rustdoc: Fix doctest heuristic for main fn wrapping

src/librustdoc/doctest/make.rs

@@ -301,8 +301,6 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
 
     let filename = FileName::anon_source_code(&wrapped_source);
 
-    // Any errors in parsing should also appear when the doctest is compiled for real, so just
-    // send all the errors that librustc_ast emits directly into a `Sink` instead of stderr.
     let sm = Arc::new(SourceMap::new(FilePathMapping::empty()));
     let fallback_bundle = rustc_errors::fallback_fluent_bundle(
         rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
@@ -311,7 +309,8 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
     info.supports_color =
         HumanEmitter::new(stderr_destination(ColorConfig::Auto), fallback_bundle.clone())
             .supports_color();
-
+    // Any errors in parsing should also appear when the doctest is compiled for real, so just
+    // send all the errors that the parser emits directly into a `Sink` instead of stderr.
     let emitter = HumanEmitter::new(Box::new(io::sink()), fallback_bundle);
 
     // FIXME(misdreavus): pass `-Z treat-err-as-bug` to the doctest parser
@@ -339,9 +338,6 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
         *prev_span_hi = hi;
     }
 
-    // Recurse through functions body. It is necessary because the doctest source code is
-    // wrapped in a function to limit the number of AST errors. If we don't recurse into
-    // functions, we would thing all top-level items (so basically nothing).
     fn check_item(item: &ast::Item, info: &mut ParseSourceInfo, crate_name: &Option<&str>) -> bool {
         let mut is_extern_crate = false;
         if !info.has_global_allocator
@@ -351,8 +347,6 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
         }
         match item.kind {
             ast::ItemKind::Fn(ref fn_item) if !info.has_main_fn => {
-                // We only push if it's the top item because otherwise, we would duplicate
-                // its content since the top-level item was already added.
                 if fn_item.ident.name == sym::main {
                     info.has_main_fn = true;
                 }
@@ -412,44 +406,41 @@ fn parse_source(source: &str, crate_name: &Option<&str>) -> Result<ParseSourceIn
                 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(());
-                        }
-                        has_non_items = true;
+                        is_extern_crate = check_item(item, &mut info, crate_name);
                     }
                     // We assume that the macro calls will expand to item(s) even though they could
-                    // expand to statements and expressions. And the simple fact that we're trying
-                    // to retrieve a `main` function inside it is a terrible idea.
+                    // expand to statements and expressions.
                     StmtKind::MacCall(ref mac_call) => {
-                        if info.has_main_fn {
-                            continue;
-                        }
-                        let mut iter = mac_call.mac.args.tokens.iter();
-
-                        while let Some(token) = iter.next() {
-                            if let TokenTree::Token(token, _) = token
-                                && let TokenKind::Ident(name, _) = token.kind
-                                && name == kw::Fn
-                                && let Some(TokenTree::Token(fn_token, _)) = iter.peek()
-                                && let TokenKind::Ident(fn_name, _) = fn_token.kind
-                                && fn_name == sym::main
-                                && let Some(TokenTree::Delimited(_, _, Delimiter::Parenthesis, _)) = {
-                                    iter.next();
-                                    iter.peek()
+                        if !info.has_main_fn {
+                            // For backward compatibility, we look for the token sequence `fn main(…)`
+                            // in the macro input (!) to crudely detect main functions "masked by a
+                            // wrapper macro". For the record, this is a horrible heuristic!
+                            // See <https://github.com/rust-lang/rust/issues/56898>.
+                            let mut iter = mac_call.mac.args.tokens.iter();
+                            while let Some(token) = iter.next() {
+                                if let TokenTree::Token(token, _) = token
+                                    && let TokenKind::Ident(kw::Fn, _) = token.kind
+                                    && let Some(TokenTree::Token(ident, _)) = iter.peek()
+                                    && let TokenKind::Ident(sym::main, _) = ident.kind
+                                    && let Some(TokenTree::Delimited(.., Delimiter::Parenthesis, _)) = {
+                                        iter.next();
+                                        iter.peek()
+                                    }
+                                {
+                                    info.has_main_fn = true;
+                                    break;
                                 }
-                            {
-                                info.has_main_fn = true;
-                                break;
                             }
                         }
                     }
-                    _ => {
+                    StmtKind::Expr(ref expr) => {
+                        if matches!(expr.kind, ast::ExprKind::Err(_)) {
+                            reset_error_count(&psess);
+                            return Err(());
+                        }
                         has_non_items = true;
                     }
+                    StmtKind::Let(_) | StmtKind::Semi(_) | StmtKind::Empty => has_non_items = true,
                 }
 
                 // Weirdly enough, the `Stmt` span doesn't include its attributes, so we need to

tests/rustdoc-ui/doctest/auxiliary/items.rs

@@ -0,0 +1 @@
+fn item() {}

tests/rustdoc-ui/doctest/main-alongside-macro-calls.fail.stdout

@@ -0,0 +1,60 @@
+
+running 4 tests
+test $DIR/main-alongside-macro-calls.rs - (line 19) ... ok
+test $DIR/main-alongside-macro-calls.rs - (line 24) ... ok
+test $DIR/main-alongside-macro-calls.rs - (line 28) ... FAILED
+test $DIR/main-alongside-macro-calls.rs - (line 33) ... FAILED
+
+failures:
+
+---- $DIR/main-alongside-macro-calls.rs - (line 28) stdout ----
+error: macros that expand to items must be delimited with braces or followed by a semicolon
+  --> $DIR/main-alongside-macro-calls.rs:30:1
+   |
+LL | println!();
+   | ^^^^^^^^^^
+   |
+   = note: this error originates in the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: macro expansion ignores `{` and any tokens following
+  --> $SRC_DIR/std/src/macros.rs:LL:COL
+   |
+  ::: $DIR/main-alongside-macro-calls.rs:30:1
+   |
+LL | println!();
+   | ---------- caused by the macro expansion here
+   |
+   = note: the usage of `print!` is likely invalid in item context
+
+error: aborting due to 2 previous errors
+
+Couldn't compile the test.
+---- $DIR/main-alongside-macro-calls.rs - (line 33) stdout ----
+error: macros that expand to items must be delimited with braces or followed by a semicolon
+  --> $DIR/main-alongside-macro-calls.rs:34:1
+   |
+LL | println!();
+   | ^^^^^^^^^^
+   |
+   = note: this error originates in the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: macro expansion ignores `{` and any tokens following
+  --> $SRC_DIR/std/src/macros.rs:LL:COL
+   |
+  ::: $DIR/main-alongside-macro-calls.rs:34:1
+   |
+LL | println!();
+   | ---------- caused by the macro expansion here
+   |
+   = note: the usage of `print!` is likely invalid in item context
+
+error: aborting due to 2 previous errors
+
+Couldn't compile the test.
+
+failures:
+    $DIR/main-alongside-macro-calls.rs - (line 28)
+    $DIR/main-alongside-macro-calls.rs - (line 33)
+
+test result: FAILED. 2 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+

tests/rustdoc-ui/doctest/main-alongside-macro-calls.pass.stdout

@@ -0,0 +1,9 @@
+
+running 4 tests
+test $DIR/main-alongside-macro-calls.rs - (line 19) ... ok
+test $DIR/main-alongside-macro-calls.rs - (line 24) ... ok
+test $DIR/main-alongside-macro-calls.rs - (line 28) - compile fail ... ok
+test $DIR/main-alongside-macro-calls.rs - (line 33) - compile fail ... ok
+
+test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+

tests/rustdoc-ui/doctest/main-alongside-macro-calls.rs

@@ -0,0 +1,44 @@
+// This test ensures that if there is are any macro calls alongside a `main` function,
+// it will indeed consider the `main` function as the program entry point and *won't*
+// generate its own `main` function to wrap everything even though macro calls are
+// valid in statement contexts, too, and could just as well expand to statements or
+// expressions (we don't perform any macro expansion to find `main`, see also
+// <https://github.com/rust-lang/rust/issues/57415>).
+//
+// See <./main-alongside-stmts.rs> for comparison.
+//
+//@ compile-flags:--test --test-args --test-threads=1
+//@ normalize-stdout: "tests/rustdoc-ui/doctest" -> "$$DIR"
+//@ normalize-stdout: "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ revisions: pass fail
+//@[pass] check-pass
+//@[fail] failure-status: 101
+
+// Regression test for <https://github.com/rust-lang/rust/pull/140220#issuecomment-2831872920>:
+
+//! ```
+//! fn main() {}
+//! include!("./auxiliary/items.rs");
+//! ```
+//!
+//! ```
+//! include!("./auxiliary/items.rs");
+//! fn main() {}
+//! ```
+
+// Regression test for <https://github.com/rust-lang/rust/issues/140412>:
+// We test the "same" thing twice: Once via `compile_fail` to more closely mirror the reported
+// regression and once without it to make sure that it leads to the expected rustc errors,
+// namely `println!(…)` not being valid in item contexts.
+
+#![cfg_attr(pass, doc = " ```compile_fail")]
+#![cfg_attr(fail, doc = " ```")]
+//! fn main() {}
+//! println!();
+//! ```
+//!
+#![cfg_attr(pass, doc = " ```compile_fail")]
+#![cfg_attr(fail, doc = " ```")]
+//! println!();
+//! fn main() {}
+//! ```

tests/rustdoc-ui/doctest/main-alongside-stmts.rs

@@ -0,0 +1,33 @@
+// This test ensures that if there is are any statements alongside a `main` function,
+// it will not consider the `main` function as the program entry point but instead
+// will generate its own `main` function to wrap everything as it needs to reside in a
+// module where only *items* are permitted syntactically.
+//
+// See <./main-alongside-macro-calls.rs> for comparison.
+//
+// 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 --test-args --test-threads=1
+//@ normalize-stdout: "tests/rustdoc-ui/doctest" -> "$$DIR"
+//@ normalize-stdout: "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ check-pass
+
+//! ```
+//! # if cfg!(miri) { return; }
+//! use std::ops::Deref;
+//!
+//! fn main() {
+//!     assert!(false);
+//! }
+//! ```
+//!
+//! ```
+//! let x = 2;
+//! assert_eq!(x, 2);
+//!
+//! fn main() {
+//!     assert!(false);
+//! }
+//! ```

tests/rustdoc-ui/doctest/main-alongside-stmts.stdout

@@ -0,0 +1,7 @@
+
+running 2 tests
+test $DIR/main-alongside-stmts.rs - (line 17) ... ok
+test $DIR/main-alongside-stmts.rs - (line 26) ... ok
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+