diff --git a/src/libsyntax/codemap.rs b/src/libsyntax/codemap.rs
index 8381adaea79..0a9991d33b1 100644
--- a/src/libsyntax/codemap.rs
+++ b/src/libsyntax/codemap.rs
@@ -131,7 +131,7 @@ pub(super) struct CodeMapFiles {
 
 pub struct CodeMap {
     pub(super) files: Lock<CodeMapFiles>,
-    file_loader: Box<FileLoader + Sync + Send>,
+    file_loader: Box<dyn FileLoader + Sync + Send>,
     // This is used to apply the file path remapping as specified via
     // --remap-path-prefix to all FileMaps allocated within this CodeMap.
     path_mapping: FilePathMapping,
@@ -162,7 +162,7 @@ impl CodeMap {
 
     }
 
-    pub fn with_file_loader(file_loader: Box<FileLoader + Sync + Send>,
+    pub fn with_file_loader(file_loader: Box<dyn FileLoader + Sync + Send>,
                             path_mapping: FilePathMapping)
                             -> CodeMap {
         CodeMap {
diff --git a/src/libsyntax/diagnostics/metadata.rs b/src/libsyntax/diagnostics/metadata.rs
index dc01a79190b..61b0579a3e7 100644
--- a/src/libsyntax/diagnostics/metadata.rs
+++ b/src/libsyntax/diagnostics/metadata.rs
@@ -73,7 +73,7 @@ fn get_metadata_path(directory: PathBuf, name: &str) -> PathBuf {
 /// For our current purposes the prefix is the target architecture and the name is a crate name.
 /// If an error occurs steps will be taken to ensure that no file is created.
 pub fn output_metadata(ecx: &ExtCtxt, prefix: &str, name: &str, err_map: &ErrorMap)
-    -> Result<(), Box<Error>>
+    -> Result<(), Box<dyn Error>>
 {
     // Create the directory to place the file in.
     let metadata_dir = get_metadata_dir(prefix);
diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index ca0293aca6e..72ce2740190 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -42,7 +42,7 @@ pub type ErrorMap = BTreeMap<Name, ErrorInfo>;
 pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,
                                    span: Span,
                                    token_tree: &[TokenTree])
-                                   -> Box<MacResult+'cx> {
+                                   -> Box<dyn MacResult+'cx> {
     let code = match (token_tree.len(), token_tree.get(0)) {
         (1, Some(&TokenTree::Token(_, token::Ident(code, _)))) => code,
         _ => unreachable!()
@@ -75,7 +75,7 @@ pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,
 pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
                                        span: Span,
                                        token_tree: &[TokenTree])
-                                       -> Box<MacResult+'cx> {
+                                       -> Box<dyn MacResult+'cx> {
     let (code, description) = match (
         token_tree.len(),
         token_tree.get(0),
@@ -145,7 +145,7 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
 pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
                                           span: Span,
                                           token_tree: &[TokenTree])
-                                          -> Box<MacResult+'cx> {
+                                          -> Box<dyn MacResult+'cx> {
     assert_eq!(token_tree.len(), 3);
     let (crate_name, name) = match (&token_tree[0], &token_tree[2]) {
         (
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 2e9c7d6f96c..e49a521040f 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -153,18 +153,18 @@ pub trait MultiItemDecorator {
               sp: Span,
               meta_item: &ast::MetaItem,
               item: &Annotatable,
-              push: &mut FnMut(Annotatable));
+              push: &mut dyn FnMut(Annotatable));
 }
 
 impl<F> MultiItemDecorator for F
-    where F : Fn(&mut ExtCtxt, Span, &ast::MetaItem, &Annotatable, &mut FnMut(Annotatable))
+    where F : Fn(&mut ExtCtxt, Span, &ast::MetaItem, &Annotatable, &mut dyn FnMut(Annotatable))
 {
     fn expand(&self,
               ecx: &mut ExtCtxt,
               sp: Span,
               meta_item: &ast::MetaItem,
               item: &Annotatable,
-              push: &mut FnMut(Annotatable)) {
+              push: &mut dyn FnMut(Annotatable)) {
         (*self)(ecx, sp, meta_item, item, push)
     }
 }
@@ -247,18 +247,19 @@ impl<F> AttrProcMacro for F
 /// Represents a thing that maps token trees to Macro Results
 pub trait TTMacroExpander {
     fn expand<'cx>(&self, ecx: &'cx mut ExtCtxt, span: Span, input: TokenStream)
-                   -> Box<MacResult+'cx>;
+                   -> Box<dyn MacResult+'cx>;
 }
 
 pub type MacroExpanderFn =
     for<'cx> fn(&'cx mut ExtCtxt, Span, &[tokenstream::TokenTree])
-                -> Box<MacResult+'cx>;
+                -> Box<dyn MacResult+'cx>;
 
 impl<F> TTMacroExpander for F
-    where F: for<'cx> Fn(&'cx mut ExtCtxt, Span, &[tokenstream::TokenTree]) -> Box<MacResult+'cx>
+    where F: for<'cx> Fn(&'cx mut ExtCtxt, Span, &[tokenstream::TokenTree])
+    -> Box<dyn MacResult+'cx>
 {
     fn expand<'cx>(&self, ecx: &'cx mut ExtCtxt, span: Span, input: TokenStream)
-                   -> Box<MacResult+'cx> {
+                   -> Box<dyn MacResult+'cx> {
         struct AvoidInterpolatedIdents;
 
         impl Folder for AvoidInterpolatedIdents {
@@ -289,23 +290,23 @@ pub trait IdentMacroExpander {
                    sp: Span,
                    ident: ast::Ident,
                    token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<MacResult+'cx>;
+                   -> Box<dyn MacResult+'cx>;
 }
 
 pub type IdentMacroExpanderFn =
     for<'cx> fn(&'cx mut ExtCtxt, Span, ast::Ident, Vec<tokenstream::TokenTree>)
-                -> Box<MacResult+'cx>;
+                -> Box<dyn MacResult+'cx>;
 
 impl<F> IdentMacroExpander for F
     where F : for<'cx> Fn(&'cx mut ExtCtxt, Span, ast::Ident,
-                          Vec<tokenstream::TokenTree>) -> Box<MacResult+'cx>
+                          Vec<tokenstream::TokenTree>) -> Box<dyn MacResult+'cx>
 {
     fn expand<'cx>(&self,
                    cx: &'cx mut ExtCtxt,
                    sp: Span,
                    ident: ast::Ident,
                    token_tree: Vec<tokenstream::TokenTree>)
-                   -> Box<MacResult+'cx>
+                   -> Box<dyn MacResult+'cx>
     {
         (*self)(cx, sp, ident, token_tree)
     }
@@ -378,7 +379,7 @@ macro_rules! make_MacEager {
 
         impl MacEager {
             $(
-                pub fn $fld(v: $t) -> Box<MacResult> {
+                pub fn $fld(v: $t) -> Box<dyn MacResult> {
                     Box::new(MacEager {
                         $fld: Some(v),
                         ..Default::default()
@@ -462,7 +463,7 @@ impl DummyResult {
     ///
     /// Use this as a return value after hitting any errors and
     /// calling `span_err`.
-    pub fn any(sp: Span) -> Box<MacResult+'static> {
+    pub fn any(sp: Span) -> Box<dyn MacResult+'static> {
         Box::new(DummyResult { expr_only: false, span: sp })
     }
 
@@ -471,7 +472,7 @@ impl DummyResult {
     /// Use this for macros that must expand to an expression, so even
     /// if an error is encountered internally, the user will receive
     /// an error that they also used it in the wrong place.
-    pub fn expr(sp: Span) -> Box<MacResult+'static> {
+    pub fn expr(sp: Span) -> Box<dyn MacResult+'static> {
         Box::new(DummyResult { expr_only: true, span: sp })
     }
 
@@ -559,7 +560,7 @@ impl MacResult for DummyResult {
 }
 
 pub type BuiltinDeriveFn =
-    for<'cx> fn(&'cx mut ExtCtxt, Span, &MetaItem, &Annotatable, &mut FnMut(Annotatable));
+    for<'cx> fn(&'cx mut ExtCtxt, Span, &MetaItem, &Annotatable, &mut dyn FnMut(Annotatable));
 
 /// Represents different kinds of macro invocations that can be resolved.
 #[derive(Clone, Copy, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
@@ -590,15 +591,15 @@ pub enum SyntaxExtension {
     /// `#[derive(...)]` is a `MultiItemDecorator`.
     ///
     /// Prefer ProcMacro or MultiModifier since they are more flexible.
-    MultiDecorator(Box<MultiItemDecorator + sync::Sync + sync::Send>),
+    MultiDecorator(Box<dyn MultiItemDecorator + sync::Sync + sync::Send>),
 
     /// A syntax extension that is attached to an item and modifies it
     /// in-place. Also allows decoration, i.e., creating new items.
-    MultiModifier(Box<MultiItemModifier + sync::Sync + sync::Send>),
+    MultiModifier(Box<dyn MultiItemModifier + sync::Sync + sync::Send>),
 
     /// A function-like procedural macro. TokenStream -> TokenStream.
     ProcMacro {
-        expander: Box<ProcMacro + sync::Sync + sync::Send>,
+        expander: Box<dyn ProcMacro + sync::Sync + sync::Send>,
         allow_internal_unstable: bool,
         edition: Edition,
     },
@@ -607,13 +608,13 @@ pub enum SyntaxExtension {
     /// The first TokenSteam is the attribute, the second is the annotated item.
     /// Allows modification of the input items and adding new items, similar to
     /// MultiModifier, but uses TokenStreams, rather than AST nodes.
-    AttrProcMacro(Box<AttrProcMacro + sync::Sync + sync::Send>, Edition),
+    AttrProcMacro(Box<dyn AttrProcMacro + sync::Sync + sync::Send>, Edition),
 
     /// A normal, function-like syntax extension.
     ///
     /// `bytes!` is a `NormalTT`.
     NormalTT {
-        expander: Box<TTMacroExpander + sync::Sync + sync::Send>,
+        expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
         def_info: Option<(ast::NodeId, Span)>,
         /// Whether the contents of the macro can
         /// directly use `#[unstable]` things (true == yes).
@@ -633,13 +634,13 @@ pub enum SyntaxExtension {
     /// A function-like syntax extension that has an extra ident before
     /// the block.
     ///
-    IdentTT(Box<IdentMacroExpander + sync::Sync + sync::Send>, Option<Span>, bool),
+    IdentTT(Box<dyn IdentMacroExpander + sync::Sync + sync::Send>, Option<Span>, bool),
 
     /// An attribute-like procedural macro. TokenStream -> TokenStream.
     /// The input is the annotated item.
     /// Allows generating code to implement a Trait for a given struct
     /// or enum item.
-    ProcMacroDerive(Box<MultiItemModifier + sync::Sync + sync::Send>,
+    ProcMacroDerive(Box<dyn MultiItemModifier + sync::Sync + sync::Send>,
                     Vec<Symbol> /* inert attribute names */, Edition),
 
     /// An attribute-like procedural macro that derives a builtin trait.
@@ -647,7 +648,7 @@ pub enum SyntaxExtension {
 
     /// A declarative macro, e.g. `macro m() {}`.
     DeclMacro {
-        expander: Box<TTMacroExpander + sync::Sync + sync::Send>,
+        expander: Box<dyn TTMacroExpander + sync::Sync + sync::Send>,
         def_info: Option<(ast::NodeId, Span)>,
         is_transparent: bool,
         edition: Edition,
@@ -778,7 +779,7 @@ pub struct ExtCtxt<'a> {
     pub parse_sess: &'a parse::ParseSess,
     pub ecfg: expand::ExpansionConfig<'a>,
     pub root_path: PathBuf,
-    pub resolver: &'a mut Resolver,
+    pub resolver: &'a mut dyn Resolver,
     pub resolve_err_count: usize,
     pub current_expansion: ExpansionData,
     pub expansions: HashMap<Span, Vec<String>>,
@@ -787,7 +788,7 @@ pub struct ExtCtxt<'a> {
 impl<'a> ExtCtxt<'a> {
     pub fn new(parse_sess: &'a parse::ParseSess,
                ecfg: expand::ExpansionConfig<'a>,
-               resolver: &'a mut Resolver)
+               resolver: &'a mut dyn Resolver)
                -> ExtCtxt<'a> {
         ExtCtxt {
             parse_sess,
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index f29bff20f3d..865cb3d0d45 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -71,7 +71,7 @@ macro_rules! ast_fragments {
                 }
             }
 
-            fn make_from<'a>(self, result: Box<MacResult + 'a>) -> Option<AstFragment> {
+            fn make_from<'a>(self, result: Box<dyn MacResult + 'a>) -> Option<AstFragment> {
                 match self {
                     AstFragmentKind::OptExpr =>
                         result.make_expr().map(Some).map(AstFragment::OptExpr),
diff --git a/src/libsyntax/ext/quote.rs b/src/libsyntax/ext/quote.rs
index a6e6ccde72c..1ace4d4a880 100644
--- a/src/libsyntax/ext/quote.rs
+++ b/src/libsyntax/ext/quote.rs
@@ -452,7 +452,7 @@ pub fn parse_path_panic(parser: &mut Parser, mode: PathStyle) -> ast::Path {
 pub fn expand_quote_tokens<'cx>(cx: &'cx mut ExtCtxt,
                                 sp: Span,
                                 tts: &[TokenTree])
-                                -> Box<base::MacResult+'cx> {
+                                -> Box<dyn base::MacResult+'cx> {
     let (cx_expr, expr) = expand_tts(cx, sp, tts);
     let expanded = expand_wrapper(cx, sp, cx_expr, expr, &[&["syntax", "ext", "quote", "rt"]]);
     base::MacEager::expr(expanded)
@@ -461,7 +461,7 @@ pub fn expand_quote_tokens<'cx>(cx: &'cx mut ExtCtxt,
 pub fn expand_quote_expr<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[TokenTree])
-                              -> Box<base::MacResult+'cx> {
+                              -> Box<dyn base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_expr_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -469,7 +469,7 @@ pub fn expand_quote_expr<'cx>(cx: &'cx mut ExtCtxt,
 pub fn expand_quote_item<'cx>(cx: &'cx mut ExtCtxt,
                               sp: Span,
                               tts: &[TokenTree])
-                              -> Box<base::MacResult+'cx> {
+                              -> Box<dyn base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_item_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -477,7 +477,7 @@ pub fn expand_quote_item<'cx>(cx: &'cx mut ExtCtxt,
 pub fn expand_quote_pat<'cx>(cx: &'cx mut ExtCtxt,
                              sp: Span,
                              tts: &[TokenTree])
-                             -> Box<base::MacResult+'cx> {
+                             -> Box<dyn base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_pat_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -485,7 +485,7 @@ pub fn expand_quote_pat<'cx>(cx: &'cx mut ExtCtxt,
 pub fn expand_quote_arm(cx: &mut ExtCtxt,
                         sp: Span,
                         tts: &[TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_arm_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -493,7 +493,7 @@ pub fn expand_quote_arm(cx: &mut ExtCtxt,
 pub fn expand_quote_ty(cx: &mut ExtCtxt,
                        sp: Span,
                        tts: &[TokenTree])
-                       -> Box<base::MacResult+'static> {
+                       -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_ty_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -501,7 +501,7 @@ pub fn expand_quote_ty(cx: &mut ExtCtxt,
 pub fn expand_quote_stmt(cx: &mut ExtCtxt,
                          sp: Span,
                          tts: &[TokenTree])
-                         -> Box<base::MacResult+'static> {
+                         -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_stmt_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -509,7 +509,7 @@ pub fn expand_quote_stmt(cx: &mut ExtCtxt,
 pub fn expand_quote_attr(cx: &mut ExtCtxt,
                          sp: Span,
                          tts: &[TokenTree])
-                         -> Box<base::MacResult+'static> {
+                         -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_attribute_panic",
                                     vec![cx.expr_bool(sp, true)], tts);
 
@@ -519,7 +519,7 @@ pub fn expand_quote_attr(cx: &mut ExtCtxt,
 pub fn expand_quote_arg(cx: &mut ExtCtxt,
                         sp: Span,
                         tts: &[TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_arg_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -527,7 +527,7 @@ pub fn expand_quote_arg(cx: &mut ExtCtxt,
 pub fn expand_quote_block(cx: &mut ExtCtxt,
                         sp: Span,
                         tts: &[TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_block_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -535,7 +535,7 @@ pub fn expand_quote_block(cx: &mut ExtCtxt,
 pub fn expand_quote_meta_item(cx: &mut ExtCtxt,
                         sp: Span,
                         tts: &[TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_meta_item_panic", vec![], tts);
     base::MacEager::expr(expanded)
 }
@@ -543,7 +543,7 @@ pub fn expand_quote_meta_item(cx: &mut ExtCtxt,
 pub fn expand_quote_path(cx: &mut ExtCtxt,
                         sp: Span,
                         tts: &[TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let mode = mk_parser_path(cx, sp, &["PathStyle", "Type"]);
     let expanded = expand_parse_call(cx, sp, "parse_path_panic", vec![mode], tts);
     base::MacEager::expr(expanded)
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 669536f519c..0c36c072a03 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -32,7 +32,7 @@ use rustc_data_structures::sync::Lrc;
 
 /// line!(): expands to the current line number
 pub fn expand_line(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                   -> Box<base::MacResult+'static> {
+                   -> Box<dyn base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "line!");
 
     let topmost = cx.expansion_cause().unwrap_or(sp);
@@ -43,7 +43,7 @@ pub fn expand_line(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
 
 /* column!(): expands to the current column number */
 pub fn expand_column(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<base::MacResult+'static> {
+                  -> Box<dyn base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "column!");
 
     let topmost = cx.expansion_cause().unwrap_or(sp);
@@ -54,7 +54,7 @@ pub fn expand_column(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
 
 /* __rust_unstable_column!(): expands to the current column number */
 pub fn expand_column_gated(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<base::MacResult+'static> {
+                  -> Box<dyn base::MacResult+'static> {
     if sp.allows_unstable() {
         expand_column(cx, sp, tts)
     } else {
@@ -66,7 +66,7 @@ pub fn expand_column_gated(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::Token
 /// The filemap (`loc.file`) contains a bunch more information we could spit
 /// out if we wanted.
 pub fn expand_file(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                   -> Box<base::MacResult+'static> {
+                   -> Box<dyn base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "file!");
 
     let topmost = cx.expansion_cause().unwrap_or(sp);
@@ -75,13 +75,13 @@ pub fn expand_file(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
 }
 
 pub fn expand_stringify(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                        -> Box<base::MacResult+'static> {
+                        -> Box<dyn base::MacResult+'static> {
     let s = pprust::tts_to_string(tts);
     base::MacEager::expr(cx.expr_str(sp, Symbol::intern(&s)))
 }
 
 pub fn expand_mod(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                  -> Box<base::MacResult+'static> {
+                  -> Box<dyn base::MacResult+'static> {
     base::check_zero_tts(cx, sp, tts, "module_path!");
     let mod_path = &cx.current_expansion.module.mod_path;
     let string = mod_path.iter().map(|x| x.to_string()).collect::<Vec<String>>().join("::");
@@ -93,7 +93,7 @@ pub fn expand_mod(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
 /// This is generally a bad idea because it's going to behave
 /// unhygienically.
 pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                           -> Box<base::MacResult+'cx> {
+                           -> Box<dyn base::MacResult+'cx> {
     let file = match get_single_str_from_tts(cx, sp, tts, "include!") {
         Some(f) => f,
         None => return DummyResult::expr(sp),
@@ -131,7 +131,7 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[tokenstream::T
 
 // include_str! : read the given file, insert it as a literal string expr
 pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                          -> Box<base::MacResult+'static> {
+                          -> Box<dyn base::MacResult+'static> {
     let file = match get_single_str_from_tts(cx, sp, tts, "include_str!") {
         Some(f) => f,
         None => return DummyResult::expr(sp)
@@ -168,7 +168,7 @@ pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenT
 }
 
 pub fn expand_include_bytes(cx: &mut ExtCtxt, sp: Span, tts: &[tokenstream::TokenTree])
-                            -> Box<base::MacResult+'static> {
+                            -> Box<dyn base::MacResult+'static> {
     let file = match get_single_str_from_tts(cx, sp, tts, "include_bytes!") {
         Some(f) => f,
         None => return DummyResult::expr(sp)
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 70fc9dada42..9ebead1062e 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -73,7 +73,7 @@ impl TTMacroExpander for MacroRulesMacroExpander {
                    cx: &'cx mut ExtCtxt,
                    sp: Span,
                    input: TokenStream)
-                   -> Box<MacResult+'cx> {
+                   -> Box<dyn MacResult+'cx> {
         if !self.valid {
             return DummyResult::any(sp);
         }
@@ -99,7 +99,7 @@ fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
                           arg: TokenStream,
                           lhses: &[quoted::TokenTree],
                           rhses: &[quoted::TokenTree])
-                          -> Box<MacResult+'cx> {
+                          -> Box<dyn MacResult+'cx> {
     if cx.trace_macros() {
         trace_macros_note(cx, sp, format!("expanding `{}! {{ {} }}`", name, arg));
     }
diff --git a/src/libsyntax/json.rs b/src/libsyntax/json.rs
index f129aea32b8..65de1503966 100644
--- a/src/libsyntax/json.rs
+++ b/src/libsyntax/json.rs
@@ -34,9 +34,9 @@ use std::sync::{Arc, Mutex};
 use rustc_serialize::json::{as_json, as_pretty_json};
 
 pub struct JsonEmitter {
-    dst: Box<Write + Send>,
+    dst: Box<dyn Write + Send>,
     registry: Option<Registry>,
-    cm: Lrc<CodeMapper + sync::Send + sync::Sync>,
+    cm: Lrc<dyn CodeMapper + sync::Send + sync::Sync>,
     pretty: bool,
     ui_testing: bool,
 }
@@ -60,7 +60,7 @@ impl JsonEmitter {
                             pretty)
     }
 
-    pub fn new(dst: Box<Write + Send>,
+    pub fn new(dst: Box<dyn Write + Send>,
                registry: Option<Registry>,
                code_map: Lrc<CodeMap>,
                pretty: bool) -> JsonEmitter {
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index 1ace9193dc6..ffaad9bf94c 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -14,6 +14,8 @@
 //!
 //! This API is completely unstable and subject to change.
 
+#![deny(bare_trait_objects)]
+
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
diff --git a/src/libsyntax/parse/lexer/comments.rs b/src/libsyntax/parse/lexer/comments.rs
index 3995a9b8689..20a585b6601 100644
--- a/src/libsyntax/parse/lexer/comments.rs
+++ b/src/libsyntax/parse/lexer/comments.rs
@@ -357,7 +357,7 @@ pub struct Literal {
 
 // it appears this function is called only from pprust... that's
 // probably not a good thing.
-pub fn gather_comments_and_literals(sess: &ParseSess, path: FileName, srdr: &mut Read)
+pub fn gather_comments_and_literals(sess: &ParseSess, path: FileName, srdr: &mut dyn Read)
                                     -> (Vec<Comment>, Vec<Literal>) {
     let mut src = Vec::new();
     srdr.read_to_end(&mut src).unwrap();
diff --git a/src/libsyntax/print/pp.rs b/src/libsyntax/print/pp.rs
index e7bd369053c..086de35d531 100644
--- a/src/libsyntax/print/pp.rs
+++ b/src/libsyntax/print/pp.rs
@@ -241,7 +241,7 @@ pub struct PrintStackElem {
 
 const SIZE_INFINITY: isize = 0xffff;
 
-pub fn mk_printer<'a>(out: Box<io::Write+'a>, linewidth: usize) -> Printer<'a> {
+pub fn mk_printer<'a>(out: Box<dyn io::Write+'a>, linewidth: usize) -> Printer<'a> {
     // Yes 55, it makes the ring buffers big enough to never fall behind.
     let n: usize = 55 * linewidth;
     debug!("mk_printer {}", linewidth);
@@ -264,7 +264,7 @@ pub fn mk_printer<'a>(out: Box<io::Write+'a>, linewidth: usize) -> Printer<'a> {
 }
 
 pub struct Printer<'a> {
-    out: Box<io::Write+'a>,
+    out: Box<dyn io::Write+'a>,
     buf_max_len: usize,
     /// Width of lines we're constrained to
     margin: isize,
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 74edf538842..c5ba7daaeb8 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -62,10 +62,10 @@ pub struct State<'a> {
     literals: Peekable<vec::IntoIter<comments::Literal>>,
     cur_cmnt: usize,
     boxes: Vec<pp::Breaks>,
-    ann: &'a (PpAnn+'a),
+    ann: &'a (dyn PpAnn+'a),
 }
 
-fn rust_printer<'a>(writer: Box<Write+'a>, ann: &'a PpAnn) -> State<'a> {
+fn rust_printer<'a>(writer: Box<dyn Write+'a>, ann: &'a dyn PpAnn) -> State<'a> {
     State {
         s: pp::mk_printer(writer, DEFAULT_COLUMNS),
         cm: None,
@@ -88,9 +88,9 @@ pub fn print_crate<'a>(cm: &'a CodeMap,
                        sess: &ParseSess,
                        krate: &ast::Crate,
                        filename: FileName,
-                       input: &mut Read,
-                       out: Box<Write+'a>,
-                       ann: &'a PpAnn,
+                       input: &mut dyn Read,
+                       out: Box<dyn Write+'a>,
+                       ann: &'a dyn PpAnn,
                        is_expanded: bool) -> io::Result<()> {
     let mut s = State::new_from_input(cm, sess, filename, input, out, ann, is_expanded);
 
@@ -121,9 +121,9 @@ impl<'a> State<'a> {
     pub fn new_from_input(cm: &'a CodeMap,
                           sess: &ParseSess,
                           filename: FileName,
-                          input: &mut Read,
-                          out: Box<Write+'a>,
-                          ann: &'a PpAnn,
+                          input: &mut dyn Read,
+                          out: Box<dyn Write+'a>,
+                          ann: &'a dyn PpAnn,
                           is_expanded: bool) -> State<'a> {
         let (cmnts, lits) = comments::gather_comments_and_literals(sess, filename, input);
 
@@ -139,8 +139,8 @@ impl<'a> State<'a> {
     }
 
     pub fn new(cm: &'a CodeMap,
-               out: Box<Write+'a>,
-               ann: &'a PpAnn,
+               out: Box<dyn Write+'a>,
+               ann: &'a dyn PpAnn,
                comments: Option<Vec<comments::Comment>>,
                literals: Option<Vec<comments::Literal>>) -> State<'a> {
         State {
diff --git a/src/libsyntax/test.rs b/src/libsyntax/test.rs
index 51fbe34028e..4d5b0b327dd 100644
--- a/src/libsyntax/test.rs
+++ b/src/libsyntax/test.rs
@@ -72,7 +72,7 @@ struct TestCtxt<'a> {
 // Traverse the crate, collecting all the test functions, eliding any
 // existing main functions, and synthesizing a main test harness
 pub fn modify_for_testing(sess: &ParseSess,
-                          resolver: &mut Resolver,
+                          resolver: &mut dyn Resolver,
                           should_test: bool,
                           krate: ast::Crate,
                           span_diagnostic: &errors::Handler,
@@ -278,7 +278,7 @@ fn mk_reexport_mod(cx: &mut TestCtxt,
 }
 
 fn generate_test_harness(sess: &ParseSess,
-                         resolver: &mut Resolver,
+                         resolver: &mut dyn Resolver,
                          reexport_test_harness_main: Option<Symbol>,
                          krate: ast::Crate,
                          sd: &errors::Handler,