Resolve issue : Somewhat confusing error with extended_key_value_attributes

compiler/rustc_parse/src/parser/expr.rs

@@ -1493,6 +1493,20 @@ impl<'a> Parser<'a> {
 
     pub(super) fn parse_lit(&mut self) -> PResult<'a, Lit> {
         self.parse_opt_lit().ok_or_else(|| {
+            if let token::Interpolated(inner) = &self.token.kind {
+                let expr = match inner.as_ref() {
+                    token::NtExpr(expr) => Some(expr),
+                    token::NtLiteral(expr) => Some(expr),
+                    _ => None,
+                };
+                if let Some(expr) = expr {
+                    if matches!(expr.kind, ExprKind::Err) {
+                        self.diagnostic()
+                            .delay_span_bug(self.token.span, &"invalid interpolated expression");
+                        return self.diagnostic().struct_dummy();
+                    }
+                }
+            }
             let msg = format!("unexpected token: {}", super::token_descr(&self.token));
             self.struct_span_err(self.token.span, &msg)
         })

src/test/ui/attributes/extented-attribute-macro-error.rs

@@ -0,0 +1,8 @@
+// normalize-stderr-test: "couldn't read.*" -> "couldn't read the file"
+
+#![feature(extended_key_value_attributes)]
+#![doc = include_str!("../not_existing_file.md")]
+struct Documented {}
+//~^^ ERROR couldn't read
+
+fn main() {}

src/test/ui/attributes/extented-attribute-macro-error.stderr

@@ -0,0 +1,10 @@
+error: couldn't read the file
+  --> $DIR/extented-attribute-macro-error.rs:4:10
+   |
+LL | #![doc = include_str!("../not_existing_file.md")]
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the macro `include_str` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error
+