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trace_macros output should use span_note? #22597

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kmcallister opened this issue Feb 20, 2015 · 2 comments
Closed

trace_macros output should use span_note? #22597

kmcallister opened this issue Feb 20, 2015 · 2 comments
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A-diagnostics Area: Messages for errors, warnings, and lints A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

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@kmcallister
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@kmcallister kmcallister added E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) labels Feb 20, 2015
@huonw huonw added the A-diagnostics Area: Messages for errors, warnings, and lints label Feb 20, 2015
@asolove
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asolove commented Apr 25, 2015

I am interested in improving the trace_macros output, but there is a strongly-worded note that trace_macros "is a nasty hack that will certainly be removed." If it's going to be around for a while, though, I might take a crack at this.

The program:

#![feature(trace_macros)]

macro_rules! double {
    ($x:expr) => (2 * $x)
}

fn main() {
    trace_macros!(true);
    println!("{}", double!(21));
}

currently outputs:

println! { "{}" , double ! ( 21 ) }
print! { concat ! ( "{}" , "\n" ) , double ! ( 21 ) }
double! { 21 }
42

What is the desired output? I suspect it includes showing the span of the currently-expanding macro and then showing the expansion back in the original source location?

@brson
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brson commented Jun 27, 2016

Triage: still could be improved, not clear how. Probably not E-easy.

@brson brson removed the E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. label Jun 27, 2016
@estebank estebank mentioned this issue Apr 24, 2017
Merged
frewsxcv added a commit to frewsxcv/rust that referenced this issue May 9, 2017
@frewsxcv
Rollup merge of rust-lang#41520 - estebank:trace-macro, r=nikomatsakis
1940c31 
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.
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A-diagnostics Area: Messages for errors, warnings, and lints A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)
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@asolove @brson @kmcallister @huonw