Rollup merge of #129667 - dev-ardi:rustc_driver-cleanup, r=michaelwoerister

Rustc driver cleanup

This adds a few comments to the driver to clarify a bit what's happening and does some cleanup.

compiler/rustc_driver_impl/src/lib.rs

@@ -393,13 +393,17 @@ fn run_compiler(
 
         let linker = compiler.enter(|queries| {
             let early_exit = || early_exit().map(|_| None);
+
+            // Parse the crate root source code (doesn't parse submodules yet)
+            // Everything else is parsed during macro expansion.
             queries.parse()?;
 
-            if let Some(ppm) = &sess.opts.pretty {
-                if ppm.needs_ast_map() {
+            // If pretty printing is requested: Figure out the representation, print it and exit
+            if let Some(pp_mode) = sess.opts.pretty {
+                if pp_mode.needs_ast_map() {
                     queries.global_ctxt()?.enter(|tcx| {
                         tcx.ensure().early_lint_checks(());
-                        pretty::print(sess, *ppm, pretty::PrintExtra::NeedsAstMap { tcx });
+                        pretty::print(sess, pp_mode, pretty::PrintExtra::NeedsAstMap { tcx });
                         Ok(())
                     })?;
 
@@ -410,7 +414,7 @@ fn run_compiler(
                     let krate = queries.parse()?;
                     pretty::print(
                         sess,
-                        *ppm,
+                        pp_mode,
                         pretty::PrintExtra::AfterParsing { krate: &*krate.borrow() },
                     );
                 }
@@ -465,12 +469,8 @@ fn run_compiler(
             linker.link(sess, codegen_backend)?
         }
 
-        if sess.opts.unstable_opts.print_fuel.is_some() {
-            eprintln!(
-                "Fuel used by {}: {}",
-                sess.opts.unstable_opts.print_fuel.as_ref().unwrap(),
-                sess.print_fuel.load(Ordering::SeqCst)
-            );
+        if let Some(fuel) = sess.opts.unstable_opts.print_fuel.as_deref() {
+            eprintln!("Fuel used by {}: {}", fuel, sess.print_fuel.load(Ordering::SeqCst));
         }
 
         Ok(())
@@ -487,36 +487,43 @@ fn make_output(matches: &getopts::Matches) -> (Option<PathBuf>, Option<OutFileNa
     (odir, ofile)
 }
 
-// Extract input (string or file and optional path) from matches.
+/// Extract input (string or file and optional path) from matches.
+/// This handles reading from stdin if `-` is provided.
 fn make_input(
     early_dcx: &EarlyDiagCtxt,
     free_matches: &[String],
 ) -> Result<Option<Input>, ErrorGuaranteed> {
-    let [ifile] = free_matches else { return Ok(None) };
-    if ifile == "-" {
-        let mut src = String::new();
-        if io::stdin().read_to_string(&mut src).is_err() {
+    let [input_file] = free_matches else { return Ok(None) };
+
+    if input_file != "-" {
+        // Normal `Input::File`
+        return Ok(Some(Input::File(PathBuf::from(input_file))));
+    }
+
+    // read from stdin as `Input::Str`
+    let mut input = String::new();
+    if io::stdin().read_to_string(&mut input).is_err() {
         // Immediately stop compilation if there was an issue reading
         // the input (for example if the input stream is not UTF-8).
         let reported =
             early_dcx.early_err("couldn't read from stdin, as it did not contain valid UTF-8");
         return Err(reported);
     }
-        if let Ok(path) = env::var("UNSTABLE_RUSTDOC_TEST_PATH") {
+
+    let name = match env::var("UNSTABLE_RUSTDOC_TEST_PATH") {
+        Ok(path) => {
             let line = env::var("UNSTABLE_RUSTDOC_TEST_LINE").expect(
                 "when UNSTABLE_RUSTDOC_TEST_PATH is set \
                                     UNSTABLE_RUSTDOC_TEST_LINE also needs to be set",
             );
             let line = isize::from_str_radix(&line, 10)
                 .expect("UNSTABLE_RUSTDOC_TEST_LINE needs to be an number");
-            let file_name = FileName::doc_test_source_code(PathBuf::from(path), line);
-            Ok(Some(Input::Str { name: file_name, input: src }))
-        } else {
-            Ok(Some(Input::Str { name: FileName::anon_source_code(&src), input: src }))
-        }
-    } else {
-        Ok(Some(Input::File(PathBuf::from(ifile))))
+            FileName::doc_test_source_code(PathBuf::from(path), line)
         }
+        Err(_) => FileName::anon_source_code(&input),
+    };
+
+    Ok(Some(Input::Str { name, input }))
 }
 
 /// Whether to stop or continue compilation.

compiler/rustc_parse/src/parser/item.rs

@@ -51,7 +51,9 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses the contents of a module (inner attributes followed by module items).
-    /// We exit once we hit `term`
+    /// We exit once we hit `term` which can be either
+    /// - EOF (for files)
+    /// - `}` for mod items
     pub fn parse_mod(
         &mut self,
         term: &TokenKind,

compiler/rustc_session/src/config.rs

@@ -2893,6 +2893,7 @@ pub enum PpHirMode {
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]
+/// Pretty print mode
 pub enum PpMode {
     /// Options that print the source code, i.e.
     /// `-Zunpretty=normal` and `-Zunpretty=expanded`