Fix trace_macros and log_syntax

src/libsyntax/ext/base.rs

@@ -456,7 +456,8 @@ impl MacResult for MacEager {
 #[derive(Copy, Clone)]
 pub struct DummyResult {
     expr_only: bool,
-    span: Span
+    is_error: bool,
+    span: Span,
 }
 
 impl DummyResult {
@@ -464,8 +465,13 @@ impl DummyResult {
     ///
     /// Use this as a return value after hitting any errors and
     /// calling `span_err`.
-    pub fn any(sp: Span) -> Box<dyn MacResult+'static> {
+    pub fn any(span: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: false, span: sp })
+        Box::new(DummyResult { expr_only: false, is_error: true, span })
+    }
+
+    /// Same as `any`, but must be a valid fragment, not error.
+    pub fn any_valid(span: Span) -> Box<dyn MacResult+'static> {
+        Box::new(DummyResult { expr_only: false, is_error: false, span })
     }
 
     /// Create a default MacResult that can only be an expression.
@@ -473,15 +479,15 @@ 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<dyn MacResult+'static> {
+    pub fn expr(span: Span) -> Box<dyn MacResult+'static> {
-        Box::new(DummyResult { expr_only: true, span: sp })
+        Box::new(DummyResult { expr_only: true, is_error: true, span })
     }
 
     /// A plain dummy expression.
-    pub fn raw_expr(sp: Span) -> P<ast::Expr> {
+    pub fn raw_expr(sp: Span, is_error: bool) -> P<ast::Expr> {
         P(ast::Expr {
             id: ast::DUMMY_NODE_ID,
-            node: ast::ExprKind::Err,
+            node: if is_error { ast::ExprKind::Err } else { ast::ExprKind::Tup(Vec::new()) },
             span: sp,
             attrs: ThinVec::new(),
         })
@@ -497,10 +503,10 @@ impl DummyResult {
     }
 
     /// A plain dummy type.
-    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
+    pub fn raw_ty(sp: Span, is_error: bool) -> P<ast::Ty> {
         P(ast::Ty {
             id: ast::DUMMY_NODE_ID,
-            node: ast::TyKind::Err,
+            node: if is_error { ast::TyKind::Err } else { ast::TyKind::Tup(Vec::new()) },
             span: sp
         })
     }
@@ -508,7 +514,7 @@ impl DummyResult {
 
 impl MacResult for DummyResult {
     fn make_expr(self: Box<DummyResult>) -> Option<P<ast::Expr>> {
-        Some(DummyResult::raw_expr(self.span))
+        Some(DummyResult::raw_expr(self.span, self.is_error))
     }
 
     fn make_pat(self: Box<DummyResult>) -> Option<P<ast::Pat>> {
@@ -551,13 +557,13 @@ impl MacResult for DummyResult {
     fn make_stmts(self: Box<DummyResult>) -> Option<SmallVec<[ast::Stmt; 1]>> {
         Some(smallvec![ast::Stmt {
             id: ast::DUMMY_NODE_ID,
-            node: ast::StmtKind::Expr(DummyResult::raw_expr(self.span)),
+            node: ast::StmtKind::Expr(DummyResult::raw_expr(self.span, self.is_error)),
             span: self.span,
         }])
     }
 
     fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
-        Some(DummyResult::raw_ty(self.span))
+        Some(DummyResult::raw_ty(self.span, self.is_error))
     }
 }
 

src/libsyntax/parse/parser.rs

@@ -4974,7 +4974,7 @@ impl<'a> Parser<'a> {
                     self.recover_stmt_(SemiColonMode::Ignore, BlockMode::Ignore);
                     Some(Stmt {
                         id: ast::DUMMY_NODE_ID,
-                        node: StmtKind::Expr(DummyResult::raw_expr(self.span)),
+                        node: StmtKind::Expr(DummyResult::raw_expr(self.span, true)),
                         span: self.span,
                     })
                 }

src/libsyntax_ext/deriving/default.rs

@@ -69,7 +69,7 @@ fn default_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructur
             span_err!(cx, trait_span, E0665,
                       "`Default` cannot be derived for enums, only structs");
             // let compilation continue
-            DummyResult::raw_expr(trait_span)
+            DummyResult::raw_expr(trait_span, true)
         }
         _ => cx.span_bug(trait_span, "Non-static method in `derive(Default)`"),
     };

src/libsyntax_ext/format.rs

@@ -666,7 +666,7 @@ impl<'a, 'b> Context<'a, 'b> {
                     "X" => "UpperHex",
                     _ => {
                         ecx.span_err(sp, &format!("unknown format trait `{}`", *tyname));
-                        return DummyResult::raw_expr(sp);
+                        return DummyResult::raw_expr(sp, true);
                     }
                 }
             }
@@ -761,7 +761,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt,
                 Applicability::MaybeIncorrect,
             );
             err.emit();
-            return DummyResult::raw_expr(sp);
+            return DummyResult::raw_expr(sp, true);
         }
     };
 
@@ -857,7 +857,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt,
             e.span_label(sp, label);
         }
         e.emit();
-        return DummyResult::raw_expr(sp);
+        return DummyResult::raw_expr(sp, true);
     }
 
     let arg_spans = parser.arg_places.iter()

src/libsyntax_ext/log_syntax.rs

@@ -20,5 +20,5 @@ pub fn expand_syntax_ext<'cx>(cx: &'cx mut base::ExtCtxt,
     println!("{}", print::pprust::tts_to_string(tts));
 
     // any so that `log_syntax` can be invoked as an expression and item.
-    base::DummyResult::any(sp)
+    base::DummyResult::any_valid(sp)
 }

src/libsyntax_ext/trace_macros.rs

@@ -28,5 +28,5 @@ pub fn expand_trace_macros(cx: &mut ExtCtxt,
         _ => cx.span_err(sp, "trace_macros! accepts only `true` or `false`"),
     }
 
-    base::DummyResult::any(sp)
+    base::DummyResult::any_valid(sp)
 }