvedTypeRef(..) |
+        TypeKind::ObjCInterface(..) |
+        TypeKind::ObjCId |
+        TypeKind::Comp(..) |
+        TypeKind::ObjCSel => debug_print(ctx, name, name_ident),
+
+        TypeKind::TemplateInstantiation(ref inst) => {
+            if inst.is_opaque(ctx, item) {
+                Some((format!("{}: opaque", name), vec![]))
+            } else {
+                debug_print(ctx, name, name_ident)
+            }
+        } 
+
+        // The generic is not required to implement Debug, so we can not debug print that type
+        TypeKind::Named => {
+            Some((format!("{}: Non-debuggable generic", name), vec![]))
+        }
+
+        TypeKind::Array(_, len) => {
+            // Generics are not required to implement Debug
+            if ctx.lookup_item_id_has_type_param_in_array(&item.id()) {
+                Some((format!("{}: Array with length {}", name, len), vec![]))
+            } else if len < RUST_DERIVE_IN_ARRAY_LIMIT {
+                // The simple case
+                debug_print(ctx, name, name_ident)
+            } else {
+                // Let's implement our own print function
+                Some((
+                    format!("{}: [{{}}]", name),
+                    quote_tokens!(
+                        ctx.ext_cx(),
+                        self.$name_ident
+                            .iter()
+                            .enumerate()
+                            .map(|(i, v)| format!("{}{:?}", if i > 0 { ", " } else { "" }, v))
+                            .collect::<String>()),
+                ))
+            }
+        }
+
+        TypeKind::ResolvedTypeRef(t) |
+        TypeKind::TemplateAlias(t, _) |
+        TypeKind::Alias(t) => {
+            // We follow the aliases
+            gen_item_debug_impl(ctx, ctx.resolve_item(t), name)
+        }
+
+        TypeKind::Pointer(inner) => {
+            let inner_type = ctx.resolve_type(inner).canonical_type(ctx);
+            match *inner_type.kind() {
+                TypeKind::Function(ref sig)
+                    if !sig.can_trivially_derive_debug() =>
+                {
+                    Some((format!("{}: FunctionPointer", name), vec![]))
+                }
+                _ => debug_print(ctx, name, name_ident),
+            }
+        }
+
+        TypeKind::Opaque => None,
+    }
+}