From 6c45ebe8faf6e0e3b12a855429b6b732c04179d0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omeragacan@gmail.com>
Date: Sun, 21 Mar 2021 17:29:21 +0300
Subject: [PATCH] format macro argument parsing fix

When the character next to `{}` is "shifted" (when mapping a byte index
in the format string to span) we should avoid shifting the span end
index, so first map the index of `}` to span, then bump the span,
instead of first mapping the next byte index to a span (which causes
bumping the end span too much).

Regression test added.

Fixes #83344
---
 compiler/rustc_parse_format/src/lib.rs | 10 ++++++----
 src/test/ui/macros/issue-83344.rs      |  6 ++++++
 src/test/ui/macros/issue-83344.stderr  |  8 ++++++++
 3 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/macros/issue-83344.rs
 create mode 100644 src/test/ui/macros/issue-83344.stderr

diff --git a/compiler/rustc_parse_format/src/lib.rs b/compiler/rustc_parse_format/src/lib.rs
index 92d974690b514..d49ddbd64c5eb 100644
--- a/compiler/rustc_parse_format/src/lib.rs
+++ b/compiler/rustc_parse_format/src/lib.rs
@@ -213,11 +213,13 @@ impl<'a> Iterator for Parser<'a> {
                         Some(String(self.string(pos + 1)))
                     } else {
                         let arg = self.argument();
-                        if let Some(end) = self.must_consume('}') {
-                            let start = self.to_span_index(pos);
-                            let end = self.to_span_index(end + 1);
+                        if let Some(rbrace_byte_idx) = self.must_consume('}') {
+                            let lbrace_inner_offset = self.to_span_index(pos);
+                            let rbrace_inner_offset = self.to_span_index(rbrace_byte_idx);
                             if self.is_literal {
-                                self.arg_places.push(start.to(end));
+                                self.arg_places.push(
+                                    lbrace_inner_offset.to(InnerOffset(rbrace_inner_offset.0 + 1)),
+                                );
                             }
                         }
                         Some(NextArgument(arg))
diff --git a/src/test/ui/macros/issue-83344.rs b/src/test/ui/macros/issue-83344.rs
new file mode 100644
index 0000000000000..8670425ca653b
--- /dev/null
+++ b/src/test/ui/macros/issue-83344.rs
@@ -0,0 +1,6 @@
+// chekc-fail
+
+fn main() {
+    println!("{}\
+"); //~^ ERROR: 1 positional argument in format string, but no arguments were given
+}
diff --git a/src/test/ui/macros/issue-83344.stderr b/src/test/ui/macros/issue-83344.stderr
new file mode 100644
index 0000000000000..1ef70f87a1fb4
--- /dev/null
+++ b/src/test/ui/macros/issue-83344.stderr
@@ -0,0 +1,8 @@
+error: 1 positional argument in format string, but no arguments were given
+  --> $DIR/issue-83344.rs:4:15
+   |
+LL |     println!("{}\
+   |               ^^
+
+error: aborting due to previous error
+