Stop using DiagnosticBuilder::buffer in the parser.

One consequence is that errors returned by
`maybe_new_parser_from_source_str` now must be consumed, so a bunch of
places that previously ignored those errors now cancel them. (Most of
them explicitly dropped the errors before. I guess that was to indicate
"we are explicitly ignoring these", though I'm not 100% sure.)

compiler/rustc_interface/src/interface.rs

@@ -82,7 +82,7 @@ pub(crate) fn parse_cfg(dcx: &DiagCtxt, cfgs: Vec<String>) -> Cfg {
                     Ok(..) => {}
                     Err(err) => err.cancel(),
                 },
-                Err(errs) => drop(errs),
+                Err(errs) => errs.into_iter().for_each(|err| err.cancel()),
             }
 
             // If the user tried to use a key="value" flag, but is missing the quotes, provide
@@ -129,9 +129,12 @@ pub(crate) fn parse_check_cfg(dcx: &DiagCtxt, specs: Vec<String>) -> CheckCfg {
             error!("expected `cfg(name, values(\"value1\", \"value2\", ... \"valueN\"))`")
         };
 
-        let Ok(mut parser) = maybe_new_parser_from_source_str(&sess, filename, s.to_string())
-        else {
-            expected_error();
+        let mut parser = match maybe_new_parser_from_source_str(&sess, filename, s.to_string()) {
+            Ok(parser) => parser,
+            Err(errs) => {
+                errs.into_iter().for_each(|err| err.cancel());
+                expected_error();
+            }
         };
 
         let meta_item = match parser.parse_meta_item() {

compiler/rustc_parse/src/lexer/mod.rs

@@ -7,7 +7,7 @@ use rustc_ast::ast::{self, AttrStyle};
 use rustc_ast::token::{self, CommentKind, Delimiter, Token, TokenKind};
 use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::util::unicode::contains_text_flow_control_chars;
-use rustc_errors::{error_code, Applicability, DiagCtxt, Diagnostic, StashKey};
+use rustc_errors::{error_code, Applicability, DiagCtxt, DiagnosticBuilder, StashKey};
 use rustc_lexer::unescape::{self, EscapeError, Mode};
 use rustc_lexer::{Base, DocStyle, RawStrError};
 use rustc_lexer::{Cursor, LiteralKind};
@@ -47,7 +47,7 @@ pub(crate) fn parse_token_trees<'sess, 'src>(
     mut src: &'src str,
     mut start_pos: BytePos,
     override_span: Option<Span>,
-) -> Result<TokenStream, Vec<Diagnostic>> {
+) -> Result<TokenStream, Vec<DiagnosticBuilder<'sess>>> {
     // Skip `#!`, if present.
     if let Some(shebang_len) = rustc_lexer::strip_shebang(src) {
         src = &src[shebang_len..];
@@ -76,13 +76,13 @@ pub(crate) fn parse_token_trees<'sess, 'src>(
             let mut buffer = Vec::with_capacity(1);
             for unmatched in unmatched_delims {
                 if let Some(err) = make_unclosed_delims_error(unmatched, sess) {
-                    err.buffer(&mut buffer);
+                    buffer.push(err);
                 }
             }
             if let Err(errs) = res {
                 // Add unclosing delimiter or diff marker errors
                 for err in errs {
-                    err.buffer(&mut buffer);
+                    buffer.push(err);
                 }
             }
             Err(buffer)

compiler/rustc_parse/src/lib.rs

@@ -19,7 +19,7 @@ use rustc_ast::tokenstream::TokenStream;
 use rustc_ast::{AttrItem, Attribute, MetaItem};
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Diagnostic, PResult};
+use rustc_errors::{DiagnosticBuilder, FatalError, PResult};
 use rustc_session::parse::ParseSess;
 use rustc_span::{FileName, SourceFile, Span};
 
@@ -45,14 +45,13 @@ rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
 /// A variant of 'panictry!' that works on a `Vec<Diagnostic>` instead of a single
 /// `DiagnosticBuilder`.
 macro_rules! panictry_buffer {
-    ($handler:expr, $e:expr) => {{
-        use rustc_errors::FatalError;
+    ($e:expr) => {{
         use std::result::Result::{Err, Ok};
         match $e {
             Ok(e) => e,
             Err(errs) => {
                 for e in errs {
-                    $handler.emit_diagnostic(e);
+                    e.emit();
                 }
                 FatalError.raise()
             }
@@ -100,16 +99,17 @@ pub fn parse_stream_from_source_str(
 
 /// Creates a new parser from a source string.
 pub fn new_parser_from_source_str(sess: &ParseSess, name: FileName, source: String) -> Parser<'_> {
-    panictry_buffer!(&sess.dcx, maybe_new_parser_from_source_str(sess, name, source))
+    panictry_buffer!(maybe_new_parser_from_source_str(sess, name, source))
 }
 
 /// Creates a new parser from a source string. Returns any buffered errors from lexing the initial
-/// token stream.
+/// token stream; these must be consumed via `emit`, `cancel`, etc., otherwise a panic will occur
+/// when they are dropped.
 pub fn maybe_new_parser_from_source_str(
     sess: &ParseSess,
     name: FileName,
     source: String,
-) -> Result<Parser<'_>, Vec<Diagnostic>> {
+) -> Result<Parser<'_>, Vec<DiagnosticBuilder<'_>>> {
     maybe_source_file_to_parser(sess, sess.source_map().new_source_file(name, source))
 }
 
@@ -125,7 +125,7 @@ pub fn new_parser_from_file<'a>(sess: &'a ParseSess, path: &Path, sp: Option<Spa
         err.emit();
     });
 
-    panictry_buffer!(&sess.dcx, maybe_source_file_to_parser(sess, source_file))
+    panictry_buffer!(maybe_source_file_to_parser(sess, source_file))
 }
 
 /// Given a session and a `source_file`, return a parser. Returns any buffered errors from lexing
@@ -133,7 +133,7 @@ pub fn new_parser_from_file<'a>(sess: &'a ParseSess, path: &Path, sp: Option<Spa
 fn maybe_source_file_to_parser(
     sess: &ParseSess,
     source_file: Lrc<SourceFile>,
-) -> Result<Parser<'_>, Vec<Diagnostic>> {
+) -> Result<Parser<'_>, Vec<DiagnosticBuilder<'_>>> {
     let end_pos = source_file.end_position();
     let stream = maybe_file_to_stream(sess, source_file, None)?;
     let mut parser = stream_to_parser(sess, stream, None);
@@ -152,16 +152,16 @@ pub fn source_file_to_stream(
     source_file: Lrc<SourceFile>,
     override_span: Option<Span>,
 ) -> TokenStream {
-    panictry_buffer!(&sess.dcx, maybe_file_to_stream(sess, source_file, override_span))
+    panictry_buffer!(maybe_file_to_stream(sess, source_file, override_span))
 }
 
 /// Given a source file, produces a sequence of token trees. Returns any buffered errors from
 /// parsing the token stream.
-fn maybe_file_to_stream(
-    sess: &ParseSess,
+fn maybe_file_to_stream<'sess>(
+    sess: &'sess ParseSess,
     source_file: Lrc<SourceFile>,
     override_span: Option<Span>,
-) -> Result<TokenStream, Vec<Diagnostic>> {
+) -> Result<TokenStream, Vec<DiagnosticBuilder<'sess>>> {
     let src = source_file.src.as_ref().unwrap_or_else(|| {
         sess.dcx.bug(format!(
             "cannot lex `source_file` without source: {}",

src/librustdoc/clean/render_macro_matchers.rs

@@ -69,8 +69,8 @@ fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String
     let mut parser =
         match rustc_parse::maybe_new_parser_from_source_str(&sess, file_name, snippet.clone()) {
             Ok(parser) => parser,
-            Err(diagnostics) => {
-                drop(diagnostics);
+            Err(errs) => {
+                errs.into_iter().for_each(|err| err.cancel());
                 return None;
             }
         };

src/librustdoc/doctest.rs

@@ -589,7 +589,7 @@ pub(crate) fn make_test(
             let mut parser = match maybe_new_parser_from_source_str(&sess, filename, source) {
                 Ok(p) => p,
                 Err(errs) => {
-                    drop(errs);
+                    errs.into_iter().for_each(|err| err.cancel());
                     return (found_main, found_extern_crate, found_macro);
                 }
             };
@@ -759,8 +759,10 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
             let mut parser =
                 match maybe_new_parser_from_source_str(&sess, filename, source.to_owned()) {
                     Ok(p) => p,
-                    Err(_) => {
-                        // If there is an unclosed delimiter, an error will be returned by the tokentrees.
+                    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;
                     }
                 };

src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs

@@ -53,7 +53,7 @@ pub fn check(
                 let mut parser = match maybe_new_parser_from_source_str(&sess, filename, code) {
                     Ok(p) => p,
                     Err(errs) => {
-                        drop(errs);
+                        errs.into_iter().for_each(|err| err.cancel());
                         return (false, test_attr_spans);
                     },
                 };

src/tools/rustfmt/src/parse/parser.rs

@@ -3,7 +3,7 @@ use std::path::{Path, PathBuf};
 
 use rustc_ast::token::TokenKind;
 use rustc_ast::{ast, attr, ptr};
-use rustc_errors::Diagnostic;
+use rustc_errors::DiagnosticBuilder;
 use rustc_parse::{new_parser_from_file, parser::Parser as RawParser};
 use rustc_span::{sym, Span};
 use thin_vec::ThinVec;
@@ -65,7 +65,7 @@ impl<'a> ParserBuilder<'a> {
     fn parser(
         sess: &'a rustc_session::parse::ParseSess,
         input: Input,
-    ) -> Result<rustc_parse::parser::Parser<'a>, Option<Vec<Diagnostic>>> {
+    ) -> Result<rustc_parse::parser::Parser<'a>, Option<Vec<DiagnosticBuilder<'a>>>> {
         match input {
             Input::File(ref file) => catch_unwind(AssertUnwindSafe(move || {
                 new_parser_from_file(sess, file, None)

src/tools/rustfmt/src/parse/session.rs

@@ -4,7 +4,9 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use rustc_data_structures::sync::{IntoDynSyncSend, Lrc};
 use rustc_errors::emitter::{DynEmitter, Emitter, HumanEmitter};
 use rustc_errors::translation::Translate;
-use rustc_errors::{ColorConfig, DiagCtxt, Diagnostic, Level as DiagnosticLevel};
+use rustc_errors::{
+    ColorConfig, DiagCtxt, Diagnostic, DiagnosticBuilder, Level as DiagnosticLevel,
+};
 use rustc_session::parse::ParseSess as RawParseSess;
 use rustc_span::{
     source_map::{FilePathMapping, SourceMap},
@@ -283,9 +285,9 @@ impl ParseSess {
 
 // Methods that should be restricted within the parse module.
 impl ParseSess {
-    pub(super) fn emit_diagnostics(&self, diagnostics: Vec<Diagnostic>) {
+    pub(super) fn emit_diagnostics(&self, diagnostics: Vec<DiagnosticBuilder<'_>>) {
         for diagnostic in diagnostics {
-            self.parse_sess.dcx.emit_diagnostic(diagnostic);
+            diagnostic.emit();
         }
     }