From e21d101c45022ab34d5ad10605a16d6ce8116c94 Mon Sep 17 00:00:00 2001
From: Kevin Per <kevin.per@protonmail.com>
Date: Sat, 4 Apr 2020 07:55:07 +0000
Subject: [PATCH] Show open and closed braces of last proper block

---
 src/librustc_parse/lexer/tokentrees.rs        | 48 +++++++++++++++----
 .../issue-70583-block-is-empty-1.stderr       |  6 ++-
 .../macro-mismatched-delim-paren-brace.stderr |  5 ++
 .../mismatched-delim-brace-empty-block.stderr |  6 +++
 4 files changed, 54 insertions(+), 11 deletions(-)

diff --git a/src/librustc_parse/lexer/tokentrees.rs b/src/librustc_parse/lexer/tokentrees.rs
index e7bb8c7cc14..09bbfe10fe5 100644
--- a/src/librustc_parse/lexer/tokentrees.rs
+++ b/src/librustc_parse/lexer/tokentrees.rs
@@ -1,6 +1,6 @@
 use super::{StringReader, UnmatchedBrace};
 
-use rustc_ast::token::{self, Token};
+use rustc_ast::token::{self, Token, DelimToken};
 use rustc_ast::tokenstream::{
     DelimSpan,
     IsJoint::{self, *},
@@ -44,7 +44,7 @@ struct TokenTreesReader<'a> {
     /// Collect empty block spans that might have been auto-inserted by editors.
     last_delim_empty_block_spans: FxHashMap<token::DelimToken, Span>,
     /// Collect the spans of braces (Open, Close). Used only
-    /// for detecting if blocks are empty
+    /// for detecting if blocks are empty and only braces.
     matching_block_spans: Vec<(Span, Span)>,
 }
 
@@ -151,7 +151,13 @@ fn parse_token_tree(&mut self) -> PResult<'a, TreeAndJoint> {
                             }
                         }
 
-                        self.matching_block_spans.push((open_brace_span, close_brace_span));
+                        match (open_brace, delim) {
+                            //only add braces
+                            (DelimToken::Brace, DelimToken::Brace) => {
+                                self.matching_block_spans.push((open_brace_span, close_brace_span));
+                            }
+                            _ => {}
+                        }
 
                         if self.open_braces.is_empty() {
                             // Clear up these spans to avoid suggesting them as we've found
@@ -232,18 +238,42 @@ fn parse_token_tree(&mut self) -> PResult<'a, TreeAndJoint> {
                 let mut err =
                     self.string_reader.sess.span_diagnostic.struct_span_err(self.token.span, &msg);
 
-                if let Some(span) = self.last_delim_empty_block_spans.remove(&delim) {
                     // Braces are added at the end, so the last element is the biggest block
                     if let Some(parent) = self.matching_block_spans.last() {
-                        // Check if the (empty block) is in the last properly closed block
-                        if (parent.0.to(parent.1)).contains(span) {
+
+                        if let Some(span) = self.last_delim_empty_block_spans.remove(&delim) {
+                            // Check if the (empty block) is in the last properly closed block
+                            if (parent.0.to(parent.1)).contains(span) {
+                                err.span_label(
+                                    span,
+                                    "this block is empty, you might have not meant to close it",
+                                );
+                            }
+                            else {
+                                err.span_label(
+                                    parent.0,
+                                    "this opening brace...",
+                                );
+
+                                err.span_label(
+                                    parent.1,
+                                    "...matches this closing brace",
+                                );
+                            }
+                        }
+                        else {
                             err.span_label(
-                                span,
-                                "this block is empty, you might have not meant to close it",
+                                parent.0,
+                                "this opening brace...",
+                            );
+
+                            err.span_label(
+                                parent.1,
+                                "...matches this closing brace",
                             );
                         }
-                    }
                 }
+
                 err.span_label(self.token.span, "unexpected closing delimiter");
                 Err(err)
             }
diff --git a/src/test/ui/parser/issue-70583-block-is-empty-1.stderr b/src/test/ui/parser/issue-70583-block-is-empty-1.stderr
index f4bbe9e86e9..39bf113ef83 100644
--- a/src/test/ui/parser/issue-70583-block-is-empty-1.stderr
+++ b/src/test/ui/parser/issue-70583-block-is-empty-1.stderr
@@ -1,9 +1,11 @@
 error: unexpected closing delimiter: `}`
   --> $DIR/issue-70583-block-is-empty-1.rs:20:1
    |
-LL |             ErrorHandled::Reported => {}
-   |                                       -- this block is empty, you might have not meant to close it
+LL | fn struct_generic(x: Vec<i32>) {
+   |                                - this opening brace...
 ...
+LL |     }
+   |     - ...matches this closing brace
 LL | }
    | ^ unexpected closing delimiter
 
diff --git a/src/test/ui/parser/macro-mismatched-delim-paren-brace.stderr b/src/test/ui/parser/macro-mismatched-delim-paren-brace.stderr
index 042142ac350..424c7a60c19 100644
--- a/src/test/ui/parser/macro-mismatched-delim-paren-brace.stderr
+++ b/src/test/ui/parser/macro-mismatched-delim-paren-brace.stderr
@@ -1,6 +1,11 @@
 error: unexpected closing delimiter: `}`
   --> $DIR/macro-mismatched-delim-paren-brace.rs:5:1
    |
+LL | fn main() {
+   |           - this opening brace...
+...
+LL |     }
+   |     - ...matches this closing brace
 LL | }
    | ^ unexpected closing delimiter
 
diff --git a/src/test/ui/parser/mismatched-delim-brace-empty-block.stderr b/src/test/ui/parser/mismatched-delim-brace-empty-block.stderr
index f1be5dc5ba7..c871e549c9e 100644
--- a/src/test/ui/parser/mismatched-delim-brace-empty-block.stderr
+++ b/src/test/ui/parser/mismatched-delim-brace-empty-block.stderr
@@ -1,6 +1,12 @@
 error: unexpected closing delimiter: `}`
   --> $DIR/mismatched-delim-brace-empty-block.rs:5:1
    |
+LL | fn main() {
+   |           - this opening brace...
+LL | 
+LL | }
+   | - ...matches this closing brace
+LL |     let _ = ();
 LL | }
    | ^ unexpected closing delimiter