Rollup merge of #113774 - compiler-errors:fill-expr-bracket, r=eholk

Improve error message when closing bracket interpreted as formatting fill character

Fixes #112732 by explaining why it's erroring in the way it is.

8 files changed, 97 insertions, 75 deletions

diff --git a/compiler/rustc_parse_format/src/lib.rs b/compiler/rustc_parse_format/src/lib.rs
index 7de84db211e..88452ccdf05 100644
--- a/compiler/rustc_parse_format/src/lib.rs
+++ b/compiler/rustc_parse_format/src/lib.rs
@@ -109,6 +109,8 @@ pub struct Argument<'a> {
 pub struct FormatSpec<'a> {
     /// Optionally specified character to fill alignment with.
     pub fill: Option<char>,
+    /// Span of the optionally specified fill character.
+    pub fill_span: Option<InnerSpan>,
     /// Optionally specified alignment.
     pub align: Alignment,
     /// The `+` or `-` flag.
@@ -264,7 +266,7 @@ impl<'a> Iterator for Parser<'a> {
                         Some(String(self.string(pos + 1)))
                     } else {
                         let arg = self.argument(lbrace_end);
-                        if let Some(rbrace_pos) = self.must_consume('}') {
+                        if let Some(rbrace_pos) = self.consume_closing_brace(&arg) {
                             if self.is_source_literal {
                                 let lbrace_byte_pos = self.to_span_index(pos);
                                 let rbrace_byte_pos = self.to_span_index(rbrace_pos);
@@ -450,69 +452,51 @@ impl<'a> Parser<'a> {
 
     /// Forces consumption of the specified character. If the character is not
     /// found, an error is emitted.
-    fn must_consume(&mut self, c: char) -> Option<usize> {
+    fn consume_closing_brace(&mut self, arg: &Argument<'_>) -> Option<usize> {
         self.ws();
 
-        if let Some(&(pos, maybe)) = self.cur.peek() {
-            if c == maybe {
+        let pos;
+        let description;
+
+        if let Some(&(peek_pos, maybe)) = self.cur.peek() {
+            if maybe == '}' {
                 self.cur.next();
-                Some(pos)
-            } else {
-                let pos = self.to_span_index(pos);
-                let description = format!("expected `'}}'`, found `{maybe:?}`");
-                let label = "expected `}`".to_owned();
-                let (note, secondary_label) = if c == '}' {
-                    (
-                        Some(
-                            "if you intended to print `{`, you can escape it using `{{`".to_owned(),
-                        ),
-                        self.last_opening_brace
-                            .map(|sp| ("because of this opening brace".to_owned(), sp)),
-                    )
-                } else {
-                    (None, None)
-                };
-                self.errors.push(ParseError {
-                    description,
-                    note,
-                    label,
-                    span: pos.to(pos),
-                    secondary_label,
-                    should_be_replaced_with_positional_argument: false,
-                });
-                None
+                return Some(peek_pos);
             }
+
+            pos = peek_pos;
+            description = format!("expected `'}}'`, found `{maybe:?}`");
         } else {
-            let description = format!("expected `{c:?}` but string was terminated");
+            description = "expected `'}'` but string was terminated".to_owned();
             // point at closing `"`
-            let pos = self.input.len() - if self.append_newline { 1 } else { 0 };
-            let pos = self.to_span_index(pos);
-            if c == '}' {
-                let label = format!("expected `{c:?}`");
-                let (note, secondary_label) = if c == '}' {
-                    (
-                        Some(
-                            "if you intended to print `{`, you can escape it using `{{`".to_owned(),
-                        ),
-                        self.last_opening_brace
-                            .map(|sp| ("because of this opening brace".to_owned(), sp)),
-                    )
-                } else {
-                    (None, None)
-                };
-                self.errors.push(ParseError {
-                    description,
-                    note,
-                    label,
-                    span: pos.to(pos),
-                    secondary_label,
-                    should_be_replaced_with_positional_argument: false,
-                });
-            } else {
-                self.err(description, format!("expected `{c:?}`"), pos.to(pos));
-            }
-            None
+            pos = self.input.len() - if self.append_newline { 1 } else { 0 };
         }
+
+        let pos = self.to_span_index(pos);
+
+        let label = "expected `'}'`".to_owned();
+        let (note, secondary_label) = if arg.format.fill == Some('}') {
+            (
+                Some("the character `'}'` is interpreted as a fill character because of the `:` that precedes it".to_owned()),
+                arg.format.fill_span.map(|sp| ("this is not interpreted as a formatting closing brace".to_owned(), sp)),
+            )
+        } else {
+            (
+                Some("if you intended to print `{`, you can escape it using `{{`".to_owned()),
+                self.last_opening_brace.map(|sp| ("because of this opening brace".to_owned(), sp)),
+            )
+        };
+
+        self.errors.push(ParseError {
+            description,
+            note,
+            label,
+            span: pos.to(pos),
+            secondary_label,
+            should_be_replaced_with_positional_argument: false,
+        });
+
+        None
     }
 
     /// Consumes all whitespace characters until the first non-whitespace character
@@ -608,6 +592,7 @@ impl<'a> Parser<'a> {
     fn format(&mut self) -> FormatSpec<'a> {
         let mut spec = FormatSpec {
             fill: None,
+            fill_span: None,
             align: AlignUnknown,
             sign: None,
             alternate: false,
@@ -625,9 +610,10 @@ impl<'a> Parser<'a> {
         }
 
         // fill character
-        if let Some(&(_, c)) = self.cur.peek() {
+        if let Some(&(idx, c)) = self.cur.peek() {
             if let Some((_, '>' | '<' | '^')) = self.cur.clone().nth(1) {
                 spec.fill = Some(c);
+                spec.fill_span = Some(self.span(idx, idx + 1));
                 self.cur.next();
             }
         }
@@ -722,6 +708,7 @@ impl<'a> Parser<'a> {
     fn inline_asm(&mut self) -> FormatSpec<'a> {
         let mut spec = FormatSpec {
             fill: None,
+            fill_span: None,
             align: AlignUnknown,
             sign: None,
             alternate: false,
diff --git a/compiler/rustc_parse_format/src/tests.rs b/compiler/rustc_parse_format/src/tests.rs
index 45314e2fb55..0c594f9104c 100644
--- a/compiler/rustc_parse_format/src/tests.rs
+++ b/compiler/rustc_parse_format/src/tests.rs
@@ -9,6 +9,7 @@ fn same(fmt: &'static str, p: &[Piece<'static>]) {
 fn fmtdflt() -> FormatSpec<'static> {
     return FormatSpec {
         fill: None,
+        fill_span: None,
         align: AlignUnknown,
         sign: None,
         alternate: false,
@@ -128,6 +129,7 @@ fn format_type() {
             position_span: InnerSpan { start: 2, end: 3 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -152,6 +154,7 @@ fn format_align_fill() {
             position_span: InnerSpan { start: 2, end: 3 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignRight,
                 sign: None,
                 alternate: false,
@@ -173,6 +176,7 @@ fn format_align_fill() {
             position_span: InnerSpan { start: 2, end: 3 },
             format: FormatSpec {
                 fill: Some('0'),
+                fill_span: Some(InnerSpan::new(4, 5)),
                 align: AlignLeft,
                 sign: None,
                 alternate: false,
@@ -194,6 +198,7 @@ fn format_align_fill() {
             position_span: InnerSpan { start: 2, end: 3 },
             format: FormatSpec {
                 fill: Some('*'),
+                fill_span: Some(InnerSpan::new(4, 5)),
                 align: AlignLeft,
                 sign: None,
                 alternate: false,
@@ -218,6 +223,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -239,6 +245,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -260,6 +267,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 3 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -281,6 +289,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -302,6 +311,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -323,6 +333,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -344,6 +355,7 @@ fn format_counts() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: None,
                 alternate: false,
@@ -368,6 +380,7 @@ fn format_flags() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: Some(Sign::Minus),
                 alternate: false,
@@ -389,6 +402,7 @@ fn format_flags() {
             position_span: InnerSpan { start: 2, end: 2 },
             format: FormatSpec {
                 fill: None,
+                fill_span: None,
                 align: AlignUnknown,
                 sign: Some(Sign::Plus),
                 alternate: true,
@@ -415,6 +429,7 @@ fn format_mixture() {
                 position_span: InnerSpan { start: 7, end: 8 },
                 format: FormatSpec {
                     fill: None,
+                    fill_span: None,
                     align: AlignUnknown,
                     sign: None,
                     alternate: false,
diff --git a/tests/ui/fmt/closing-brace-as-fill.rs b/tests/ui/fmt/closing-brace-as-fill.rs
new file mode 100644
index 00000000000..6ad257f943e
--- /dev/null
+++ b/tests/ui/fmt/closing-brace-as-fill.rs
@@ -0,0 +1,8 @@
+// issue: 112732
+
+// `}` is typoed since it is interpreted as a fill character rather than a closing bracket
+
+fn main() {
+    println!("Hello, world! {0:}<3", 2);
+    //~^ ERROR invalid format string: expected `'}'` but string was terminated
+}
diff --git a/tests/ui/fmt/closing-brace-as-fill.stderr b/tests/ui/fmt/closing-brace-as-fill.stderr
new file mode 100644
index 00000000000..aa1e5aff652
--- /dev/null
+++ b/tests/ui/fmt/closing-brace-as-fill.stderr
@@ -0,0 +1,12 @@
+error: invalid format string: expected `'}'` but string was terminated
+  --> $DIR/closing-brace-as-fill.rs:6:35
+   |
+LL |     println!("Hello, world! {0:}<3", 2);
+   |                                -  ^ expected `'}'` in format string
+   |                                |
+   |                                this is not interpreted as a formatting closing brace
+   |
+   = note: the character `'}'` is interpreted as a fill character because of the `:` that precedes it
+
+error: aborting due to previous error
+
diff --git a/tests/ui/fmt/format-string-error-2.stderr b/tests/ui/fmt/format-string-error-2.stderr
index 76cdfbb93bf..dfd24bf60ad 100644
--- a/tests/ui/fmt/format-string-error-2.stderr
+++ b/tests/ui/fmt/format-string-error-2.stderr
@@ -10,7 +10,7 @@ error: invalid format string: expected `'}'`, found `'a'`
 LL |     format!("{
    |              - because of this opening brace
 LL |     a");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -21,7 +21,7 @@ LL |     format!("{ \
    |              - because of this opening brace
 LL |                \
 LL |     b");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -29,7 +29,7 @@ error: invalid format string: expected `'}'`, found `'\'`
   --> $DIR/format-string-error-2.rs:11:18
    |
 LL |     format!(r#"{ \
-   |                - ^ expected `}` in format string
+   |                - ^ expected `'}'` in format string
    |                |
    |                because of this opening brace
    |
@@ -39,7 +39,7 @@ error: invalid format string: expected `'}'`, found `'\'`
   --> $DIR/format-string-error-2.rs:15:18
    |
 LL |     format!(r#"{ \n
-   |                - ^ expected `}` in format string
+   |                - ^ expected `'}'` in format string
    |                |
    |                because of this opening brace
    |
@@ -52,7 +52,7 @@ LL |     format!("{ \n
    |              - because of this opening brace
 LL | \n
 LL |     e");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -62,7 +62,7 @@ error: invalid format string: expected `'}'`, found `'a'`
 LL |     {
    |     - because of this opening brace
 LL |     a");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -72,7 +72,7 @@ error: invalid format string: expected `'}'`, found `'a'`
 LL |     {
    |     - because of this opening brace
 LL |     a
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -83,7 +83,7 @@ LL |     { \
    |     - because of this opening brace
 LL |         \
 LL |     b");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -94,7 +94,7 @@ LL |     { \
    |     - because of this opening brace
 LL |         \
 LL |     b \
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -102,7 +102,7 @@ error: invalid format string: expected `'}'`, found `'\'`
   --> $DIR/format-string-error-2.rs:45:8
    |
 LL | raw  { \
-   |      - ^ expected `}` in format string
+   |      - ^ expected `'}'` in format string
    |      |
    |      because of this opening brace
    |
@@ -112,7 +112,7 @@ error: invalid format string: expected `'}'`, found `'\'`
   --> $DIR/format-string-error-2.rs:50:8
    |
 LL | raw  { \n
-   |      - ^ expected `}` in format string
+   |      - ^ expected `'}'` in format string
    |      |
    |      because of this opening brace
    |
@@ -125,7 +125,7 @@ LL |   { \n
    |   - because of this opening brace
 LL | \n
 LL |     e");
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
@@ -135,7 +135,7 @@ error: invalid format string: expected `'}'`, found `'a'`
 LL |     {
    |     - because of this opening brace
 LL |     asdf}
-   |     ^ expected `}` in format string
+   |     ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`
 
diff --git a/tests/ui/fmt/format-string-error.stderr b/tests/ui/fmt/format-string-error.stderr
index 8a32c225485..37a181e6fcb 100644
--- a/tests/ui/fmt/format-string-error.stderr
+++ b/tests/ui/fmt/format-string-error.stderr
@@ -62,7 +62,7 @@ error: invalid format string: expected `'}'`, found `'\'`
   --> $DIR/format-string-error.rs:19:23
    |
 LL |     let _ = format!("{\}");
-   |                      -^ expected `}` in format string
+   |                      -^ expected `'}'` in format string
    |                      |
    |                      because of this opening brace
    |
diff --git a/tests/ui/fmt/format-string-wrong-order.stderr b/tests/ui/fmt/format-string-wrong-order.stderr
index 461af354a4e..0a2e04026d9 100644
--- a/tests/ui/fmt/format-string-wrong-order.stderr
+++ b/tests/ui/fmt/format-string-wrong-order.stderr
@@ -26,7 +26,7 @@ error: invalid format string: expected `'}'`, found `'?'`
   --> $DIR/format-string-wrong-order.rs:9:15
    |
 LL |     format!("{??}", bar);
-   |              -^ expected `}` in format string
+   |              -^ expected `'}'` in format string
    |              |
    |              because of this opening brace
    |
@@ -36,7 +36,7 @@ error: invalid format string: expected `'}'`, found `'?'`
   --> $DIR/format-string-wrong-order.rs:11:15
    |
 LL |     format!("{?;bar}");
-   |              -^ expected `}` in format string
+   |              -^ expected `'}'` in format string
    |              |
    |              because of this opening brace
    |
diff --git a/tests/ui/fmt/ifmt-bad-arg.stderr b/tests/ui/fmt/ifmt-bad-arg.stderr
index ed008c454a3..09ce3dca411 100644
--- a/tests/ui/fmt/ifmt-bad-arg.stderr
+++ b/tests/ui/fmt/ifmt-bad-arg.stderr
@@ -178,7 +178,7 @@ error: invalid format string: expected `'}'`, found `'t'`
 LL | ninth number: {
    |               - because of this opening brace
 LL | tenth number: {}",
-   | ^ expected `}` in format string
+   | ^ expected `'}'` in format string
    |
    = note: if you intended to print `{`, you can escape it using `{{`