Avoid returning original macro if expansion fails.

Closes #11692. Instead of returning the original expression, a dummy expression
(with identical span) is returned. This prevents infinite loops of failed
expansions as well as odd double error messages in certain situations.

10 files changed, 34 insertions, 28 deletions

diff --git a/src/libsyntax/ext/asm.rs b/src/libsyntax/ext/asm.rs
index 1a3ebf3ce5d..1bf82573c49 100644
--- a/src/libsyntax/ext/asm.rs
+++ b/src/libsyntax/ext/asm.rs
@@ -64,7 +64,7 @@ pub fn expand_asm(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                                                    "inline assembly must be a string literal.") {
                     Some((s, st)) => (s, st),
                     // let compilation continue
-                    None => return MacResult::dummy_expr(),
+                    None => return MacResult::dummy_expr(sp),
                 };
                 asm = s;
                 asm_str_style = Some(style);
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 3dac82ae3b7..e6fffe8b53f 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -101,6 +101,7 @@ pub trait AnyMacro {
     fn make_stmt(&self) -> @ast::Stmt;
 }
 
+
 pub enum MacResult {
     MRExpr(@ast::Expr),
     MRItem(@ast::Item),
@@ -112,10 +113,15 @@ impl MacResult {
     /// type signatures after emitting a non-fatal error (which stop
     /// compilation well before the validity (or otherwise)) of the
     /// expression are checked.
-    pub fn dummy_expr() -> MacResult {
-        MRExpr(@ast::Expr {
-                id: ast::DUMMY_NODE_ID, node: ast::ExprLogLevel, span: codemap::DUMMY_SP
-            })
+    pub fn raw_dummy_expr(sp: codemap::Span) -> @ast::Expr {
+        @ast::Expr {
+            id: ast::DUMMY_NODE_ID,
+            node: ast::ExprLogLevel,
+            span: sp
+        }
+    }
+    pub fn dummy_expr(sp: codemap::Span) -> MacResult {
+        MRExpr(MacResult::raw_dummy_expr(sp))
     }
 }
 
diff --git a/src/libsyntax/ext/bytes.rs b/src/libsyntax/ext/bytes.rs
index 39bb870b969..68aa757c524 100644
--- a/src/libsyntax/ext/bytes.rs
+++ b/src/libsyntax/ext/bytes.rs
@@ -21,7 +21,7 @@ use std::char;
 pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]) -> base::MacResult {
     // Gather all argument expressions
     let exprs = match get_exprs_from_tts(cx, sp, tts) {
-        None => return MacResult::dummy_expr(),
+        None => return MacResult::dummy_expr(sp),
         Some(e) => e,
     };
     let mut bytes = ~[];
diff --git a/src/libsyntax/ext/concat.rs b/src/libsyntax/ext/concat.rs
index c13f9bf92af..5316b8f7212 100644
--- a/src/libsyntax/ext/concat.rs
+++ b/src/libsyntax/ext/concat.rs
@@ -21,7 +21,7 @@ pub fn expand_syntax_ext(cx: &mut base::ExtCtxt,
                          tts: &[ast::TokenTree]) -> base::MacResult {
     let es = match base::get_exprs_from_tts(cx, sp, tts) {
         Some(e) => e,
-        None => return base::MacResult::dummy_expr()
+        None => return base::MacResult::dummy_expr(sp)
     };
     let mut accumulator = ~"";
     for e in es.move_iter() {
diff --git a/src/libsyntax/ext/concat_idents.rs b/src/libsyntax/ext/concat_idents.rs
index 15e9d31daa0..85cfd4f61e4 100644
--- a/src/libsyntax/ext/concat_idents.rs
+++ b/src/libsyntax/ext/concat_idents.rs
@@ -25,7 +25,7 @@ pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                 ast::TTTok(_, token::COMMA) => (),
                 _ => {
                     cx.span_err(sp, "concat_idents! expecting comma.");
-                    return MacResult::dummy_expr();
+                    return MacResult::dummy_expr(sp);
                 }
             }
         } else {
@@ -35,7 +35,7 @@ pub fn expand_syntax_ext(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                 }
                 _ => {
                     cx.span_err(sp, "concat_idents! requires ident args.");
-                    return MacResult::dummy_expr();
+                    return MacResult::dummy_expr(sp);
                 }
             }
         }
diff --git a/src/libsyntax/ext/env.rs b/src/libsyntax/ext/env.rs
index c23a1ce1e28..fec1e70af07 100644
--- a/src/libsyntax/ext/env.rs
+++ b/src/libsyntax/ext/env.rs
@@ -26,7 +26,7 @@ use std::os;
 pub fn expand_option_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     -> base::MacResult {
     let var = match get_single_str_from_tts(cx, sp, tts, "option_env!") {
-        None => return MacResult::dummy_expr(),
+        None => return MacResult::dummy_expr(sp),
         Some(v) => v
     };
 
@@ -42,14 +42,14 @@ pub fn expand_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     let exprs = match get_exprs_from_tts(cx, sp, tts) {
         Some([]) => {
             cx.span_err(sp, "env! takes 1 or 2 arguments");
-            return MacResult::dummy_expr();
+            return MacResult::dummy_expr(sp);
         }
-        None => return MacResult::dummy_expr(),
+        None => return MacResult::dummy_expr(sp),
         Some(exprs) => exprs
     };
 
     let var = match expr_to_str(cx, exprs[0], "expected string literal") {
-        None => return MacResult::dummy_expr(),
+        None => return MacResult::dummy_expr(sp),
         Some((v, _style)) => v
     };
     let msg = match exprs.len() {
@@ -60,13 +60,13 @@ pub fn expand_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         }
         2 => {
             match expr_to_str(cx, exprs[1], "expected string literal") {
-                None => return MacResult::dummy_expr(),
+                None => return MacResult::dummy_expr(sp),
                 Some((s, _style)) => s
             }
         }
         _ => {
             cx.span_err(sp, "env! takes 1 or 2 arguments");
-            return MacResult::dummy_expr();
+            return MacResult::dummy_expr(sp);
         }
     };
 
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 97766e1a14b..4b81713f7d0 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -51,7 +51,7 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
                             format!("expected macro name without module \
                                   separators"));
                         // let compilation continue
-                        return e;
+                        return MacResult::raw_dummy_expr(e.span);
                     }
                     let extname = pth.segments[0].identifier;
                     let extnamestr = token::get_ident(extname);
@@ -64,7 +64,7 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
                                         extnamestr.get()));
 
                             // let compilation continue
-                            return e;
+                            return MacResult::raw_dummy_expr(e.span);
                         }
                         Some(&NormalTT(ref expandfun, exp_span)) => {
                             fld.cx.bt_push(ExpnInfo {
@@ -98,7 +98,7 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
                                             extnamestr.get()
                                         )
                                     );
-                                    return e;
+                                    return MacResult::raw_dummy_expr(e.span);
                                 }
                             };
 
@@ -111,7 +111,7 @@ pub fn expand_expr(e: @ast::Expr, fld: &mut MacroExpander) -> @ast::Expr {
                                 format!("'{}' is not a tt-style macro",
                                         extnamestr.get())
                             );
-                            return e;
+                            return MacResult::raw_dummy_expr(e.span);
                         }
                     };
 
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 01d348595b8..13b1afb4c00 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -811,7 +811,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt, sp: Span,
                                 expr,
                                 "format argument must be a string literal.") {
         Some((fmt, _)) => fmt,
-        None => return efmt
+        None => return MacResult::raw_dummy_expr(sp)
     };
 
     let mut parser = parse::Parser::new(fmt.get());
@@ -829,7 +829,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt, sp: Span,
     match parser.errors.shift() {
         Some(error) => {
             cx.ecx.span_err(efmt.span, "invalid format string: " + error);
-            return efmt;
+            return MacResult::raw_dummy_expr(sp);
         }
         None => {}
     }
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 150f054b2af..c81ee55c237 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -83,7 +83,7 @@ pub fn expand_include(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     -> base::MacResult {
     let file = match get_single_str_from_tts(cx, sp, tts, "include!") {
         Some(f) => f,
-        None => return MacResult::dummy_expr(),
+        None => return MacResult::dummy_expr(sp),
     };
     // The file will be added to the code map by the parser
     let mut p =
@@ -101,13 +101,13 @@ pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     -> base::MacResult {
     let file = match get_single_str_from_tts(cx, sp, tts, "include_str!") {
         Some(f) => f,
-        None => return MacResult::dummy_expr()
+        None => return MacResult::dummy_expr(sp)
     };
     let file = res_rel_file(cx, sp, &Path::new(file));
     let bytes = match File::open(&file).read_to_end() {
         Err(e) => {
             cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
-            return MacResult::dummy_expr();
+            return MacResult::dummy_expr(sp);
         }
         Ok(bytes) => bytes,
     };
@@ -123,7 +123,7 @@ pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         }
         None => {
             cx.span_err(sp, format!("{} wasn't a utf-8 file", file.display()));
-            return MacResult::dummy_expr();
+            return MacResult::dummy_expr(sp);
         }
     }
 }
@@ -133,13 +133,13 @@ pub fn expand_include_bin(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
 {
     let file = match get_single_str_from_tts(cx, sp, tts, "include_bin!") {
         Some(f) => f,
-        None => return MacResult::dummy_expr()
+        None => return MacResult::dummy_expr(sp)
     };
     let file = res_rel_file(cx, sp, &Path::new(file));
     match File::open(&file).read_to_end() {
         Err(e) => {
             cx.span_err(sp, format!("couldn't read {}: {}", file.display(), e));
-            return MacResult::dummy_expr();
+            return MacResult::dummy_expr(sp);
         }
         Ok(bytes) => {
             base::MRExpr(cx.expr_lit(sp, ast::LitBinary(Rc::new(bytes))))
diff --git a/src/libsyntax/ext/trace_macros.rs b/src/libsyntax/ext/trace_macros.rs
index 4189ea6a967..db2c9dcddb6 100644
--- a/src/libsyntax/ext/trace_macros.rs
+++ b/src/libsyntax/ext/trace_macros.rs
@@ -33,7 +33,7 @@ pub fn expand_trace_macros(cx: &mut ExtCtxt,
         cx.set_trace_macros(false);
     } else {
         cx.span_err(sp, "trace_macros! only accepts `true` or `false`");
-        return base::MacResult::dummy_expr();
+        return base::MacResult::dummy_expr(sp);
     }
 
     rust_parser.bump();