Auto merge of #42904 - estebank:number-suggestions, r=nikomatsakis

Make suggestion include the line number

When there're more than one suggestions in the same diagnostic, they are
displayed in their own block, instead of inline. In order to reduce
confusion, those blocks now display the line number.

New output:

```
error[E0308]: mismatched types
  --> ../../src/test/ui/block-result/unexpected-return-on-unit.rs:19:5
   |
19 |     foo()
   |     ^^^^^ expected (), found usize
   |
   = note: expected type `()`
              found type `usize`
help: did you mean to add a semicolon here?
   |
19 |     foo();
   |          ^
help: possibly return type missing here?
   |
18 | fn bar() -> usize {
   |          ^^^^^^^^

error: aborting due to previous error(s)
```

Fix #39152.

src/librustc_errors/emitter.rs

@@ -1060,44 +1060,72 @@ impl EmitterWriter {
                                -> io::Result<()> {
         use std::borrow::Borrow;
 
-        let primary_span = suggestion.substitution_spans().next().unwrap();
+        let primary_sub = &suggestion.substitution_parts[0];
         if let Some(ref cm) = self.cm {
             let mut buffer = StyledBuffer::new();
 
-            let lines = cm.span_to_lines(primary_span).unwrap();
+            let lines = cm.span_to_lines(primary_sub.span).unwrap();
 
             assert!(!lines.lines.is_empty());
 
             buffer.append(0, &level.to_string(), Style::Level(level.clone()));
             buffer.append(0, ": ", Style::HeaderMsg);
             self.msg_to_buffer(&mut buffer,
-                            &[(suggestion.msg.to_owned(), Style::NoStyle)],
+                               &[(suggestion.msg.to_owned(), Style::NoStyle)],
-                            max_line_num_len,
+                               max_line_num_len,
-                            "suggestion",
+                               "suggestion",
-                            Some(Style::HeaderMsg));
+                               Some(Style::HeaderMsg));
 
             let suggestions = suggestion.splice_lines(cm.borrow());
-            let mut row_num = 1;
+            let span_start_pos = cm.lookup_char_pos(primary_sub.span.lo);
-            for complete in suggestions.iter().take(MAX_SUGGESTIONS) {
+            let line_start = span_start_pos.line;
-
+            draw_col_separator_no_space(&mut buffer, 1, max_line_num_len + 1);
-                // print the suggestion without any line numbers, but leave
+            let mut row_num = 2;
-                // space for them. This helps with lining up with previous
+            for (&(ref complete, show_underline), ref sub) in suggestions
-                // snippets from the actual error being reported.
+                    .iter().zip(primary_sub.substitutions.iter()).take(MAX_SUGGESTIONS)
+            {
+                let mut line_pos = 0;
+                // Only show underline if there's a single suggestion and it is a single line
                 let mut lines = complete.lines();
                 for line in lines.by_ref().take(MAX_HIGHLIGHT_LINES) {
+                    // Print the span column to avoid confusion
+                    buffer.puts(row_num,
+                                0,
+                                &((line_start + line_pos).to_string()),
+                                Style::LineNumber);
+                    // print the suggestion
                     draw_col_separator(&mut buffer, row_num, max_line_num_len + 1);
                     buffer.append(row_num, line, Style::NoStyle);
+                    line_pos += 1;
                     row_num += 1;
+                    // Only show an underline in the suggestions if the suggestion is not the
+                    // entirety of the code being shown and the displayed code is not multiline.
+                    if show_underline {
+                        draw_col_separator(&mut buffer, row_num, max_line_num_len + 1);
+                        let sub_len = sub.trim_right().len();
+                        let underline_start = span_start_pos.col.0;
+                        let underline_end = span_start_pos.col.0 + sub_len;
+                        for p in underline_start..underline_end {
+                            buffer.putc(row_num,
+                                        max_line_num_len + 3 + p,
+                                        '^',
+                                        Style::UnderlinePrimary);
+                        }
+                        row_num += 1;
+                    }
                 }
 
                 // if we elided some lines, add an ellipsis
                 if let Some(_) = lines.next() {
-                    buffer.append(row_num, "...", Style::NoStyle);
+                    buffer.puts(row_num, max_line_num_len - 1, "...", Style::LineNumber);
+                } else if !show_underline {
+                    draw_col_separator_no_space(&mut buffer, row_num, max_line_num_len + 1);
+                    row_num += 1;
                 }
             }
             if suggestions.len() > MAX_SUGGESTIONS {
                 let msg = format!("and {} other candidates", suggestions.len() - MAX_SUGGESTIONS);
-                buffer.append(row_num, &msg, Style::NoStyle);
+                buffer.puts(row_num, 0, &msg, Style::NoStyle);
             }
             emit_to_destination(&buffer.render(), level, &mut self.dst)?;
         }

src/librustc_errors/lib.rs

@@ -114,8 +114,8 @@ impl CodeSuggestion {
         self.substitution_parts.iter().map(|sub| sub.span)
     }
 
-    /// Returns the assembled code suggestions.
+    /// Returns the assembled code suggestions and wether they should be shown with an underline.
-    pub fn splice_lines(&self, cm: &CodeMapper) -> Vec<String> {
+    pub fn splice_lines(&self, cm: &CodeMapper) -> Vec<(String, bool)> {
         use syntax_pos::{CharPos, Loc, Pos};
 
         fn push_trailing(buf: &mut String,
@@ -138,7 +138,7 @@ impl CodeSuggestion {
         }
 
         if self.substitution_parts.is_empty() {
-            return vec![String::new()];
+            return vec![(String::new(), false)];
         }
 
         let mut primary_spans: Vec<_> = self.substitution_parts
@@ -175,14 +175,25 @@ impl CodeSuggestion {
         prev_hi.col = CharPos::from_usize(0);
 
         let mut prev_line = fm.get_line(lines.lines[0].line_index);
-        let mut bufs = vec![String::new(); self.substitutions()];
+        let mut bufs = vec![(String::new(), false); self.substitutions()];
 
         for (sp, substitutes) in primary_spans {
             let cur_lo = cm.lookup_char_pos(sp.lo);
-            for (buf, substitute) in bufs.iter_mut().zip(substitutes) {
+            for (&mut (ref mut buf, ref mut underline), substitute) in bufs.iter_mut()
+                                                                           .zip(substitutes) {
                 if prev_hi.line == cur_lo.line {
                     push_trailing(buf, prev_line.as_ref(), &prev_hi, Some(&cur_lo));
+
+                    // Only show an underline in the suggestions if the suggestion is not the
+                    // entirety of the code being shown and the displayed code is not multiline.
+                    if prev_line.as_ref().unwrap().trim().len() > 0
+                        && !substitute.ends_with('\n')
+                        && substitute.lines().count() == 1
+                    {
+                        *underline = true;
+                    }
                 } else {
+                    *underline = false;
                     push_trailing(buf, prev_line.as_ref(), &prev_hi, None);
                     // push lines between the previous and current span (if any)
                     for idx in prev_hi.line..(cur_lo.line - 1) {
@@ -200,7 +211,7 @@ impl CodeSuggestion {
             prev_hi = cm.lookup_char_pos(sp.hi);
             prev_line = fm.get_line(prev_hi.line - 1);
         }
-        for buf in &mut bufs {
+        for &mut (ref mut buf, _) in &mut bufs {
             // if the replacement already ends with a newline, don't print the next line
             if !buf.ends_with('\n') {
                 push_trailing(buf, prev_line.as_ref(), &prev_hi, None);

src/libsyntax/json.rs

@@ -359,7 +359,7 @@ impl DiagnosticCode {
 
 impl JsonEmitter {
     fn render(&self, suggestion: &CodeSuggestion) -> Vec<String> {
-        suggestion.splice_lines(&*self.cm)
+        suggestion.splice_lines(&*self.cm).iter().map(|line| line.0.to_owned()).collect()
     }
 }
 

src/libsyntax/parse/parser.rs

@@ -2920,10 +2920,6 @@ impl<'a> Parser<'a> {
                         err.cancel();
                         let codemap = self.sess.codemap();
                         let suggestion_span = lhs_span.to(self.prev_span);
-                        let suggestion = match codemap.span_to_snippet(suggestion_span) {
-                            Ok(lstring) => format!("({})", lstring),
-                            _ => format!("(<expression> as <type>)")
-                        };
                         let warn_message = match codemap.span_to_snippet(self.prev_span) {
                             Ok(lstring) => format!("`{}`", lstring),
                             _ => "a type".to_string(),
@@ -2934,6 +2930,10 @@ impl<'a> Parser<'a> {
                         let mut err = self.sess.span_diagnostic.struct_span_err(sp, &msg);
                         err.span_label(sp, "interpreted as generic argument");
                         err.span_label(self.span, "not interpreted as comparison");
+                        let suggestion = match codemap.span_to_snippet(suggestion_span) {
+                            Ok(lstring) => format!("({})", lstring),
+                            _ => format!("(<expression> as <type>)")
+                        };
                         err.span_suggestion(suggestion_span,
                                             "if you want to compare the casted value then write:",
                                             suggestion);

src/test/ui/block-result/unexpected-return-on-unit.stderr

@@ -7,9 +7,13 @@ error[E0308]: mismatched types
    = note: expected type `()`
               found type `usize`
 help: did you mean to add a semicolon here?
-   |     foo();
+   |
+19 |     foo();
+   |          ^
 help: possibly return type missing here?
-   | fn bar() -> usize {
+   |
+18 | fn bar() -> usize {
+   |          ^^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/issue-22644.rs

@@ -14,5 +14,18 @@ fn main() {
 
     println!("{}", a as usize > b);
     println!("{}", a as usize < b);
-    println!("{}", a as usize < 4);
+    println!("{}", a
+                   as
+                   usize
+                   <
+                   4);
+    println!("{}", a
+
+
+                   as
+
+
+                   usize
+                   <
+                   5);
 }

src/test/ui/issue-22644.stderr

@@ -7,18 +7,42 @@ error: `<` is interpreted as a start of generic arguments for `usize`, not a com
    |                               not interpreted as comparison
    |
 help: if you want to compare the casted value then write:
-   |     println!("{}", (a as usize) < b);
+   |
+16 |     println!("{}", (a as usize) < b);
+   |                    ^^^^^^^^^^^^
 
 error: `<` is interpreted as a start of generic arguments for `usize`, not a comparison
-  --> $DIR/issue-22644.rs:17:33
+  --> $DIR/issue-22644.rs:21:20
    |
-17 |     println!("{}", a as usize < 4);
+20 |                    <
-   |                               - ^ interpreted as generic argument
+   |                    - not interpreted as comparison
-   |                               |
+21 |                    4);
-   |                               not interpreted as comparison
+   |                    ^ interpreted as generic argument
    |
 help: if you want to compare the casted value then write:
-   |     println!("{}", (a as usize) < 4);
+   |
+17 |     println!("{}", (a
+18 |                    as
+19 |                    usize)
+   |
 
-error: aborting due to 2 previous errors
+error: `<` is interpreted as a start of generic arguments for `usize`, not a comparison
+  --> $DIR/issue-22644.rs:30:20
+   |
+29 |                    <
+   |                    - not interpreted as comparison
+30 |                    5);
+   |                    ^ interpreted as generic argument
+   |
+help: if you want to compare the casted value then write:
+   |
+22 |     println!("{}", (a
+23 | 
+24 | 
+25 |                    as
+26 | 
+27 | 
+ ...
+
+error: aborting due to 3 previous errors
 

src/test/ui/resolve/enums-are-namespaced-xc.stderr

@@ -5,7 +5,9 @@ error[E0425]: cannot find value `A` in module `namespaced_enums`
    |                               ^ not found in `namespaced_enums`
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use namespaced_enums::Foo::A;
+   |
+12 | use namespaced_enums::Foo::A;
+   |
 
 error[E0425]: cannot find function `B` in module `namespaced_enums`
   --> $DIR/enums-are-namespaced-xc.rs:18:31
@@ -14,7 +16,9 @@ error[E0425]: cannot find function `B` in module `namespaced_enums`
    |                               ^ not found in `namespaced_enums`
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use namespaced_enums::Foo::B;
+   |
+12 | use namespaced_enums::Foo::B;
+   |
 
 error[E0422]: cannot find struct, variant or union type `C` in module `namespaced_enums`
   --> $DIR/enums-are-namespaced-xc.rs:21:31
@@ -23,7 +27,9 @@ error[E0422]: cannot find struct, variant or union type `C` in module `namespace
    |                               ^ not found in `namespaced_enums`
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use namespaced_enums::Foo::C;
+   |
+12 | use namespaced_enums::Foo::C;
+   |
 
 error: aborting due to 3 previous errors
 

src/test/ui/resolve/issue-16058.stderr

@@ -5,9 +5,13 @@ error[E0574]: expected struct, variant or union type, found enum `Result`
    |         ^^^^^^ not a struct, variant or union type
    |
 help: possible better candidates are found in other modules, you can import them into scope
-   | use std::fmt::Result;
+   |
-   | use std::io::Result;
+12 | use std::fmt::Result;
-   | use std::thread::Result;
+   |
+12 | use std::io::Result;
+   |
+12 | use std::thread::Result;
+   |
 
 error: aborting due to previous error
 

src/test/ui/resolve/issue-17518.stderr

@@ -5,7 +5,9 @@ error[E0422]: cannot find struct, variant or union type `E` in this scope
    |     ^ not found in this scope
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use SomeEnum::E;
+   |
+11 | use SomeEnum::E;
+   |
 
 error: aborting due to previous error
 

src/test/ui/resolve/issue-21221-1.stderr

@@ -5,9 +5,13 @@ error[E0405]: cannot find trait `Mul` in this scope
    |      ^^^ not found in this scope
    |
 help: possible candidates are found in other modules, you can import them into scope
-   | use mul1::Mul;
+   |
-   | use mul2::Mul;
+11 | use mul1::Mul;
-   | use std::ops::Mul;
+   |
+11 | use mul2::Mul;
+   |
+11 | use std::ops::Mul;
+   |
 
 error[E0412]: cannot find type `Mul` in this scope
   --> $DIR/issue-21221-1.rs:72:16
@@ -16,10 +20,15 @@ error[E0412]: cannot find type `Mul` in this scope
    |                ^^^ not found in this scope
    |
 help: possible candidates are found in other modules, you can import them into scope
-   | use mul1::Mul;
+   |
-   | use mul2::Mul;
+11 | use mul1::Mul;
-   | use mul3::Mul;
+   |
-   | use mul4::Mul;
+11 | use mul2::Mul;
+   |
+11 | use mul3::Mul;
+   |
+11 | use mul4::Mul;
+   |
 and 2 other candidates
 
 error[E0405]: cannot find trait `ThisTraitReallyDoesntExistInAnyModuleReally` in this scope
@@ -35,7 +44,9 @@ error[E0405]: cannot find trait `Div` in this scope
    |      ^^^ not found in this scope
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use std::ops::Div;
+   |
+11 | use std::ops::Div;
+   |
 
 error: cannot continue compilation due to previous error
 

src/test/ui/resolve/issue-21221-2.stderr

@@ -5,7 +5,9 @@ error[E0405]: cannot find trait `T` in this scope
    |      ^ not found in this scope
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use foo::bar::T;
+   |
+11 | use foo::bar::T;
+   |
 
 error[E0601]: main function not found
 

src/test/ui/resolve/issue-21221-3.stderr

@@ -5,7 +5,9 @@ error[E0405]: cannot find trait `OuterTrait` in this scope
    |      ^^^^^^^^^^ not found in this scope
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use issue_21221_3::outer::OuterTrait;
+   |
+16 | use issue_21221_3::outer::OuterTrait;
+   |
 
 error: cannot continue compilation due to previous error
 

src/test/ui/resolve/issue-21221-4.stderr

@@ -5,7 +5,9 @@ error[E0405]: cannot find trait `T` in this scope
    |      ^ not found in this scope
    |
 help: possible candidate is found in another module, you can import it into scope
-   | use issue_21221_4::T;
+   |
+16 | use issue_21221_4::T;
+   |
 
 error: cannot continue compilation due to previous error
 

src/test/ui/resolve/issue-3907.stderr

@@ -5,7 +5,9 @@ error[E0404]: expected trait, found type alias `Foo`
    |      ^^^ type aliases cannot be used for traits
    |
 help: possible better candidate is found in another module, you can import it into scope
-   | use issue_3907::Foo;
+   |
+12 | use issue_3907::Foo;
+   |
 
 error: cannot continue compilation due to previous error
 

src/test/ui/resolve/privacy-struct-ctor.stderr

@@ -9,7 +9,9 @@ error[E0423]: expected value, found struct `Z`
    |         constructor is not visible here due to private fields
    |
 help: possible better candidate is found in another module, you can import it into scope
-   | use m::n::Z;
+   |
+15 | use m::n::Z;
+   |
 
 error[E0423]: expected value, found struct `S`
   --> $DIR/privacy-struct-ctor.rs:36:5
@@ -21,7 +23,9 @@ error[E0423]: expected value, found struct `S`
    |     constructor is not visible here due to private fields
    |
 help: possible better candidate is found in another module, you can import it into scope
-   | use m::S;
+   |
+13 | use m::S;
+   |
 
 error[E0423]: expected value, found struct `xcrate::S`
   --> $DIR/privacy-struct-ctor.rs:42:5
@@ -33,7 +37,9 @@ error[E0423]: expected value, found struct `xcrate::S`
    |     constructor is not visible here due to private fields
    |
 help: possible better candidate is found in another module, you can import it into scope
-   | use m::S;
+   |
+13 | use m::S;
+   |
 
 error[E0603]: tuple struct `Z` is private
   --> $DIR/privacy-struct-ctor.rs:25:9

src/test/ui/span/issue-35987.stderr

@@ -5,7 +5,9 @@ error[E0404]: expected trait, found type parameter `Add`
    |                     ^^^ not a trait
    |
 help: possible better candidate is found in another module, you can import it into scope
-   | use std::ops::Add;
+   |
+11 | use std::ops::Add;
+   |
 
 error[E0601]: main function not found
 

src/test/ui/span/issue-39018.stderr

@@ -5,7 +5,9 @@ error[E0369]: binary operation `+` cannot be applied to type `&'static str`
    |             ^^^^^^^^^^^^^^^^^^^ `+` can't be used to concatenate two `&str` strings
    |
 help: `to_owned()` can be used to create an owned `String` from a string reference. String concatenation appends the string on the right to the string on the left and may require reallocation. This requires ownership of the string on the left.
-   |     let x = "Hello ".to_owned() + "World!";
+   |
+12 |     let x = "Hello ".to_owned() + "World!";
+   |             ^^^^^^^^^^^^^^^^^^^
 
 error[E0369]: binary operation `+` cannot be applied to type `World`
   --> $DIR/issue-39018.rs:17:13