Rollup merge of #125815 - nnethercote:rustc_parse-top-level-cleanups, r=spastorino

`rustc_parse` top-level cleanups

A bunch of improvements in and around `compiler/rustc_parse/src/lib.rs`. Many of the changes streamline the API in that file from this (12 functions and one macro):
```
    name                              args                  return type
    ----                              ----                  -----------
    panictry_buffer!                  Result<T, Vec<Diag>>  T

pub parse_crate_from_file             path                  PResult<Crate>
pub parse_crate_attrs_from_file       path                  PResult<AttrVec>
pub parse_crate_from_source_str       name,src              PResult<Crate>
pub parse_crate_attrs_from_source_str name,src              PResult<AttrVec>

pub new_parser_from_source_str        name,src              Parser
pub maybe_new_parser_from_source_str  name,src              Result<Parser, Vec<Diag>>
pub new_parser_from_file              path,error_sp         Parser
    maybe_source_file_to_parser       srcfile               Result<Parser, Vec<Diag>>

pub parse_stream_from_source_str      name,src,override_sp  TokenStream
pub source_file_to_stream             srcfile,override_sp   TokenStream
    maybe_file_to_stream              srcfile,override_sp   Result<TokenStream, Vec<Diag>>

pub stream_to_parser                  stream,subparser_name Parser
```
to this:
```
    name                              args                  return type
    ----                              ----                  -----------
    unwrap_or_emit_fatal              Result<T, Vec<Diag>>  T

pub new_parser_from_source_str        name,src              Result<Parser, Vec<Diag>>
pub new_parser_from_file              path,error_sp         Result<Parser, Vec<Diag>>
    new_parser_from_source_file       srcfile               Result<Parser, Vec<Diag>>

pub source_str_to_stream              name,src,override_sp  Result<TokenStream, Vec<Diag>>
    source_file_to_stream             srcfile,override_sp   Result<TokenStream, Vec<Diag>>
```
I found the old API quite confusing, with lots of similar-sounding function names and no clear structure. I think the new API is much better.

r? `@spastorino`

6 files changed, 31 insertions, 37 deletions

diff --git a/src/librustdoc/clean/render_macro_matchers.rs b/src/librustdoc/clean/render_macro_matchers.rs
index 5ac1b742c38..995919f73f8 100644
--- a/src/librustdoc/clean/render_macro_matchers.rs
+++ b/src/librustdoc/clean/render_macro_matchers.rs
@@ -65,7 +65,7 @@ fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String
     let psess = ParseSess::new(rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec());
     let file_name = source_map.span_to_filename(span);
     let mut parser =
-        match rustc_parse::maybe_new_parser_from_source_str(&psess, file_name, snippet.clone()) {
+        match rustc_parse::new_parser_from_source_str(&psess, file_name, snippet.clone()) {
             Ok(parser) => parser,
             Err(errs) => {
                 errs.into_iter().for_each(|err| err.cancel());
diff --git a/src/librustdoc/doctest.rs b/src/librustdoc/doctest.rs
index a536a713921..0d4bad6921d 100644
--- a/src/librustdoc/doctest.rs
+++ b/src/librustdoc/doctest.rs
@@ -9,7 +9,7 @@ use rustc_interface::interface;
 use rustc_middle::hir::map::Map;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::TyCtxt;
-use rustc_parse::maybe_new_parser_from_source_str;
+use rustc_parse::new_parser_from_source_str;
 use rustc_parse::parser::attr::InnerAttrPolicy;
 use rustc_resolve::rustdoc::span_of_fragments;
 use rustc_session::config::{self, CrateType, ErrorOutputType};
@@ -638,7 +638,7 @@ pub(crate) fn make_test(
             let mut found_extern_crate = crate_name.is_none();
             let mut found_macro = false;
 
-            let mut parser = match maybe_new_parser_from_source_str(&psess, filename, source) {
+            let mut parser = match new_parser_from_source_str(&psess, filename, source) {
                 Ok(p) => p,
                 Err(errs) => {
                     errs.into_iter().for_each(|err| err.cancel());
@@ -818,16 +818,15 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
 
             let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
             let psess = ParseSess::with_dcx(dcx, sm);
-            let mut parser =
-                match maybe_new_parser_from_source_str(&psess, filename, source.to_owned()) {
-                    Ok(p) => p,
-                    Err(errs) => {
-                        errs.into_iter().for_each(|err| err.cancel());
-                        // If there is an unclosed delimiter, an error will be returned by the
-                        // tokentrees.
-                        return false;
-                    }
-                };
+            let mut parser = match new_parser_from_source_str(&psess, filename, source.to_owned()) {
+                Ok(p) => p,
+                Err(errs) => {
+                    errs.into_iter().for_each(|err| err.cancel());
+                    // If there is an unclosed delimiter, an error will be returned by the
+                    // tokentrees.
+                    return false;
+                }
+            };
             // If a parsing error happened, it's very likely that the attribute is incomplete.
             if let Err(e) = parser.parse_attribute(InnerAttrPolicy::Permitted) {
                 e.cancel();
diff --git a/src/librustdoc/passes/lint/check_code_block_syntax.rs b/src/librustdoc/passes/lint/check_code_block_syntax.rs
index 39350f4cbbb..c185442fd55 100644
--- a/src/librustdoc/passes/lint/check_code_block_syntax.rs
+++ b/src/librustdoc/passes/lint/check_code_block_syntax.rs
@@ -5,7 +5,7 @@ use rustc_errors::{
     translation::{to_fluent_args, Translate},
     Applicability, DiagCtxt, DiagInner, LazyFallbackBundle,
 };
-use rustc_parse::parse_stream_from_source_str;
+use rustc_parse::{source_str_to_stream, unwrap_or_emit_fatal};
 use rustc_resolve::rustdoc::source_span_for_markdown_range;
 use rustc_session::parse::ParseSess;
 use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId, Transparency};
@@ -51,12 +51,12 @@ fn check_rust_syntax(
     let span = DUMMY_SP.apply_mark(expn_id.to_expn_id(), Transparency::Transparent);
 
     let is_empty = rustc_driver::catch_fatal_errors(|| {
-        parse_stream_from_source_str(
+        unwrap_or_emit_fatal(source_str_to_stream(
+            &psess,
             FileName::Custom(String::from("doctest")),
             source,
-            &psess,
             Some(span),
-        )
+        ))
         .is_empty()
     })
     .unwrap_or(false);
diff --git a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
index 651f2ebaee6..c3e3c0431e6 100644
--- a/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
+++ b/src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
@@ -8,7 +8,7 @@ use rustc_data_structures::sync::Lrc;
 use rustc_errors::emitter::HumanEmitter;
 use rustc_errors::{Diag, DiagCtxt};
 use rustc_lint::LateContext;
-use rustc_parse::maybe_new_parser_from_source_str;
+use rustc_parse::new_parser_from_source_str;
 use rustc_parse::parser::ForceCollect;
 use rustc_session::parse::ParseSess;
 use rustc_span::edition::Edition;
@@ -50,7 +50,7 @@ pub fn check(
                 let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
                 let psess = ParseSess::with_dcx(dcx, sm);
 
-                let mut parser = match maybe_new_parser_from_source_str(&psess, filename, code) {
+                let mut parser = match new_parser_from_source_str(&psess, filename, code) {
                     Ok(p) => p,
                     Err(errs) => {
                         errs.into_iter().for_each(Diag::cancel);
diff --git a/src/tools/rustfmt/src/parse/macros/mod.rs b/src/tools/rustfmt/src/parse/macros/mod.rs
index 3cf133c647c..cbcc0b2d636 100644
--- a/src/tools/rustfmt/src/parse/macros/mod.rs
+++ b/src/tools/rustfmt/src/parse/macros/mod.rs
@@ -2,7 +2,7 @@ use rustc_ast::token::{Delimiter, NonterminalKind, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{ast, ptr};
 use rustc_parse::parser::{ForceCollect, Parser, Recovery};
-use rustc_parse::{stream_to_parser, MACRO_ARGUMENTS};
+use rustc_parse::MACRO_ARGUMENTS;
 use rustc_session::parse::ParseSess;
 use rustc_span::symbol::{self, kw};
 use rustc_span::Symbol;
@@ -15,7 +15,7 @@ pub(crate) mod cfg_if;
 pub(crate) mod lazy_static;
 
 fn build_stream_parser<'a>(psess: &'a ParseSess, tokens: TokenStream) -> Parser<'a> {
-    stream_to_parser(psess, tokens, MACRO_ARGUMENTS).recovery(Recovery::Forbidden)
+    Parser::new(psess, tokens, MACRO_ARGUMENTS).recovery(Recovery::Forbidden)
 }
 
 fn build_parser<'a>(context: &RewriteContext<'a>, tokens: TokenStream) -> Parser<'a> {
diff --git a/src/tools/rustfmt/src/parse/parser.rs b/src/tools/rustfmt/src/parse/parser.rs
index 5dcdca1d953..6051241309d 100644
--- a/src/tools/rustfmt/src/parse/parser.rs
+++ b/src/tools/rustfmt/src/parse/parser.rs
@@ -4,7 +4,8 @@ use std::path::{Path, PathBuf};
 use rustc_ast::token::TokenKind;
 use rustc_ast::{ast, attr, ptr};
 use rustc_errors::Diag;
-use rustc_parse::{new_parser_from_file, parser::Parser as RawParser};
+use rustc_parse::parser::Parser as RawParser;
+use rustc_parse::{new_parser_from_file, new_parser_from_source_str, unwrap_or_emit_fatal};
 use rustc_span::{sym, Span};
 use thin_vec::ThinVec;
 
@@ -50,12 +51,9 @@ impl<'a> ParserBuilder<'a> {
 
         let parser = match Self::parser(psess.inner(), input) {
             Ok(p) => p,
-            Err(db) => {
-                if let Some(diagnostics) = db {
-                    psess.emit_diagnostics(diagnostics);
-                    return Err(ParserError::ParserCreationError);
-                }
-                return Err(ParserError::ParsePanicError);
+            Err(diagnostics) => {
+                psess.emit_diagnostics(diagnostics);
+                return Err(ParserError::ParserCreationError);
             }
         };
 
@@ -65,18 +63,14 @@ impl<'a> ParserBuilder<'a> {
     fn parser(
         psess: &'a rustc_session::parse::ParseSess,
         input: Input,
-    ) -> Result<rustc_parse::parser::Parser<'a>, Option<Vec<Diag<'a>>>> {
+    ) -> Result<RawParser<'a>, Vec<Diag<'a>>> {
         match input {
-            Input::File(ref file) => catch_unwind(AssertUnwindSafe(move || {
-                new_parser_from_file(psess, file, None)
-            }))
-            .map_err(|_| None),
-            Input::Text(text) => rustc_parse::maybe_new_parser_from_source_str(
+            Input::File(ref file) => new_parser_from_file(psess, file, None),
+            Input::Text(text) => new_parser_from_source_str(
                 psess,
                 rustc_span::FileName::Custom("stdin".to_owned()),
                 text,
-            )
-            .map_err(Some),
+            ),
         }
     }
 }
@@ -111,7 +105,8 @@ impl<'a> Parser<'a> {
         span: Span,
     ) -> Result<(ast::AttrVec, ThinVec<ptr::P<ast::Item>>, Span), ParserError> {
         let result = catch_unwind(AssertUnwindSafe(|| {
-            let mut parser = new_parser_from_file(psess.inner(), path, Some(span));
+            let mut parser =
+                unwrap_or_emit_fatal(new_parser_from_file(psess.inner(), path, Some(span)));
             match parser.parse_mod(&TokenKind::Eof) {
                 Ok((a, i, spans)) => Some((a, i, spans.inner_span)),
                 Err(e) => {