Point at correct span for arguments in format strings

When a format string has escaped whitespace characters format
arguments were shifted by one per each escaped character. Account
for these escaped characters when synthesizing the spans.

Fix rust-lang#55155.

Author: estebank

src/libfmt_macros/lib.rs

@@ -144,7 +144,7 @@ pub struct Parser<'a> {
     /// `Some(raw count)` when the string is "raw", used to position spans correctly
     style: Option<usize>,
     /// Start and end byte offset of every successfully parsed argument
-    pub arg_places: Vec<(usize, usize)>,
+    pub arg_places: Vec<(SpanIndex, SpanIndex)>,
     /// Characters that need to be shifted
     skips: Vec<usize>,
     /// Span offset of the last opening brace seen, used for error reporting
@@ -154,7 +154,7 @@ pub struct Parser<'a> {
 }
 
 #[derive(Clone, Copy, Debug)]
-pub struct SpanIndex(usize);
+pub struct SpanIndex(pub usize);
 
 impl SpanIndex {
     pub fn unwrap(self) -> usize {
@@ -166,7 +166,6 @@ impl<'a> Iterator for Parser<'a> {
     type Item = Piece<'a>;
 
     fn next(&mut self) -> Option<Piece<'a>> {
-        let raw = self.raw();
         if let Some(&(pos, c)) = self.cur.peek() {
             match c {
                 '{' => {
@@ -180,7 +179,7 @@ impl<'a> Iterator for Parser<'a> {
                     } else {
                         let arg = self.argument();
                         if let Some(arg_pos) = self.must_consume('}').map(|end| {
-                            (pos + raw + 1, end + raw + 2)
+                            (self.to_span_index(pos), self.to_span_index(end + 1))
                         }) {
                             self.arg_places.push(arg_pos);
                         }

src/libsyntax_ext/format.rs

@@ -860,7 +860,9 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt,
     }
 
     let arg_spans = parser.arg_places.iter()
-        .map(|&(start, end)| fmt.span.from_inner_byte_pos(start, end))
+        .map(|&(parse::SpanIndex(start), parse::SpanIndex(end))| {
+            fmt.span.from_inner_byte_pos(start, end)
+        })
         .collect();
 
     let mut cx = Context {

src/test/ui/fmt/format-string-error-2.rs

@@ -67,4 +67,6 @@ raw  { \n
     asdf}
     ", asdf=1);
     //~^^ ERROR invalid format string
+    println!("\t{}");
+    //~^ ERROR 1 positional argument in format string
 }

src/test/ui/fmt/format-string-error-2.stderr

@@ -133,5 +133,11 @@ LL |     asdf}
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
-error: aborting due to 13 previous errors
+error: 1 positional argument in format string, but no arguments were given
+  --> $DIR/format-string-error-2.rs:70:17
+   |
+LL |     println!("/t{}");
+   |                 ^^
+
+error: aborting due to 14 previous errors