Rollup merge of #69838 - Centril:expand-module, r=petrochenkov

Expansion-driven outline module parsing

After this PR, the parser will not do any conditional compilation or loading of external module files when `mod foo;` is encountered. Instead, the parser only leaves `mod foo;` in place in the AST, with no items filled in. Expansion later kicks in and will load the actual files and do the parsing. This entails that the following is now valid:

```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

Fixes https://github.com/rust-lang/rust/issues/64197.

r? @petrochenkov

1 files changed, 5 insertions, 46 deletions

diff --git a/src/librustc_parse/lib.rs b/src/librustc_parse/lib.rs
index 884499ff2dd..c31cc1b4c9f 100644
--- a/src/librustc_parse/lib.rs
+++ b/src/librustc_parse/lib.rs
@@ -3,6 +3,7 @@
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
 #![feature(bindings_after_at)]
+#![feature(try_blocks)]
 
 use rustc_ast::ast;
 use rustc_ast::token::{self, Nonterminal};
@@ -13,7 +14,7 @@ use rustc_errors::{Diagnostic, FatalError, Level, PResult};
 use rustc_session::parse::ParseSess;
 use rustc_span::{FileName, SourceFile, Span};
 
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::str;
 
 use log::info;
@@ -25,24 +26,6 @@ pub mod parser;
 use parser::{emit_unclosed_delims, make_unclosed_delims_error, Parser};
 pub mod lexer;
 pub mod validate_attr;
-#[macro_use]
-pub mod config;
-
-#[derive(Clone)]
-pub struct Directory {
-    pub path: PathBuf,
-    pub ownership: DirectoryOwnership,
-}
-
-#[derive(Copy, Clone)]
-pub enum DirectoryOwnership {
-    Owned {
-        // None if `mod.rs`, `Some("foo")` if we're in `foo.rs`.
-        relative: Option<ast::Ident>,
-    },
-    UnownedViaBlock,
-    UnownedViaMod,
-}
 
 // A bunch of utility functions of the form `parse_<thing>_from_<source>`
 // where <thing> includes crate, expr, item, stmt, tts, and one that
@@ -119,10 +102,7 @@ pub fn maybe_new_parser_from_source_str(
     name: FileName,
     source: String,
 ) -> Result<Parser<'_>, Vec<Diagnostic>> {
-    let mut parser =
-        maybe_source_file_to_parser(sess, sess.source_map().new_source_file(name, source))?;
-    parser.recurse_into_file_modules = false;
-    Ok(parser)
+    maybe_source_file_to_parser(sess, sess.source_map().new_source_file(name, source))
 }
 
 /// Creates a new parser, handling errors as appropriate if the file doesn't exist.
@@ -146,12 +126,10 @@ pub fn maybe_new_parser_from_file<'a>(
 pub fn new_sub_parser_from_file<'a>(
     sess: &'a ParseSess,
     path: &Path,
-    directory_ownership: DirectoryOwnership,
     module_name: Option<String>,
     sp: Span,
 ) -> Parser<'a> {
     let mut p = source_file_to_parser(sess, file_to_source_file(sess, path, Some(sp)));
-    p.directory.ownership = directory_ownership;
     p.root_module_name = module_name;
     p
 }
@@ -257,26 +235,7 @@ pub fn stream_to_parser<'a>(
     stream: TokenStream,
     subparser_name: Option<&'static str>,
 ) -> Parser<'a> {
-    Parser::new(sess, stream, None, true, false, subparser_name)
-}
-
-/// Given a stream, the `ParseSess` and the base directory, produces a parser.
-///
-/// Use this function when you are creating a parser from the token stream
-/// and also care about the current working directory of the parser (e.g.,
-/// you are trying to resolve modules defined inside a macro invocation).
-///
-/// # Note
-///
-/// The main usage of this function is outside of rustc, for those who uses
-/// librustc_ast as a library. Please do not remove this function while refactoring
-/// just because it is not used in rustc codebase!
-pub fn stream_to_parser_with_base_dir(
-    sess: &ParseSess,
-    stream: TokenStream,
-    base_dir: Directory,
-) -> Parser<'_> {
-    Parser::new(sess, stream, Some(base_dir), true, false, None)
+    Parser::new(sess, stream, false, subparser_name)
 }
 
 /// Runs the given subparser `f` on the tokens of the given `attr`'s item.
@@ -286,7 +245,7 @@ pub fn parse_in<'a, T>(
     name: &'static str,
     mut f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,
 ) -> PResult<'a, T> {
-    let mut parser = Parser::new(sess, tts, None, false, false, Some(name));
+    let mut parser = Parser::new(sess, tts, false, Some(name));
     let result = f(&mut parser)?;
     if parser.token != token::Eof {
         parser.unexpected()?;