diff --git a/contrib/codegen/Cargo.toml b/contrib/codegen/Cargo.toml
index b2f07c03..94b90703 100644
--- a/contrib/codegen/Cargo.toml
+++ b/contrib/codegen/Cargo.toml
@@ -20,7 +20,7 @@ proc-macro = true
 
 [dependencies]
 quote = "1.0"
-devise = { git = "https://github.com/SergioBenitez/Devise.git", rev = "e58b3ac9a" }
+devise = { git = "https://github.com/SergioBenitez/Devise.git", rev = "57d6eb80" }
 
 [build-dependencies]
 yansi = "0.5"
diff --git a/contrib/codegen/src/database.rs b/contrib/codegen/src/database.rs
index 2fea4263..6cad8adc 100644
--- a/contrib/codegen/src/database.rs
+++ b/contrib/codegen/src/database.rs
@@ -1,5 +1,6 @@
 use proc_macro::TokenStream;
-use devise::{Spanned, Result};
+use devise::{Spanned, Result, ext::SpanDiagnosticExt};
+
 use crate::syn::{DataStruct, Fields, Data, Type, LitStr, DeriveInput, Ident, Visibility};
 
 #[derive(Debug)]
diff --git a/contrib/codegen/src/lib.rs b/contrib/codegen/src/lib.rs
index e45cefc9..b32a9b11 100644
--- a/contrib/codegen/src/lib.rs
+++ b/contrib/codegen/src/lib.rs
@@ -1,4 +1,3 @@
-#![feature(proc_macro_diagnostic)]
 #![recursion_limit="256"]
 
 #![warn(rust_2018_idioms)]
@@ -42,8 +41,6 @@ use proc_macro::TokenStream;
 #[cfg(feature = "database_attribute")]
 #[proc_macro_attribute]
 pub fn database(attr: TokenStream, input: TokenStream) -> TokenStream {
-    crate::database::database_attr(attr, input).unwrap_or_else(|diag| {
-        diag.emit();
-        TokenStream::new()
-    })
+    crate::database::database_attr(attr, input)
+        .unwrap_or_else(|diag| diag.emit_as_tokens().into())
 }
diff --git a/core/codegen/Cargo.toml b/core/codegen/Cargo.toml
index e3d70c20..3bb3385a 100644
--- a/core/codegen/Cargo.toml
+++ b/core/codegen/Cargo.toml
@@ -19,7 +19,7 @@ proc-macro = true
 indexmap = "1.0"
 quote = "1.0"
 rocket_http = { version = "0.5.0-dev", path = "../http/" }
-devise = { git = "https://github.com/SergioBenitez/Devise.git", rev = "e58b3ac9a" }
+devise = { git = "https://github.com/SergioBenitez/Devise.git", rev = "17f647e" }
 glob = "0.3"
 
 [build-dependencies]
diff --git a/core/codegen/src/attribute/async_entry.rs b/core/codegen/src/attribute/async_entry.rs
index edb1f367..c6c75625 100644
--- a/core/codegen/src/attribute/async_entry.rs
+++ b/core/codegen/src/attribute/async_entry.rs
@@ -1,15 +1,13 @@
-use proc_macro::{TokenStream, Span};
-use devise::{syn, Spanned, Result};
-
-use crate::proc_macro2::TokenStream as TokenStream2;
-use crate::syn_ext::syn_to_diag;
+use devise::{syn, Diagnostic, Spanned, Result};
+use devise::ext::SpanDiagnosticExt;
+use devise::proc_macro2::{TokenStream, Span};
 
 trait EntryAttr {
     /// Whether the attribute requires the attributed function to be `async`.
     const REQUIRES_ASYNC: bool;
 
     /// Return a new or rewritten function, using block as the main execution.
-    fn function(f: &syn::ItemFn, body: &syn::Block) -> Result<TokenStream2>;
+    fn function(f: &syn::ItemFn, body: &syn::Block) -> Result<TokenStream>;
 }
 
 struct Main;
@@ -17,13 +15,12 @@ struct Main;
 impl EntryAttr for Main {
     const REQUIRES_ASYNC: bool = true;
 
-    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream2> {
+    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream> {
         let (attrs, vis, mut sig) = (&f.attrs, &f.vis, f.sig.clone());
         if sig.ident != "main" {
-            Span::call_site()
+            return Err(Span::call_site()
                 .warning("attribute is typically applied to `main` function")
-                .span_note(sig.span(), "this function is not `main`")
-                .emit();
+                .span_note(sig.span(), "this function is not `main`"));
         }
 
         sig.asyncness = None;
@@ -38,7 +35,7 @@ struct Test;
 impl EntryAttr for Test {
     const REQUIRES_ASYNC: bool = true;
 
-    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream2> {
+    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream> {
         let (attrs, vis, mut sig) = (&f.attrs, &f.vis, f.sig.clone());
         sig.asyncness = None;
         Ok(quote_spanned!(block.span().into() => #(#attrs)* #[test] #vis #sig {
@@ -52,7 +49,7 @@ struct Launch;
 impl EntryAttr for Launch {
     const REQUIRES_ASYNC: bool = false;
 
-    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream2> {
+    fn function(f: &syn::ItemFn, block: &syn::Block) -> Result<TokenStream> {
         if f.sig.ident == "main" {
             return Err(Span::call_site()
                 .error("attribute cannot be applied to `main` function")
@@ -89,9 +86,9 @@ impl EntryAttr for Launch {
     }
 }
 
-fn parse_input<A: EntryAttr>(input: TokenStream) -> Result<syn::ItemFn> {
+fn parse_input<A: EntryAttr>(input: proc_macro::TokenStream) -> Result<syn::ItemFn> {
     let function: syn::ItemFn = syn::parse(input)
-        .map_err(syn_to_diag)
+        .map_err(Diagnostic::from)
         .map_err(|d| d.help("attribute can only be applied to functions"))?;
 
     if A::REQUIRES_ASYNC && function.sig.asyncness.is_none() {
@@ -109,19 +106,26 @@ fn parse_input<A: EntryAttr>(input: TokenStream) -> Result<syn::ItemFn> {
     Ok(function)
 }
 
-fn _async_entry<A: EntryAttr>(_args: TokenStream, input: TokenStream) -> Result<TokenStream> {
+fn _async_entry<A: EntryAttr>(
+    _args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream
+) -> Result<TokenStream> {
     let function = parse_input::<A>(input)?;
     A::function(&function, &function.block).map(|t| t.into())
 }
 
-pub fn async_test_attribute(args: TokenStream, input: TokenStream) -> TokenStream {
-    _async_entry::<Test>(args, input).unwrap_or_else(|d| { d.emit(); TokenStream::new() })
+macro_rules! async_entry {
+    ($name:ident, $kind:ty, $default:expr) => (
+        pub fn $name(a: proc_macro::TokenStream, i: proc_macro::TokenStream) -> TokenStream {
+            _async_entry::<$kind>(a, i).unwrap_or_else(|d| {
+                let d = d.emit_as_tokens();
+                let default = $default;
+                quote!(#d #default)
+            })
+        }
+    )
 }
 
-pub fn main_attribute(args: TokenStream, input: TokenStream) -> TokenStream {
-    _async_entry::<Main>(args, input).unwrap_or_else(|d| { d.emit(); quote!(fn main() {}).into() })
-}
-
-pub fn launch_attribute(args: TokenStream, input: TokenStream) -> TokenStream {
-    _async_entry::<Launch>(args, input).unwrap_or_else(|d| { d.emit(); quote!(fn main() {}).into() })
-}
+async_entry!(async_test_attribute, Test, quote!());
+async_entry!(main_attribute, Main, quote!(fn main() {}));
+async_entry!(launch_attribute, Launch, quote!(fn main() {}));
diff --git a/core/codegen/src/attribute/catch.rs b/core/codegen/src/attribute/catch.rs
index 294d841a..2e9363d9 100644
--- a/core/codegen/src/attribute/catch.rs
+++ b/core/codegen/src/attribute/catch.rs
@@ -1,9 +1,9 @@
-use proc_macro::{TokenStream, Span};
-use devise::{syn, Spanned, Result, FromMeta};
-use crate::proc_macro2::TokenStream as TokenStream2;
+use devise::{syn, Spanned, Result, FromMeta, Diagnostic};
+use devise::ext::SpanDiagnosticExt;
 
+use crate::proc_macro2::{TokenStream, Span};
 use crate::http_codegen::Status;
-use crate::syn_ext::{syn_to_diag, IdentExt, ReturnTypeExt, TokenStreamExt};
+use crate::syn_ext::{IdentExt, ReturnTypeExt, TokenStreamExt};
 use self::syn::{Attribute, parse::Parser};
 use crate::{CATCH_FN_PREFIX, CATCH_STRUCT_PREFIX};
 
@@ -22,12 +22,16 @@ struct CatchParams {
     function: syn::ItemFn,
 }
 
-fn parse_params(args: TokenStream2, input: TokenStream) -> Result<CatchParams> {
-    let function: syn::ItemFn = syn::parse(input).map_err(syn_to_diag)
+fn parse_params(
+    args: TokenStream,
+    input: proc_macro::TokenStream
+) -> Result<CatchParams> {
+    let function: syn::ItemFn = syn::parse(input)
+        .map_err(Diagnostic::from)
         .map_err(|diag| diag.help("`#[catch]` can only be used on functions"))?;
 
     let full_attr = quote!(#[catch(#args)]);
-    let attrs = Attribute::parse_outer.parse2(full_attr).map_err(syn_to_diag)?;
+    let attrs = Attribute::parse_outer.parse2(full_attr)?;
     let attribute = match CatchAttribute::from_attrs("catch", &attrs) {
         Some(result) => result.map_err(|d| {
             d.help("`#[catch]` expects a single status integer, e.g.: #[catch(404)]")
@@ -38,9 +42,12 @@ fn parse_params(args: TokenStream2, input: TokenStream) -> Result<CatchParams> {
     Ok(CatchParams { status: attribute.status, function })
 }
 
-pub fn _catch(args: TokenStream, input: TokenStream) -> Result<TokenStream> {
+pub fn _catch(
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream
+) -> Result<TokenStream> {
     // Parse and validate all of the user's input.
-    let catch = parse_params(TokenStream2::from(args), input)?;
+    let catch = parse_params(args.into(), input)?;
 
     // Gather everything we'll need to generate the catcher.
     let user_catcher_fn = &catch.function;
@@ -124,9 +131,12 @@ pub fn _catch(args: TokenStream, input: TokenStream) -> Result<TokenStream> {
                 code: #status_code,
                 handler: #generated_fn_name,
             };
-    }.into())
+    })
 }
 
-pub fn catch_attribute(args: TokenStream, input: TokenStream) -> TokenStream {
-    _catch(args, input).unwrap_or_else(|d| { d.emit(); TokenStream::new() })
+pub fn catch_attribute(
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream
+) -> TokenStream {
+    _catch(args, input).unwrap_or_else(|d| d.emit_as_tokens())
 }
diff --git a/core/codegen/src/attribute/route.rs b/core/codegen/src/attribute/route.rs
index 9691db8e..698dafa8 100644
--- a/core/codegen/src/attribute/route.rs
+++ b/core/codegen/src/attribute/route.rs
@@ -2,17 +2,17 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 
-use proc_macro::{TokenStream, Span};
-use crate::proc_macro2::TokenStream as TokenStream2;
-use devise::{syn, Spanned, SpanWrapped, Result, FromMeta, ext::TypeExt};
+use devise::{syn, Spanned, SpanWrapped, Result, FromMeta, Diagnostic};
+use devise::ext::{SpanDiagnosticExt, TypeExt};
 use indexmap::IndexSet;
 
 use crate::proc_macro_ext::{Diagnostics, StringLit};
-use crate::syn_ext::{syn_to_diag, IdentExt};
-use self::syn::{Attribute, parse::Parser};
-
+use crate::syn_ext::IdentExt;
+use crate::proc_macro2::{TokenStream, Span};
 use crate::http_codegen::{Method, MediaType, RoutePath, DataSegment, Optional};
 use crate::attribute::segments::{Source, Kind, Segment};
+use crate::syn::{Attribute, parse::Parser};
+
 use crate::{ROUTE_FN_PREFIX, ROUTE_STRUCT_PREFIX, URI_MACRO_PREFIX, ROCKET_PARAM_PREFIX};
 
 /// The raw, parsed `#[route]` attribute.
@@ -59,9 +59,10 @@ fn parse_route(attr: RouteAttribute, function: syn::ItemFn) -> Result<Route> {
     if let Some(ref data) = attr.data {
         if !attr.method.0.supports_payload() {
             let msg = format!("'{}' does not typically support payloads", attr.method.0);
+            // FIXME(diag: warning)
             data.full_span.warning("`data` used with non-payload-supporting method")
                 .span_note(attr.method.span, msg)
-                .emit()
+                .emit_as_tokens();
         }
     }
 
@@ -127,10 +128,10 @@ fn parse_route(attr: RouteAttribute, function: syn::ItemFn) -> Result<Route> {
     diags.head_err_or(Route { attribute: attr, function, inputs, segments })
 }
 
-fn param_expr(seg: &Segment, ident: &syn::Ident, ty: &syn::Type) -> TokenStream2 {
+fn param_expr(seg: &Segment, ident: &syn::Ident, ty: &syn::Type) -> TokenStream {
     define_vars_and_mods!(req, data, error, log, request, _None, _Some, _Ok, _Err, Outcome);
     let i = seg.index.expect("dynamic parameters must be indexed");
-    let span = ident.span().unstable().join(ty.span()).unwrap().into();
+    let span = ident.span().join(ty.span()).unwrap_or_else(|| ty.span());
     let name = ident.to_string();
 
     // All dynamic parameter should be found if this function is being called;
@@ -175,9 +176,9 @@ fn param_expr(seg: &Segment, ident: &syn::Ident, ty: &syn::Type) -> TokenStream2
     }
 }
 
-fn data_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream2 {
+fn data_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream {
     define_vars_and_mods!(req, data, FromTransformedData, Outcome, Transform);
-    let span = ident.span().unstable().join(ty.span()).unwrap().into();
+    let span = ident.span().join(ty.span()).unwrap_or_else(|| ty.span());
     quote_spanned! { span =>
         let __transform = <#ty as #FromTransformedData>::transform(#req, #data).await;
 
@@ -204,7 +205,7 @@ fn data_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream2 {
     }
 }
 
-fn query_exprs(route: &Route) -> Option<TokenStream2> {
+fn query_exprs(route: &Route) -> Option<TokenStream> {
     define_vars_and_mods!(_None, _Some, _Ok, _Err, _Option);
     define_vars_and_mods!(data, trail, log, request, req, Outcome, SmallVec, Query);
     let query_segments = route.attribute.path.query.as_ref()?;
@@ -217,7 +218,7 @@ fn query_exprs(route: &Route) -> Option<TokenStream2> {
                 .map(|(_, rocket_ident, ty)| (rocket_ident, ty))
                 .unwrap();
 
-            let span = ident.span().unstable().join(ty.span()).unwrap();
+            let span = ident.span().join(ty.span()).unwrap_or_else(|| ty.span());
             (Some(ident), Some(ty), span.into())
         } else {
             (None, None, segment.span.into())
@@ -309,9 +310,9 @@ fn query_exprs(route: &Route) -> Option<TokenStream2> {
     })
 }
 
-fn request_guard_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream2 {
+fn request_guard_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream {
     define_vars_and_mods!(req, data, request, Outcome);
-    let span = ident.span().unstable().join(ty.span()).unwrap().into();
+    let span = ident.span().join(ty.span()).unwrap_or_else(|| ty.span());
     quote_spanned! { span =>
         #[allow(non_snake_case, unreachable_patterns, unreachable_code)]
         let #ident: #ty = match <#ty as #request::FromRequest>::from_request(#req).await {
@@ -322,7 +323,7 @@ fn request_guard_expr(ident: &syn::Ident, ty: &syn::Type) -> TokenStream2 {
     }
 }
 
-fn generate_internal_uri_macro(route: &Route) -> TokenStream2 {
+fn generate_internal_uri_macro(route: &Route) -> TokenStream {
     // Keep a global counter (+ thread ID later) to generate unique ids.
     static COUNTER: AtomicUsize = AtomicUsize::new(0);
 
@@ -344,7 +345,7 @@ fn generate_internal_uri_macro(route: &Route) -> TokenStream2 {
     let inner_generated_macro_name = generated_macro_name.append(&hasher.finish().to_string());
     let route_uri = route.attribute.path.origin.0.to_string();
 
-    quote! {
+    quote_spanned! { Span::call_site() =>
         #[doc(hidden)]
         #[macro_export]
         macro_rules! #inner_generated_macro_name {
@@ -360,7 +361,7 @@ fn generate_internal_uri_macro(route: &Route) -> TokenStream2 {
     }
 }
 
-fn generate_respond_expr(route: &Route) -> TokenStream2 {
+fn generate_respond_expr(route: &Route) -> TokenStream {
     let ret_span = match route.function.sig.output {
         syn::ReturnType::Default => route.function.sig.ident.span(),
         syn::ReturnType::Type(_, ref ty) => ty.span().into()
@@ -460,12 +461,13 @@ fn codegen_route(route: Route) -> Result<TokenStream> {
     }.into())
 }
 
-fn complete_route(args: TokenStream2, input: TokenStream) -> Result<TokenStream> {
-    let function: syn::ItemFn = syn::parse(input).map_err(syn_to_diag)
+fn complete_route(args: TokenStream, input: TokenStream) -> Result<TokenStream> {
+    let function: syn::ItemFn = syn::parse2(input)
+        .map_err(|e| Diagnostic::from(e))
         .map_err(|diag| diag.help("`#[route]` can only be used on functions"))?;
 
     let full_attr = quote!(#[route(#args)]);
-    let attrs = Attribute::parse_outer.parse2(full_attr).map_err(syn_to_diag)?;
+    let attrs = Attribute::parse_outer.parse2(full_attr)?;
     let attribute = match RouteAttribute::from_attrs("route", &attrs) {
         Some(result) => result?,
         None => return Err(Span::call_site().error("internal error: bad attribute"))
@@ -476,7 +478,7 @@ fn complete_route(args: TokenStream2, input: TokenStream) -> Result<TokenStream>
 
 fn incomplete_route(
     method: crate::http::Method,
-    args: TokenStream2,
+    args: TokenStream,
     input: TokenStream
 ) -> Result<TokenStream> {
     let method_str = method.to_string().to_lowercase();
@@ -486,11 +488,12 @@ fn incomplete_route(
 
     let method_ident = syn::Ident::new(&method_str, method_span.into());
 
-    let function: syn::ItemFn = syn::parse(input).map_err(syn_to_diag)
+    let function: syn::ItemFn = syn::parse2(input)
+        .map_err(|e| Diagnostic::from(e))
         .map_err(|d| d.help(format!("#[{}] can only be used on functions", method_str)))?;
 
     let full_attr = quote!(#[#method_ident(#args)]);
-    let attrs = Attribute::parse_outer.parse2(full_attr).map_err(syn_to_diag)?;
+    let attrs = Attribute::parse_outer.parse2(full_attr)?;
     let method_attribute = match MethodRouteAttribute::from_attrs(&method_str, &attrs) {
         Some(result) => result?,
         None => return Err(Span::call_site().error("internal error: bad attribute"))
@@ -511,13 +514,13 @@ fn incomplete_route(
 
 pub fn route_attribute<M: Into<Option<crate::http::Method>>>(
     method: M,
-    args: TokenStream,
-    input: TokenStream
+    args: proc_macro::TokenStream,
+    input: proc_macro::TokenStream
 ) -> TokenStream {
     let result = match method.into() {
-        Some(method) => incomplete_route(method, args.into(), input),
-        None => complete_route(args.into(), input)
+        Some(method) => incomplete_route(method, args.into(), input.into()),
+        None => complete_route(args.into(), input.into())
     };
 
-    result.unwrap_or_else(|diag| { diag.emit(); TokenStream::new() })
+    result.unwrap_or_else(|diag| diag.emit_as_tokens())
 }
diff --git a/core/codegen/src/attribute/segments.rs b/core/codegen/src/attribute/segments.rs
index b1aa62d5..e306db1f 100644
--- a/core/codegen/src/attribute/segments.rs
+++ b/core/codegen/src/attribute/segments.rs
@@ -1,7 +1,7 @@
 use std::hash::{Hash, Hasher};
 
-use devise::syn;
-use proc_macro::{Span, Diagnostic};
+use devise::{syn, Diagnostic, ext::SpanDiagnosticExt};
+use crate::proc_macro2::Span;
 
 use crate::http::uri::{UriPart, Path};
 use crate::http::route::RouteSegment;
@@ -36,7 +36,7 @@ impl From<&syn::Ident> for Segment {
         Segment {
             kind: Kind::Static,
             source: Source::Unknown,
-            span: ident.span().unstable(),
+            span: ident.span(),
             name: ident.to_string(),
             index: None,
         }
diff --git a/core/codegen/src/bang/mod.rs b/core/codegen/src/bang/mod.rs
index ca633c0c..fd05a192 100644
--- a/core/codegen/src/bang/mod.rs
+++ b/core/codegen/src/bang/mod.rs
@@ -1,9 +1,9 @@
-use proc_macro::TokenStream;
-use crate::proc_macro2::TokenStream as TokenStream2;
+use devise::Result;
 
-use devise::{syn, Spanned, Result};
-use self::syn::{Path, punctuated::Punctuated, parse::Parser, token::Comma};
-use crate::syn_ext::{IdentExt, syn_to_diag};
+use crate::syn_ext::IdentExt;
+use crate::syn::{Path, punctuated::Punctuated, parse::Parser, Token};
+use crate::syn::spanned::Spanned;
+use crate::proc_macro2::TokenStream;
 use crate::{ROUTE_STRUCT_PREFIX, CATCH_STRUCT_PREFIX};
 
 mod uri;
@@ -17,13 +17,11 @@ pub fn prefix_last_segment(path: &mut Path, prefix: &str) {
 
 fn _prefixed_vec(
     prefix: &str,
-    input: TokenStream,
-    ty: &TokenStream2
-) -> Result<TokenStream2> {
+    input: proc_macro::TokenStream,
+    ty: &TokenStream
+) -> Result<TokenStream> {
     // Parse a comma-separated list of paths.
-    let mut paths = <Punctuated<Path, Comma>>::parse_terminated
-        .parse(input)
-        .map_err(syn_to_diag)?;
+    let mut paths = <Punctuated<Path, Token![,]>>::parse_terminated.parse(input)?;
 
     // Prefix the last segment in each path with `prefix`.
     paths.iter_mut().for_each(|p| prefix_last_segment(p, prefix));
@@ -35,39 +33,46 @@ fn _prefixed_vec(
     Ok(quote!(vec![#(#prefixed_mapped_paths),*]))
 }
 
-fn prefixed_vec(prefix: &str, input: TokenStream, ty: TokenStream2) -> TokenStream {
-    let vec = _prefixed_vec(prefix, input, &ty)
-        .map_err(|diag| diag.emit())
-        .unwrap_or_else(|_| quote!(vec![]));
-
-    quote!({
-        let __vector: Vec<#ty> = #vec;
-        __vector
-    }).into()
+fn prefixed_vec(
+    prefix: &str,
+    input: proc_macro::TokenStream,
+    ty: TokenStream
+) -> TokenStream {
+    define_vars_and_mods!(_Vec);
+    _prefixed_vec(prefix, input, &ty)
+        .map(|vec| quote!({
+            let __vector: #_Vec<#ty> = #vec;
+            __vector
+        }))
+        .unwrap_or_else(|diag| {
+            let diag_tokens = diag.emit_as_tokens();
+            quote!({
+                #diag_tokens
+                let __vec: #_Vec<#ty> = vec![];
+                __vec
+            })
+        })
 }
 
-pub fn routes_macro(input: TokenStream) -> TokenStream {
+pub fn routes_macro(input: proc_macro::TokenStream) -> TokenStream {
     prefixed_vec(ROUTE_STRUCT_PREFIX, input, quote!(::rocket::Route))
 }
 
-pub fn catchers_macro(input: TokenStream) -> TokenStream {
+pub fn catchers_macro(input: proc_macro::TokenStream) -> TokenStream {
     prefixed_vec(CATCH_STRUCT_PREFIX, input, quote!(::rocket::Catcher))
 }
 
-pub fn uri_macro(input: TokenStream) -> TokenStream {
-    uri::_uri_macro(input)
-        .map_err(|diag| diag.emit())
-        .unwrap_or_else(|_| quote!(()).into())
+pub fn uri_macro(input: proc_macro::TokenStream) -> TokenStream {
+    uri::_uri_macro(input.into())
+        .unwrap_or_else(|diag| diag.emit_as_tokens())
 }
 
-pub fn uri_internal_macro(input: TokenStream) -> TokenStream {
-    uri::_uri_internal_macro(input)
-        .map_err(|diag| diag.emit())
-        .unwrap_or_else(|_| quote!(()).into())
+pub fn uri_internal_macro(input: proc_macro::TokenStream) -> TokenStream {
+    uri::_uri_internal_macro(input.into())
+        .unwrap_or_else(|diag| diag.emit_as_tokens())
 }
 
-pub fn guide_tests_internal(input: TokenStream) -> TokenStream {
+pub fn guide_tests_internal(input: proc_macro::TokenStream) -> TokenStream {
     test_guide::_macro(input)
-        .map_err(|diag| diag.emit())
-        .unwrap_or_else(|_| quote!(()).into())
+        .unwrap_or_else(|diag| diag.emit_as_tokens())
 }
diff --git a/core/codegen/src/bang/test_guide.rs b/core/codegen/src/bang/test_guide.rs
index 971c2c23..906d1ad2 100644
--- a/core/codegen/src/bang/test_guide.rs
+++ b/core/codegen/src/bang/test_guide.rs
@@ -1,16 +1,14 @@
 use std::path::Path;
 use std::error::Error;
 
-use proc_macro::TokenStream;
-use devise::{syn::{self, Ident, LitStr}, Result};
+use devise::ext::SpanDiagnosticExt;
+use devise::syn::{self, Ident, LitStr};
+use devise::proc_macro2::TokenStream;
 
-use crate::syn_ext::syn_to_diag;
-use crate::proc_macro2::TokenStream as TokenStream2;
-
-pub fn _macro(input: TokenStream) -> Result<TokenStream> {
-    let root_glob = syn::parse::<LitStr>(input.into()).map_err(syn_to_diag)?;
+pub fn _macro(input: proc_macro::TokenStream) -> devise::Result<TokenStream> {
+    let root_glob = syn::parse::<LitStr>(input.into())?;
     let modules = entry_to_modules(&root_glob)
-        .map_err(|e| root_glob.span().unstable().error(format!("failed to read: {}", e)))?;
+        .map_err(|e| root_glob.span().error(format!("failed to read: {}", e)))?;
 
     Ok(quote_spanned!(root_glob.span() =>
         #[allow(dead_code)]
@@ -19,7 +17,7 @@ pub fn _macro(input: TokenStream) -> Result<TokenStream> {
     ).into())
 }
 
-fn entry_to_modules(root_glob: &LitStr) -> std::result::Result<Vec<TokenStream2>, Box<dyn Error>> {
+fn entry_to_modules(root_glob: &LitStr) -> Result<Vec<TokenStream>, Box<dyn Error>> {
     let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").expect("MANIFEST_DIR");
     let full_glob = Path::new(&manifest_dir).join(&root_glob.value()).display().to_string();
 
diff --git a/core/codegen/src/bang/uri.rs b/core/codegen/src/bang/uri.rs
index 77cbda84..f7fe7d83 100644
--- a/core/codegen/src/bang/uri.rs
+++ b/core/codegen/src/bang/uri.rs
@@ -1,15 +1,15 @@
 use std::fmt::Display;
-use proc_macro::TokenStream;
-use crate::proc_macro2::TokenStream as TokenStream2;
 
-use devise::{syn, Result};
-use devise::syn::{Expr, Ident, Type, spanned::Spanned};
+use devise::{syn, Result, ext::SpanDiagnosticExt};
+
 use crate::http::{uri::{Origin, Path, Query}, ext::IntoOwned};
 use crate::http::route::{RouteSegment, Kind, Source};
 
+use crate::syn::{Expr, Ident, Type, spanned::Spanned};
 use crate::http_codegen::Optional;
-use crate::syn_ext::{IdentExt, syn_to_diag};
+use crate::syn_ext::IdentExt;
 use crate::bang::{prefix_last_segment, uri_parsing::*};
+use crate::proc_macro2::TokenStream;
 
 use crate::URI_MACRO_PREFIX;
 
@@ -24,12 +24,12 @@ macro_rules! p {
 }
 
 pub fn _uri_macro(input: TokenStream) -> Result<TokenStream> {
-    let input2: TokenStream2 = input.clone().into();
-    let mut params = syn::parse::<UriParams>(input).map_err(syn_to_diag)?;
+    let input2: TokenStream = input.clone().into();
+    let mut params = syn::parse2::<UriParams>(input)?;
     prefix_last_segment(&mut params.route_path, URI_MACRO_PREFIX);
 
     let path = &params.route_path;
-    Ok(quote!(#path!(#input2)).into())
+    Ok(quote!(#path!(#input2)))
 }
 
 fn extract_exprs<'a>(internal: &'a InternalUriParams) -> Result<(
@@ -43,8 +43,7 @@ fn extract_exprs<'a>(internal: &'a InternalUriParams) -> Result<(
             let path_param_count = internal.route_uri.path().matches('<').count();
             for expr in exprs.iter().take(path_param_count) {
                 if !expr.as_expr().is_some() {
-                    return Err(expr.span().unstable()
-                               .error("path parameters cannot be ignored"));
+                    return Err(expr.span().error("path parameters cannot be ignored"));
                 }
             }
 
@@ -91,13 +90,13 @@ fn extract_exprs<'a>(internal: &'a InternalUriParams) -> Result<(
 
             if !extra.is_empty() {
                 let (ps, msg) = join(extra.iter());
-                let spans: Vec<_> = extra.iter().map(|ident| ident.span().unstable()).collect();
+                let spans: Vec<_> = extra.iter().map(|ident| ident.span()).collect();
                 diag = diag.span_help(spans, format!("unknown {}: {}", ps, msg));
             }
 
             if !dup.is_empty() {
                 let (ps, msg) = join(dup.iter());
-                let spans: Vec<_> = dup.iter().map(|ident| ident.span().unstable()).collect();
+                let spans: Vec<_> = dup.iter().map(|ident| ident.span()).collect();
                 diag = diag.span_help(spans, format!("duplicate {}: {}", ps, msg));
             }
 
@@ -106,7 +105,7 @@ fn extract_exprs<'a>(internal: &'a InternalUriParams) -> Result<(
     }
 }
 
-fn add_binding(to: &mut Vec<TokenStream2>, ident: &Ident, ty: &Type, expr: &Expr, source: Source) {
+fn add_binding(to: &mut Vec<TokenStream>, ident: &Ident, ty: &Type, expr: &Expr, source: Source) {
     let uri_mod = quote!(rocket::http::uri);
     let (span, ident_tmp) = (expr.span(), ident.prepend("__tmp_"));
     let from_uri_param = if source == Source::Query {
@@ -124,9 +123,9 @@ fn add_binding(to: &mut Vec<TokenStream2>, ident: &Ident, ty: &Type, expr: &Expr
 
 fn explode_path<'a, I: Iterator<Item = (&'a Ident, &'a Type, &'a Expr)>>(
     uri: &Origin<'_>,
-    bindings: &mut Vec<TokenStream2>,
+    bindings: &mut Vec<TokenStream>,
     mut items: I
-) -> TokenStream2 {
+) -> TokenStream {
     let (uri_mod, path) = (quote!(rocket::http::uri), uri.path());
     if !path.contains('<') {
         return quote!(#uri_mod::UriArgumentsKind::Static(#path));
@@ -153,9 +152,9 @@ fn explode_path<'a, I: Iterator<Item = (&'a Ident, &'a Type, &'a Expr)>>(
 
 fn explode_query<'a, I: Iterator<Item = (&'a Ident, &'a Type, &'a ArgExpr)>>(
     uri: &Origin<'_>,
-    bindings: &mut Vec<TokenStream2>,
+    bindings: &mut Vec<TokenStream>,
     mut items: I
-) -> Option<TokenStream2> {
+) -> Option<TokenStream> {
     let (uri_mod, query) = (quote!(rocket::http::uri), uri.query()?);
     if !query.contains('<') {
         return Some(quote!(#uri_mod::UriArgumentsKind::Static(#query)));
@@ -215,7 +214,7 @@ fn build_origin(internal: &InternalUriParams) -> Origin<'static> {
 
 pub fn _uri_internal_macro(input: TokenStream) -> Result<TokenStream> {
     // Parse the internal invocation and the user's URI param expressions.
-    let internal = syn::parse::<InternalUriParams>(input).map_err(syn_to_diag)?;
+    let internal = syn::parse2::<InternalUriParams>(input)?;
     let (path_params, query_params) = extract_exprs(&internal)?;
 
     let mut bindings = vec![];
@@ -227,5 +226,5 @@ pub fn _uri_internal_macro(input: TokenStream) -> Result<TokenStream> {
      Ok(quote!({
          #(#bindings)*
          #uri_mod::UriArguments { path: #path, query: #query, }.into_origin()
-     }).into())
+     }))
 }
diff --git a/core/codegen/src/bang/uri_parsing.rs b/core/codegen/src/bang/uri_parsing.rs
index ab6edf8b..63ba28ad 100644
--- a/core/codegen/src/bang/uri_parsing.rs
+++ b/core/codegen/src/bang/uri_parsing.rs
@@ -1,16 +1,15 @@
-use proc_macro::Span;
-
-use devise::{syn, Spanned};
-use devise::proc_macro2::TokenStream as TokenStream2;
-use devise::ext::TypeExt;
+use indexmap::IndexMap;
+use devise::{Spanned, ext::TypeExt};
 use quote::ToTokens;
 
-use self::syn::{Expr, Ident, LitStr, Path, Token, Type};
-use self::syn::parse::{self, Parse, ParseStream};
-use self::syn::punctuated::Punctuated;
+use crate::syn::{self, Expr, Ident, LitStr, Path, Token, Type};
+use crate::syn::parse::{self, Parse, ParseStream};
+use crate::syn::punctuated::Punctuated;
 
 use crate::http::{uri::Origin, ext::IntoOwned};
-use indexmap::IndexMap;
+use crate::proc_macro2::{TokenStream, Span};
+
+// TODO(diag): Use 'Diagnostic' in place of syn::Error.
 
 #[derive(Debug)]
 pub enum ArgExpr {
@@ -124,7 +123,7 @@ impl Parse for UriParams {
             })?;
 
             if !input.peek(Token![,]) && input.cursor().eof() {
-                return err(string.span().unstable(), "unexpected end of input: \
+                return err(string.span(), "unexpected end of input: \
                     expected ',' followed by route path");
             }
 
@@ -327,7 +326,7 @@ impl ArgExpr {
 }
 
 impl ToTokens for ArgExpr {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         match self {
             ArgExpr::Expr(e) => e.to_tokens(tokens),
             ArgExpr::Ignored(e) => e.to_tokens(tokens)
@@ -336,7 +335,7 @@ impl ToTokens for ArgExpr {
 }
 
 impl ToTokens for Arg {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         match self {
             Arg::Unnamed(e) => e.to_tokens(tokens),
             Arg::Named(ident, eq, expr) => tokens.extend(quote!(#ident #eq #expr)),
@@ -345,7 +344,7 @@ impl ToTokens for Arg {
 }
 
 impl ToTokens for Args {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         match self {
             Args::Unnamed(e) | Args::Named(e) => e.to_tokens(tokens)
         }
diff --git a/core/codegen/src/derive/from_form.rs b/core/codegen/src/derive/from_form.rs
index 5b906a70..67531df4 100644
--- a/core/codegen/src/derive/from_form.rs
+++ b/core/codegen/src/derive/from_form.rs
@@ -1,5 +1,6 @@
-use proc_macro::{Span, TokenStream};
-use devise::{*, ext::{TypeExt, Split3}};
+use devise::{*, ext::{TypeExt, Split3, SpanDiagnosticExt}};
+
+use crate::proc_macro2::{Span, TokenStream};
 
 #[derive(FromMeta)]
 pub struct Form {
@@ -57,7 +58,7 @@ fn validate_struct(gen: &DeriveGenerator, data: Struct<'_>) -> Result<()> {
     Ok(())
 }
 
-pub fn derive_from_form(input: TokenStream) -> TokenStream {
+pub fn derive_from_form(input: proc_macro::TokenStream) -> TokenStream {
     let form_error = quote!(::rocket::request::FormParseError);
     DeriveGenerator::build_for(input, quote!(impl<'__f> ::rocket::request::FromForm<'__f>))
         .generic_support(GenericSupport::Lifetime | GenericSupport::Type)
@@ -126,5 +127,5 @@ pub fn derive_from_form(input: TokenStream) -> TokenStream {
                 #_Ok(Self { #(#builders)* })
             })
         })
-        .to_tokens()
+        .to_tokens2()
 }
diff --git a/core/codegen/src/derive/from_form_value.rs b/core/codegen/src/derive/from_form_value.rs
index aa796d63..30ef3697 100644
--- a/core/codegen/src/derive/from_form_value.rs
+++ b/core/codegen/src/derive/from_form_value.rs
@@ -1,12 +1,13 @@
-use devise::*;
-use proc_macro::TokenStream;
+use devise::{*, ext::SpanDiagnosticExt};
+
+use crate::proc_macro2::TokenStream;
 
 #[derive(FromMeta)]
 struct Form {
     value: String,
 }
 
-pub fn derive_from_form_value(input: TokenStream) -> TokenStream {
+pub fn derive_from_form_value(input: proc_macro::TokenStream) -> TokenStream {
     define_vars_and_mods!(_Ok, _Err, _Result);
     DeriveGenerator::build_for(input, quote!(impl<'__v> ::rocket::request::FromFormValue<'__v>))
         .generic_support(GenericSupport::None)
@@ -21,7 +22,8 @@ pub fn derive_from_form_value(input: TokenStream) -> TokenStream {
 
             // Emit a warning if the enum is empty.
             if data.variants.is_empty() {
-                generator.input.span().warning("deriving for empty enum").emit();
+                return Err(generator.input.span()
+                    .error("enum must have at least one field"));
             }
 
             Ok(())
@@ -51,5 +53,5 @@ pub fn derive_from_form_value(input: TokenStream) -> TokenStream {
                 }
             })
         })
-        .to_tokens()
+        .to_tokens2()
 }
diff --git a/core/codegen/src/derive/responder.rs b/core/codegen/src/derive/responder.rs
index 3c7bae76..abd2b8ba 100644
--- a/core/codegen/src/derive/responder.rs
+++ b/core/codegen/src/derive/responder.rs
@@ -1,8 +1,8 @@
-use quote::ToTokens;
-use proc_macro::TokenStream;
-use devise::{*, ext::TypeExt};
-use devise::proc_macro2::TokenStream as TokenStream2;
 
+use quote::ToTokens;
+use devise::{*, ext::{TypeExt, SpanDiagnosticExt}};
+
+use crate::proc_macro2::TokenStream;
 use crate::http_codegen::{ContentType, Status};
 
 #[derive(Default, FromMeta)]
@@ -16,15 +16,11 @@ struct FieldAttr {
     ignore: bool,
 }
 
-pub fn derive_responder(input: TokenStream) -> TokenStream {
-    // NOTE: Due to a bug in devise, we can't do the more correct:
-    // quote!(impl<'__r, '__o: '__r> ::rocket::response::Responder<'__r, '__o>))
-    // replace_generic(1, 0)
-    // A bugfix (on devise master) fixes this so the above works. Hack.
-    DeriveGenerator::build_for(input, quote!(impl<'__r> ::rocket::response::Responder<'__r, '__r>))
+pub fn derive_responder(input: proc_macro::TokenStream) -> TokenStream {
+    DeriveGenerator::build_for(input, quote!(impl<'__r, '__o: '__r> ::rocket::response::Responder<'__r, '__o>))
         .generic_support(GenericSupport::Lifetime)
         .data_support(DataSupport::Struct | DataSupport::Enum)
-        .replace_generic(0, 0)
+        .replace_generic(1, 0)
         .validate_generics(|_, generics| match generics.lifetimes().count() > 1 {
             true => Err(generics.span().error("only one lifetime is supported")),
             false => Ok(())
@@ -37,13 +33,13 @@ pub fn derive_responder(input: TokenStream) -> TokenStream {
             fn respond_to(
                 self,
                 __req: &'__r ::rocket::request::Request
-            ) -> ::rocket::response::Result<'__r> {
+            ) -> ::rocket::response::Result<'__o> {
                 #inner
             }
         })
         .try_map_fields(|_, fields| {
             define_vars_and_mods!(_Ok);
-            fn set_header_tokens<T: ToTokens + Spanned>(item: T) -> TokenStream2 {
+            fn set_header_tokens<T: ToTokens + Spanned>(item: T) -> TokenStream {
                 quote_spanned!(item.span().into() => __res.set_header(#item);)
             }
 
@@ -82,5 +78,5 @@ pub fn derive_responder(input: TokenStream) -> TokenStream {
                 #_Ok(__res)
             })
         })
-        .to_tokens()
+        .to_tokens2()
 }
diff --git a/core/codegen/src/derive/uri_display.rs b/core/codegen/src/derive/uri_display.rs
index aaf0fb94..521dc984 100644
--- a/core/codegen/src/derive/uri_display.rs
+++ b/core/codegen/src/derive/uri_display.rs
@@ -1,8 +1,8 @@
-use proc_macro::{Span, TokenStream};
-use devise::*;
+
+use devise::{*, ext::SpanDiagnosticExt};
 
 use crate::derive::from_form::Form;
-use crate::proc_macro2::TokenStream as TokenStream2;
+use crate::proc_macro2::{TokenStream, Span};
 
 const NO_EMPTY_FIELDS: &str = "fieldless structs or variants are not supported";
 const NO_NULLARY: &str = "nullary items are not supported";
@@ -39,7 +39,7 @@ fn validate_enum(gen: &DeriveGenerator, data: Enum<'_>) -> Result<()> {
 }
 
 #[allow(non_snake_case)]
-pub fn derive_uri_display_query(input: TokenStream) -> TokenStream {
+pub fn derive_uri_display_query(input: proc_macro::TokenStream) -> TokenStream {
     let Query = quote!(::rocket::http::uri::Query);
     let UriDisplay = quote!(::rocket::http::uri::UriDisplay<#Query>);
     let Formatter = quote!(::rocket::http::uri::Formatter<#Query>);
@@ -116,15 +116,15 @@ pub fn derive_uri_display_query(input: TokenStream) -> TokenStream {
         })
         .to_tokens();
 
-    let mut ts = TokenStream2::from(uri_display);
-    ts.extend(TokenStream2::from(from_self));
-    ts.extend(TokenStream2::from(from_ref));
-    ts.extend(TokenStream2::from(from_mut));
+    let mut ts = TokenStream::from(uri_display);
+    ts.extend(TokenStream::from(from_self));
+    ts.extend(TokenStream::from(from_ref));
+    ts.extend(TokenStream::from(from_mut));
     ts.into()
 }
 
 #[allow(non_snake_case)]
-pub fn derive_uri_display_path(input: TokenStream) -> TokenStream {
+pub fn derive_uri_display_path(input: proc_macro::TokenStream) -> TokenStream {
     let Path = quote!(::rocket::http::uri::Path);
     let UriDisplay = quote!(::rocket::http::uri::UriDisplay<#Path>);
     let Formatter = quote!(::rocket::http::uri::Formatter<#Path>);
@@ -179,8 +179,8 @@ pub fn derive_uri_display_path(input: TokenStream) -> TokenStream {
         })
         .to_tokens();
 
-    let mut ts = TokenStream2::from(uri_display);
-    ts.extend(TokenStream2::from(from_self));
-    ts.extend(TokenStream2::from(from_ref));
+    let mut ts = TokenStream::from(uri_display);
+    ts.extend(TokenStream::from(from_self));
+    ts.extend(TokenStream::from(from_ref));
     ts.into()
 }
diff --git a/core/codegen/src/http_codegen.rs b/core/codegen/src/http_codegen.rs
index 1281bd16..823673cd 100644
--- a/core/codegen/src/http_codegen.rs
+++ b/core/codegen/src/http_codegen.rs
@@ -1,6 +1,7 @@
 use quote::ToTokens;
-use crate::proc_macro2::TokenStream as TokenStream2;
-use devise::{FromMeta, MetaItem, Result, ext::{Split2, PathExt}};
+use devise::{FromMeta, MetaItem, Result, ext::{Split2, PathExt, SpanDiagnosticExt}};
+
+use crate::proc_macro2::TokenStream;
 use crate::http::{self, ext::IntoOwned};
 use crate::http::uri::{Path, Query};
 use crate::attribute::segments::{parse_segments, parse_data_segment, Segment, Kind};
@@ -53,7 +54,7 @@ impl FromMeta for Status {
 }
 
 impl ToTokens for Status {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         let (code, reason) = (self.0.code, self.0.reason);
         tokens.extend(quote!(rocket::http::Status { code: #code, reason: #reason }));
     }
@@ -68,7 +69,7 @@ impl FromMeta for ContentType {
 }
 
 impl ToTokens for ContentType {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         // Yeah, yeah. (((((i))).kn0w()))
         let media_type = MediaType((self.0).clone().0);
         tokens.extend(quote!(::rocket::http::ContentType(#media_type)));
@@ -81,9 +82,10 @@ impl FromMeta for MediaType {
             .ok_or(meta.value_span().error("invalid or unknown media type"))?;
 
         if !mt.is_known() {
+            // FIXME(diag: warning)
             meta.value_span()
                 .warning(format!("'{}' is not a known media type", mt))
-                .emit();
+                .emit_as_tokens();
         }
 
         Ok(MediaType(mt))
@@ -91,7 +93,7 @@ impl FromMeta for MediaType {
 }
 
 impl ToTokens for MediaType {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         use std::iter::repeat;
         let (top, sub) = (self.0.top().as_str(), self.0.sub().as_str());
         let (keys, values) = self.0.params().split2();
@@ -150,7 +152,7 @@ impl FromMeta for Method {
 }
 
 impl ToTokens for Method {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         let method_tokens = match self.0 {
             http::Method::Get => quote!(::rocket::http::Method::Get),
             http::Method::Put => quote!(::rocket::http::Method::Put),
@@ -234,7 +236,7 @@ impl FromMeta for RoutePath {
 }
 
 impl<T: ToTokens> ToTokens for Optional<T> {
-    fn to_tokens(&self, tokens: &mut TokenStream2) {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
         define_vars_and_mods!(_Some, _None);
         let opt_tokens = match self.0 {
             Some(ref val) => quote!(#_Some(#val)),
diff --git a/core/codegen/src/lib.rs b/core/codegen/src/lib.rs
index 39d8f151..2ee24ad2 100644
--- a/core/codegen/src/lib.rs
+++ b/core/codegen/src/lib.rs
@@ -1,4 +1,3 @@
-#![feature(proc_macro_diagnostic, proc_macro_span)]
 #![recursion_limit="128"]
 
 #![doc(html_root_url = "https://api.rocket.rs/v0.5")]
@@ -101,6 +100,7 @@ vars_and_mods! {
     _Ok => ::std::result::Result::Ok,
     _Err => ::std::result::Result::Err,
     _Box => ::std::boxed::Box,
+    _Vec => ::std::vec::Vec,
 }
 
 macro_rules! define_vars_and_mods {
@@ -118,7 +118,7 @@ mod syn_ext;
 
 use crate::http::Method;
 use proc_macro::TokenStream;
-use devise::proc_macro2;
+use devise::{proc_macro2, syn};
 
 static ROUTE_STRUCT_PREFIX: &str = "static_rocket_route_info_for_";
 static CATCH_STRUCT_PREFIX: &str = "static_rocket_catch_info_for_";
@@ -129,15 +129,19 @@ static ROCKET_PARAM_PREFIX: &str = "__rocket_param_";
 
 macro_rules! emit {
     ($tokens:expr) => ({
-        let tokens = $tokens;
+        use devise::ext::SpanDiagnosticExt;
+
+        let mut tokens = $tokens;
         if std::env::var_os("ROCKET_CODEGEN_DEBUG").is_some() {
-            proc_macro::Span::call_site()
+            let debug_tokens = proc_macro2::Span::call_site()
                 .note("emitting Rocket code generation debug output")
                 .note(tokens.to_string())
-                .emit()
+                .emit_as_tokens();
+
+            tokens.extend(debug_tokens);
         }
 
-        tokens
+        tokens.into()
     })
 }
 
diff --git a/core/codegen/src/proc_macro_ext.rs b/core/codegen/src/proc_macro_ext.rs
index 66e1359b..72776020 100644
--- a/core/codegen/src/proc_macro_ext.rs
+++ b/core/codegen/src/proc_macro_ext.rs
@@ -1,6 +1,8 @@
 use std::ops::RangeBounds;
 
-use proc_macro::{Span, Diagnostic, Literal};
+use devise::Diagnostic;
+
+use crate::proc_macro2::{Span, Literal};
 
 pub type PResult<T> = std::result::Result<T, Diagnostic>;
 
@@ -27,7 +29,8 @@ impl Diagnostics {
         let mut iter = self.0.into_iter();
         let mut last = iter.next().expect("Diagnostic::emit_head empty");
         for diag in iter {
-            last.emit();
+            // FIXME(diag: emit, can there be errors here?)
+            last.emit_as_tokens();
             last = diag;
         }
 
@@ -86,7 +89,8 @@ impl StringLit {
     }
 
     /// Attempt to obtain a subspan, or, failing that, produce the full span.
-    /// This will create suboptimal diagnostics, but better than failing to build entirely.
+    /// This will create suboptimal diagnostics, but better than failing to
+    /// build entirely.
     pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Span {
         self.1.subspan(range).unwrap_or_else(|| self.span())
     }
diff --git a/core/codegen/src/syn_ext.rs b/core/codegen/src/syn_ext.rs
index ef60d37b..736d48a5 100644
--- a/core/codegen/src/syn_ext.rs
+++ b/core/codegen/src/syn_ext.rs
@@ -1,11 +1,6 @@
 //! Extensions to `syn` types.
 
 use devise::syn;
-use proc_macro::Diagnostic;
-
-pub fn syn_to_diag(error: syn::parse::Error) -> Diagnostic {
-    error.span().unstable().error(error.to_string())
-}
 
 pub trait IdentExt {
     fn prepend(&self, string: &str) -> syn::Ident;
diff --git a/core/codegen/tests/ui-fail/from_form_value.rs b/core/codegen/tests/ui-fail/from_form_value.rs
index ccf44a93..ebc131df 100644
--- a/core/codegen/tests/ui-fail/from_form_value.rs
+++ b/core/codegen/tests/ui-fail/from_form_value.rs
@@ -22,7 +22,7 @@ enum Foo4 {
 
 #[derive(FromFormValue)]
 enum Foo5 { }
-//~^ WARNING empty enum
+//~^ ERROR at least one field
 
 #[derive(FromFormValue)]
 enum Foo6<T> {
diff --git a/core/codegen/tests/ui-fail/from_form_value.stderr b/core/codegen/tests/ui-fail/from_form_value.stderr
index f49e5468..d5fb24f9 100644
--- a/core/codegen/tests/ui-fail/from_form_value.stderr
+++ b/core/codegen/tests/ui-fail/from_form_value.stderr
@@ -53,11 +53,18 @@ note: error occurred while deriving `FromFormValue`
    |          ^^^^^^^^^^^^^
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-warning: deriving for empty enum
+error: enum must have at least one field
   --> $DIR/from_form_value.rs:24:1
    |
 24 | enum Foo5 { }
    | ^^^^^^^^^^^^^
+   |
+note: error occurred while deriving `FromFormValue`
+  --> $DIR/from_form_value.rs:23:10
+   |
+23 | #[derive(FromFormValue)]
+   |          ^^^^^^^^^^^^^
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: type generics are not supported
   --> $DIR/from_form_value.rs:28:11
@@ -98,5 +105,5 @@ note: error occurred while deriving `FromFormValue`
    |          ^^^^^^^^^^^^^
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 7 previous errors; 1 warning emitted
+error: aborting due to 8 previous errors
 
diff --git a/core/codegen/tests/ui-fail/uri_display.stderr b/core/codegen/tests/ui-fail/uri_display.stderr
index 9fa32284..a6348be0 100644
--- a/core/codegen/tests/ui-fail/uri_display.stderr
+++ b/core/codegen/tests/ui-fail/uri_display.stderr
@@ -51,10 +51,10 @@ note: error occurred while deriving `UriDisplay`
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: tuple structs or variants must have exactly one field
-  --> $DIR/uri_display.rs:39:12
+  --> $DIR/uri_display.rs:39:13
    |
 39 | struct Foo5(String, String);
-   |            ^^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^^
    |
 note: error occurred while deriving `UriDisplay`
   --> $DIR/uri_display.rs:35:10
@@ -77,10 +77,10 @@ note: error occurred while deriving `UriDisplay`
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: struct must have exactly one field
-  --> $DIR/uri_display.rs:55:12
+  --> $DIR/uri_display.rs:55:13
    |
 55 | struct Foo7(String, usize);
-   |            ^^^^^^^^^^^^^^^
+   |             ^^^^^^^^^^^^^
    |
 note: error occurred while deriving `UriDisplay`
   --> $DIR/uri_display.rs:52:10
diff --git a/examples/uuid/Cargo.toml b/examples/uuid/Cargo.toml
index d64ae72b..3744508a 100644
--- a/examples/uuid/Cargo.toml
+++ b/examples/uuid/Cargo.toml
@@ -8,7 +8,6 @@ publish = false
 [dependencies]
 rocket = { path = "../../core/lib" }
 lazy_static = "1.0"
-uuid = "0.8"
 
 [dependencies.rocket_contrib]
 default-features = false
diff --git a/examples/uuid/src/main.rs b/examples/uuid/src/main.rs
index 18f048c1..dfb5bf63 100644
--- a/examples/uuid/src/main.rs
+++ b/examples/uuid/src/main.rs
@@ -2,7 +2,9 @@
 #[macro_use] extern crate lazy_static;
 
 use std::collections::HashMap;
+
 use rocket_contrib::uuid::Uuid;
+use rocket_contrib::uuid::uuid_crate as uuid;
 
 #[cfg(test)] mod tests;