Fix detection of main function if there are expressions around it

src/librustdoc/doctest/make.rs

@@ -407,15 +407,19 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
                     push_to_s(&mut info.crate_attrs, source, attr.span, &mut prev_span_hi);
                 }
             }
+            let mut has_non_module_items = false;
             for stmt in &body.stmts {
                 let mut is_extern_crate = false;
                 match stmt.kind {
                     StmtKind::Item(ref item) => {
                         is_extern_crate = check_item(&item, &mut info, crate_name);
                     }
-                    StmtKind::Expr(ref expr) if matches!(expr.kind, ast::ExprKind::Err(_)) => {
-                        reset_error_count(&psess);
-                        return Err(());
+                    StmtKind::Expr(ref expr) => {
+                        if matches!(expr.kind, ast::ExprKind::Err(_)) {
+                            reset_error_count(&psess);
+                            return Err(());
+                        }
+                        has_non_module_items = true;
                     }
                     StmtKind::MacCall(ref mac_call) if !info.has_main_fn => {
                         let mut iter = mac_call.mac.args.tokens.iter();
@@ -437,7 +441,11 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
                             }
                         }
                     }
-                    _ => {}
+                    // We do nothing in this case. Not marking it as `non_module_items` either.
+                    StmtKind::Empty => {}
+                    _ => {
+                        has_non_module_items = true;
+                    }
                 }
 
                 // Weirdly enough, the `Stmt` span doesn't include its attributes, so we need to
@@ -462,6 +470,11 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
                     push_to_s(&mut info.crates, source, span, &mut prev_span_hi);
                 }
             }
+            if has_non_module_items {
+                // FIXME: if `info.has_main_fn` is `true`, emit a warning here to mention that
+                // this code will not be called.
+                info.has_main_fn = false;
+            }
             Ok(info)
         }
         Err(e) => {

tests/rustdoc-ui/doctest/test-main-alongside-exprs.rs

@@ -0,0 +1,22 @@
+// This test ensures that if there is an expression alongside a `main`
+// function, it will not consider the entire code to be part of the `main`
+// function and will generate its own function to wrap everything.
+//
+// This is a regression test for:
+// * <https://github.com/rust-lang/rust/issues/140162>
+// * <https://github.com/rust-lang/rust/issues/139651>
+//@ compile-flags:--test
+//@ normalize-stdout: "tests/rustdoc-ui/doctest" -> "$$DIR"
+//@ normalize-stdout: "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ check-pass
+
+#![crate_name = "foo"]
+
+//! ```
+//! # if cfg!(miri) { return; }
+//! use std::ops::Deref;
+//!
+//! fn main() {
+//!     println!("Hi!");
+//! }
+//! ```

tests/rustdoc-ui/doctest/test-main-alongside-exprs.stdout

@@ -0,0 +1,6 @@
+
+running 1 test
+test $DIR/test-main-alongside-exprs.rs - (line 15) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+