Address the other cases of #22234; fix #22234.

The other cases: `concat_idents!`, `log_syntax!`, and `trace_macros!`,
(these macros, with `asm!`, are handled (eagerly) in feature_gate.rs).

src/libsyntax/ext/concat_idents.rs

@@ -12,12 +12,21 @@ use ast;
 use codemap::Span;
 use ext::base::*;
 use ext::base;
+use feature_gate;
 use parse::token;
 use parse::token::{str_to_ident};
 use ptr::P;
 
 pub fn expand_syntax_ext<'cx>(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                               -> Box<base::MacResult+'cx> {
+    if !cx.ecfg.enable_concat_idents() {
+        feature_gate::emit_feature_err(&cx.parse_sess.span_diagnostic,
+                                       "concat_idents",
+                                       sp,
+                                       feature_gate::EXPLAIN_CONCAT_IDENTS);
+        return base::DummyResult::expr(sp);
+    }
+
     let mut res_str = String::new();
     for (i, e) in tts.iter().enumerate() {
         if i & 1 == 1 {

src/libsyntax/ext/expand.rs

@@ -1436,6 +1436,27 @@ impl<'feat> ExpansionConfig<'feat> {
             _ => false,
         }
     }
+
+    pub fn enable_log_syntax(&self) -> bool {
+        match self.features {
+            Some(&Features { allow_log_syntax: true, .. }) => true,
+            _ => false,
+        }
+    }
+
+    pub fn enable_concat_idents(&self) -> bool {
+        match self.features {
+            Some(&Features { allow_concat_idents: true, .. }) => true,
+            _ => false,
+        }
+    }
+
+    pub fn enable_trace_macros(&self) -> bool {
+        match self.features {
+            Some(&Features { allow_trace_macros: true, .. }) => true,
+            _ => false,
+        }
+    }
 }
 
 pub fn expand_crate<'feat>(parse_sess: &parse::ParseSess,

src/libsyntax/ext/log_syntax.rs

@@ -11,12 +11,20 @@
 use ast;
 use codemap;
 use ext::base;
+use feature_gate;
 use print;
 
 pub fn expand_syntax_ext<'cx>(cx: &'cx mut base::ExtCtxt,
                               sp: codemap::Span,
                               tts: &[ast::TokenTree])
                               -> Box<base::MacResult+'cx> {
+    if !cx.ecfg.enable_log_syntax() {
+        feature_gate::emit_feature_err(&cx.parse_sess.span_diagnostic,
+                                       "log_syntax",
+                                       sp,
+                                       feature_gate::EXPLAIN_LOG_SYNTAX);
+        return base::DummyResult::any(sp);
+    }
 
     cx.print_backtrace();
 

src/libsyntax/ext/trace_macros.rs

@@ -12,6 +12,7 @@ use ast;
 use codemap::Span;
 use ext::base::ExtCtxt;
 use ext::base;
+use feature_gate;
 use parse::token::keywords;
 
 
@@ -19,6 +20,15 @@ pub fn expand_trace_macros(cx: &mut ExtCtxt,
                            sp: Span,
                            tt: &[ast::TokenTree])
                            -> Box<base::MacResult+'static> {
+    if !cx.ecfg.enable_trace_macros() {
+        feature_gate::emit_feature_err(&cx.parse_sess.span_diagnostic,
+                                       "trace_macros",
+                                       sp,
+                                       feature_gate::EXPLAIN_TRACE_MACROS);
+        return base::DummyResult::any(sp);
+    }
+
+
     match tt {
         [ast::TtToken(_, ref tok)] if tok.is_keyword(keywords::True) => {
             cx.set_trace_macros(true);