Check if format argument is identifier to avoid error err-emit

compiler/rustc_parse_format/src/lib.rs

@@ -100,6 +100,30 @@ pub struct Argument<'a> {
     pub format: FormatSpec<'a>,
 }
 
+impl<'a> Argument<'a> {
+    pub fn is_identifier(&self) -> bool {
+        matches!(self.position, Position::ArgumentNamed(_))
+            && matches!(
+                self.format,
+                FormatSpec {
+                    fill: None,
+                    fill_span: None,
+                    align: AlignUnknown,
+                    sign: None,
+                    alternate: false,
+                    zero_pad: false,
+                    debug_hex: None,
+                    precision: CountImplied,
+                    precision_span: None,
+                    width: CountImplied,
+                    width_span: None,
+                    ty: "",
+                    ty_span: None,
+                },
+            )
+    }
+}
+
 /// Specification for the formatting of an argument in the format string.
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub struct FormatSpec<'a> {
@@ -894,6 +918,11 @@ impl<'a> Parser<'a> {
     }
 
     fn suggest_positional_arg_instead_of_captured_arg(&mut self, arg: Argument<'a>) {
+        // If the argument is not an identifier, it is not a field access.
+        if !arg.is_identifier() {
+            return;
+        }
+
         if let Some(end) = self.consume_pos('.') {
             let byte_pos = self.to_span_index(end);
             let start = InnerOffset(byte_pos.0 + 1);

tests/ui/parser/issues/invalid-parse-format-issue-139104.rs

@@ -0,0 +1,13 @@
+fn main() {
+    println!("{foo:_1.4}", foo = 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+    println!("{0:_1.4}", 1.11); //~ ERROR invalid format string: expected `}`, found `.`
+    println!("{:_1.4}", 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+
+    println!("{foo:_1.4", foo = 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+    println!("{0:_1.4", 1.11); //~ ERROR invalid format string: expected `}`, found `.`
+    println!("{:_1.4", 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+
+    println!("{  0", 1.11); //~ ERROR invalid format string: expected `}`, found `0`
+    println!("{foo:1.4_1.4}", foo = 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+    println!("{0:1.4_1.4}", 3.14); //~ ERROR invalid format string: expected `}`, found `.`
+}

tests/ui/parser/issues/invalid-parse-format-issue-139104.stderr

@@ -0,0 +1,92 @@
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:2:22
+   |
+LL |     println!("{foo:_1.4}", foo = 3.14);
+   |               -      ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:3:20
+   |
+LL |     println!("{0:_1.4}", 1.11);
+   |               -    ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:4:19
+   |
+LL |     println!("{:_1.4}", 3.14);
+   |               -   ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:6:22
+   |
+LL |     println!("{foo:_1.4", foo = 3.14);
+   |               -      ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:7:20
+   |
+LL |     println!("{0:_1.4", 1.11);
+   |               -    ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:8:19
+   |
+LL |     println!("{:_1.4", 3.14);
+   |               -   ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `0`
+  --> $DIR/invalid-parse-format-issue-139104.rs:10:18
+   |
+LL |     println!("{  0", 1.11);
+   |               -  ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:11:25
+   |
+LL |     println!("{foo:1.4_1.4}", foo = 3.14);
+   |               -         ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: invalid format string: expected `}`, found `.`
+  --> $DIR/invalid-parse-format-issue-139104.rs:12:23
+   |
+LL |     println!("{0:1.4_1.4}", 3.14);
+   |               -       ^ expected `}` in format string
+   |               |
+   |               because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error: aborting due to 9 previous errors
+