Rollup merge of rust-lang#41520 - estebank:trace-macro, r=nikomatsakis

Use diagnostics for trace_macro instead of println

When using `trace_macro`, use `span_label`s instead of `println`:

```rust
note: trace_macro
  --> $DIR/trace-macro.rs:14:5
   |
14 |     println!("Hello, World!");
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: expands to `println! { "Hello, World!" }`
   = note: expands to `print! { concat ! ( "Hello, World!" , "\n" ) }`
```

Fix rust-lang#22597.

src/librustc_errors/lib.rs

@@ -388,6 +388,14 @@ impl Handler {
     pub fn span_note_without_error<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
         self.emit(&sp.into(), msg, Note);
     }
+    pub fn span_note_diag<'a>(&'a self,
+                              sp: Span,
+                              msg: &str)
+                              -> DiagnosticBuilder<'a> {
+        let mut db = DiagnosticBuilder::new(self, Note, msg);
+        db.set_span(sp);
+        db
+    }
     pub fn span_unimpl<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
         self.span_bug(sp, &format!("unimplemented {}", msg));
     }

src/libsyntax/ext/base.rs

@@ -24,6 +24,7 @@ use ptr::P;
 use symbol::Symbol;
 use util::small_vector::SmallVector;
 
+use std::collections::HashMap;
 use std::path::PathBuf;
 use std::rc::Rc;
 use std::default::Default;
@@ -643,6 +644,7 @@ pub struct ExtCtxt<'a> {
     pub resolver: &'a mut Resolver,
     pub resolve_err_count: usize,
     pub current_expansion: ExpansionData,
+    pub expansions: HashMap<Span, Vec<String>>,
 }
 
 impl<'a> ExtCtxt<'a> {
@@ -662,6 +664,7 @@ impl<'a> ExtCtxt<'a> {
                 module: Rc::new(ModuleData { mod_path: Vec::new(), directory: PathBuf::new() }),
                 directory_ownership: DirectoryOwnership::Owned,
             },
+            expansions: HashMap::new(),
         }
     }
 
@@ -765,6 +768,15 @@ impl<'a> ExtCtxt<'a> {
     pub fn span_bug(&self, sp: Span, msg: &str) -> ! {
         self.parse_sess.span_diagnostic.span_bug(sp, msg);
     }
+    pub fn trace_macros_diag(&self) {
+        for (sp, notes) in self.expansions.iter() {
+            let mut db = self.parse_sess.span_diagnostic.span_note_diag(*sp, &"trace_macro");
+            for note in notes {
+                db.note(&note);
+            }
+            db.emit();
+        }
+    }
     pub fn bug(&self, msg: &str) -> ! {
         self.parse_sess.span_diagnostic.bug(msg);
     }

src/libsyntax/ext/expand.rs

@@ -231,7 +231,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             },
             _ => unreachable!(),
         };
-
+        self.cx.trace_macros_diag();
         krate
     }
 

src/libsyntax/ext/tt/macro_rules.rs

@@ -27,8 +27,8 @@ use symbol::Symbol;
 use tokenstream::{TokenStream, TokenTree};
 
 use std::cell::RefCell;
-use std::collections::{HashMap};
-use std::collections::hash_map::{Entry};
+use std::collections::HashMap;
+use std::collections::hash_map::Entry;
 use std::rc::Rc;
 
 pub struct ParserAnyMacro<'a> {
@@ -85,15 +85,17 @@ impl TTMacroExpander for MacroRulesMacroExpander {
 }
 
 /// Given `lhses` and `rhses`, this is the new macro we create
-fn generic_extension<'cx>(cx: &'cx ExtCtxt,
+fn generic_extension<'cx>(cx: &'cx mut ExtCtxt,
                           sp: Span,
                           name: ast::Ident,
                           arg: TokenStream,
                           lhses: &[quoted::TokenTree],
                           rhses: &[quoted::TokenTree])
                           -> Box<MacResult+'cx> {
     if cx.trace_macros() {
-        println!("{}! {{ {} }}", name, arg);
+        let sp = sp.macro_backtrace().last().map(|trace| trace.call_site).unwrap_or(sp);
+        let mut values: &mut Vec<String> = cx.expansions.entry(sp).or_insert(vec![]);
+        values.push(format!("expands to `{}! {{ {} }}`", name, arg));
     }
 
     // Which arm's failure should we report? (the one furthest along)

src/test/run-make/trace-macros-flag/hello.rs → src/test/ui/macros/trace-macro.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-flags: -Z trace-macros
+
 fn main() {
     println!("Hello, World!");
 }

src/test/ui/macros/trace-macro.stderr

@@ -0,0 +1,9 @@
+note: trace_macro
+  --> $DIR/trace-macro.rs:14:5
+   |
+14 |     println!("Hello, World!");
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: expands to `println! { "Hello, World!" }`
+   = note: expands to `print! { concat ! ( "Hello, World!" , "/n" ) }`
+