mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Make top-level rustc_parse functions fallible.

Browse Source 
Currently we have an awkward mix of fallible and infallible functions:
```
       new_parser_from_source_str
 maybe_new_parser_from_source_str
       new_parser_from_file
(maybe_new_parser_from_file)        // missing
      (new_parser_from_source_file) // missing
 maybe_new_parser_from_source_file
       source_str_to_stream
 maybe_source_file_to_stream
```
We could add the two missing functions, but instead this commit removes
of all the infallible ones and renames the fallible ones leaving us with
these which are all fallible:
```
new_parser_from_source_str
new_parser_from_file
new_parser_from_source_file
source_str_to_stream
source_file_to_stream
```
This requires making `unwrap_or_emit_fatal` public so callers of
formerly infallible functions can still work.

This does make some of the call sites slightly more verbose, but I think
it's worth it for the simpler API. Also, there are two `catch_unwind`
calls and one `catch_fatal_errors` call in this diff that become
removable thanks this change. (I will do that in a follow-up PR.)
This commit is contained in:
Nicholas Nethercote 2024-05-31 15:43:18 +10:00
parent 264dbe4d81
commit b9037339cb
16 changed files with 105 additions and 75 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
compiler/rustc_builtin_macros/src/cmdline_attrs.rs
View File

@ -4,16 +4,17 @@
use rustc_ast::attr::mk_attr;
use rustc_ast::token;
use rustc_ast::{self as ast, AttrItem, AttrStyle};
use rustc_parse::{new_parser_from_source_str, unwrap_or_emit_fatal};
use rustc_session::parse::ParseSess;
use rustc_span::FileName;
pub fn inject(krate: &mut ast::Crate, psess: &ParseSess, attrs: &[String]) {
for raw_attr in attrs {
let mut parser = rustc_parse::new_parser_from_source_str(
let mut parser = unwrap_or_emit_fatal(new_parser_from_source_str(
psess,
FileName::cli_crate_attr_source_code(raw_attr),
raw_attr.clone(),
);
));
let start_span = parser.token.span;
let AttrItem { path, args, tokens: _ } = match parser.parse_attr_item(false) {

4
compiler/rustc_builtin_macros/src/source_util.rs
View File

@ -12,8 +12,8 @@
};
use rustc_expand::module::DirOwnership;
use rustc_lint_defs::BuiltinLintDiag;
use rustc_parse::new_parser_from_file;
use rustc_parse::parser::{ForceCollect, Parser};
use rustc_parse::{new_parser_from_file, unwrap_or_emit_fatal};
use rustc_session::lint::builtin::INCOMPLETE_INCLUDE;
use rustc_span::source_map::SourceMap;
use rustc_span::symbol::Symbol;
@ -126,7 +126,7 @@ pub(crate) fn expand_include<'cx>(
return ExpandResult::Ready(DummyResult::any(sp, guar));
}
};
let p = new_parser_from_file(cx.psess(), &file, Some(sp));
let p = unwrap_or_emit_fatal(new_parser_from_file(cx.psess(), &file, Some(sp)));
// If in the included file we have e.g., `mod bar;`,
// then the path of `bar.rs` should be relative to the directory of `file`.

6
compiler/rustc_driver_impl/src/lib.rs
View File

@ -32,7 +32,7 @@
use rustc_lint::unerased_lint_store;
use rustc_metadata::creader::MetadataLoader;
use rustc_metadata::locator;
use rustc_parse::{new_parser_from_file, new_parser_from_source_str};
use rustc_parse::{new_parser_from_file, new_parser_from_source_str, unwrap_or_emit_fatal};
use rustc_session::config::{nightly_options, CG_OPTIONS, Z_OPTIONS};
use rustc_session::config::{ErrorOutputType, Input, OutFileName, OutputType};
use rustc_session::getopts::{self, Matches};
@ -1265,12 +1265,12 @@ pub fn handle_options(early_dcx: &EarlyDiagCtxt, args: &[String]) -> Option<geto
}
fn parse_crate_attrs<'a>(sess: &'a Session) -> PResult<'a, ast::AttrVec> {
let mut parser = match &sess.io.input {
let mut parser = unwrap_or_emit_fatal(match &sess.io.input {
Input::File(file) => new_parser_from_file(&sess.psess, file, None),
Input::Str { name, input } => {
new_parser_from_source_str(&sess.psess, name.clone(), input.clone())
}
};
});
parser.parse_inner_attributes()
}

5
compiler/rustc_expand/src/module.rs
View File

@ -5,8 +5,8 @@
use rustc_ast::ptr::P;
use rustc_ast::{token, AttrVec, Attribute, Inline, Item, ModSpans};
use rustc_errors::{Diag, ErrorGuaranteed};
use rustc_parse::new_parser_from_file;
use rustc_parse::validate_attr;
use rustc_parse::{new_parser_from_file, unwrap_or_emit_fatal};
use rustc_session::parse::ParseSess;
use rustc_session::Session;
use rustc_span::symbol::{sym, Ident};
@ -66,7 +66,8 @@ pub(crate) fn parse_external_mod(
}
// Actually parse the external file as a module.
let mut parser = new_parser_from_file(&sess.psess, &mp.file_path, Some(span));
let mut parser =
unwrap_or_emit_fatal(new_parser_from_file(&sess.psess, &mp.file_path, Some(span)));
let (inner_attrs, items, inner_span) =
parser.parse_mod(&token::Eof).map_err(|err| ModError::ParserError(err))?;
attrs.extend(inner_attrs);

9
compiler/rustc_expand/src/proc_macro_server.rs
View File

@ -14,7 +14,7 @@
use rustc_errors::{Diag, ErrorGuaranteed, MultiSpan, PResult};
use rustc_parse::lexer::nfc_normalize;
use rustc_parse::parser::Parser;
use rustc_parse::source_str_to_stream;
use rustc_parse::{new_parser_from_source_str, source_str_to_stream, unwrap_or_emit_fatal};
use rustc_session::parse::ParseSess;
use rustc_span::def_id::CrateNum;
use rustc_span::symbol::{self, sym, Symbol};
@ -467,7 +467,8 @@ fn track_path(&mut self, path: &str) {
fn literal_from_str(&mut self, s: &str) -> Result<Literal<Self::Span, Self::Symbol>, ()> {
let name = FileName::proc_macro_source_code(s);
let mut parser = rustc_parse::new_parser_from_source_str(self.psess(), name, s.to_owned());
let mut parser =
unwrap_or_emit_fatal(new_parser_from_source_str(self.psess(), name, s.to_owned()));
let first_span = parser.token.span.data();
let minus_present = parser.eat(&token::BinOp(token::Minus));
@ -539,12 +540,12 @@ fn is_empty(&mut self, stream: &Self::TokenStream) -> bool {
}
fn from_str(&mut self, src: &str) -> Self::TokenStream {
source_str_to_stream(
unwrap_or_emit_fatal(source_str_to_stream(
self.psess(),
FileName::proc_macro_source_code(src),
src.to_string(),
Some(self.call_site),
)
))
}
fn to_string(&mut self, stream: &Self::TokenStream) -> String {

6
compiler/rustc_interface/src/interface.rs
View File

@ -14,7 +14,7 @@
use rustc_middle::ty;
use rustc_middle::ty::CurrentGcx;
use rustc_middle::util::Providers;
use rustc_parse::maybe_new_parser_from_source_str;
use rustc_parse::new_parser_from_source_str;
use rustc_query_impl::QueryCtxt;
use rustc_query_system::query::print_query_stack;
use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
@ -67,7 +67,7 @@ macro_rules! error {
};
}
match maybe_new_parser_from_source_str(&psess, filename, s.to_string()) {
match new_parser_from_source_str(&psess, filename, s.to_string()) {
Ok(mut parser) => match parser.parse_meta_item() {
Ok(meta_item) if parser.token == token::Eof => {
if meta_item.path.segments.len() != 1 {
@ -166,7 +166,7 @@ macro_rules! error {
error!("expected `cfg(name, values(\"value1\", \"value2\", ... \"valueN\"))`")
};
let mut parser = match maybe_new_parser_from_source_str(&psess, filename, s.to_string()) {
let mut parser = match new_parser_from_source_str(&psess, filename, s.to_string()) {
Ok(parser) => parser,
Err(errs) => {
errs.into_iter().for_each(|err| err.cancel());

8
compiler/rustc_interface/src/passes.rs
View File

@ -19,7 +19,9 @@
use rustc_middle::dep_graph::DepGraph;
use rustc_middle::ty::{self, GlobalCtxt, RegisteredTools, TyCtxt};
use rustc_middle::util::Providers;
use rustc_parse::{new_parser_from_file, new_parser_from_source_str, validate_attr};
use rustc_parse::{
new_parser_from_file, new_parser_from_source_str, unwrap_or_emit_fatal, validate_attr,
};
use rustc_passes::{abi_test, hir_stats, layout_test};
use rustc_resolve::Resolver;
use rustc_session::code_stats::VTableSizeInfo;
@ -43,12 +45,12 @@
pub fn parse<'a>(sess: &'a Session) -> PResult<'a, ast::Crate> {
let krate = sess.time("parse_crate", || {
let mut parser = match &sess.io.input {
let mut parser = unwrap_or_emit_fatal(match &sess.io.input {
Input::File(file) => new_parser_from_file(&sess.psess, file, None),
Input::Str { input, name } => {
new_parser_from_source_str(&sess.psess, name.clone(), input.clone())
}
};
});
parser.parse_crate_mod()
})?;

54
compiler/rustc_parse/src/lib.rs
View File

@ -35,7 +35,7 @@
rustc_fluent_macro::fluent_messages! { "../messages.ftl" }
// Unwrap the result if `Ok`, otherwise emit the diagnostics and abort.
fn unwrap_or_emit_fatal<T>(expr: Result<T, Vec<Diag<'_>>>) -> T {
pub fn unwrap_or_emit_fatal<T>(expr: Result<T, Vec<Diag<'_>>>) -> T {
match expr {
Ok(expr) => expr,
Err(errs) => {
@ -47,25 +47,28 @@ fn unwrap_or_emit_fatal<T>(expr: Result<T, Vec<Diag<'_>>>) -> T {
}
}
/// Creates a new parser from a source string.
pub fn new_parser_from_source_str(psess: &ParseSess, name: FileName, source: String) -> Parser<'_> {
unwrap_or_emit_fatal(maybe_new_parser_from_source_str(psess, name, source))
}
/// Creates a new parser from a source string. Returns any buffered errors from lexing the initial
/// 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(
/// Creates a new parser from a source string. On failure, the errors must be consumed via
/// `unwrap_or_emit_fatal`, `emit`, `cancel`, etc., otherwise a panic will occur when they are
/// dropped.
pub fn new_parser_from_source_str(
psess: &ParseSess,
name: FileName,
source: String,
) -> Result<Parser<'_>, Vec<Diag<'_>>> {
maybe_new_parser_from_source_file(psess, psess.source_map().new_source_file(name, source))
let source_file = psess.source_map().new_source_file(name, source);
new_parser_from_source_file(psess, source_file)
}
/// Creates a new parser, aborting if the file doesn't exist. If a span is given, that is used on
/// an error as the source of the problem.
pub fn new_parser_from_file<'a>(psess: &'a ParseSess, path: &Path, sp: Option<Span>) -> Parser<'a> {
/// Creates a new parser from a filename. On failure, the errors must be consumed via
/// `unwrap_or_emit_fatal`, `emit`, `cancel`, etc., otherwise a panic will occur when they are
/// dropped.
///
/// If a span is given, that is used on an error as the source of the problem.
pub fn new_parser_from_file<'a>(
psess: &'a ParseSess,
path: &Path,
sp: Option<Span>,
) -> Result<Parser<'a>, Vec<Diag<'a>>> {
let source_file = psess.source_map().load_file(path).unwrap_or_else(|e| {
let msg = format!("couldn't read {}: {}", path.display(), e);
let mut err = psess.dcx.struct_fatal(msg);
@ -74,23 +77,21 @@ pub fn new_parser_from_file<'a>(psess: &'a ParseSess, path: &Path, sp: Option<Sp
}
err.emit();
});
unwrap_or_emit_fatal(maybe_new_parser_from_source_file(psess, source_file))
new_parser_from_source_file(psess, source_file)
}
/// Given a session and a `source_file`, return a parser. Returns any buffered errors from lexing
/// the initial token stream.
fn maybe_new_parser_from_source_file(
fn new_parser_from_source_file(
psess: &ParseSess,
source_file: Lrc<SourceFile>,
) -> Result<Parser<'_>, Vec<Diag<'_>>> {
let end_pos = source_file.end_position();
let stream = maybe_source_file_to_stream(psess, source_file, None)?;
let stream = source_file_to_stream(psess, source_file, None)?;
let mut parser = Parser::new(psess, stream, None);
if parser.token == token::Eof {
parser.token.span = Span::new(end_pos, end_pos, parser.token.span.ctxt(), None);
}
Ok(parser)
}
@ -99,14 +100,14 @@ pub fn source_str_to_stream(
name: FileName,
source: String,
override_span: Option<Span>,
) -> TokenStream {
) -> Result<TokenStream, Vec<Diag<'_>>> {
let source_file = psess.source_map().new_source_file(name, source);
unwrap_or_emit_fatal(maybe_source_file_to_stream(psess, source_file, override_span))
source_file_to_stream(psess, 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_source_file_to_stream<'psess>(
fn source_file_to_stream<'psess>(
psess: &'psess ParseSess,
source_file: Lrc<SourceFile>,
override_span: Option<Span>,
@ -139,13 +140,18 @@ pub fn parse_in<'a, T>(
pub fn fake_token_stream_for_item(psess: &ParseSess, item: &ast::Item) -> TokenStream {
let source = pprust::item_to_string(item);
let filename = FileName::macro_expansion_source_code(&source);
source_str_to_stream(psess, filename, source, Some(item.span))
unwrap_or_emit_fatal(source_str_to_stream(psess, filename, source, Some(item.span)))
}
pub fn fake_token_stream_for_crate(psess: &ParseSess, krate: &ast::Crate) -> TokenStream {
let source = pprust::crate_to_string_for_macros(krate);
let filename = FileName::macro_expansion_source_code(&source);
source_str_to_stream(psess, filename, source, Some(krate.spans.inner_span))
unwrap_or_emit_fatal(source_str_to_stream(
psess,
filename,
source,
Some(krate.spans.inner_span),
))
}
pub fn parse_cfg_attr(

22
compiler/rustc_parse/src/parser/tests.rs
View File

@ -1,5 +1,7 @@
use crate::parser::ForceCollect;
use crate::{new_parser_from_source_str, parser::Parser, source_str_to_stream};
use crate::{
new_parser_from_source_str, parser::Parser, source_str_to_stream, unwrap_or_emit_fatal,
};
use ast::token::IdentIsRaw;
use rustc_ast::ptr::P;
use rustc_ast::token::{self, Delimiter, Token};
@ -29,7 +31,11 @@ fn psess() -> ParseSess {
/// Map string to parser (via tts).
fn string_to_parser(psess: &ParseSess, source_str: String) -> Parser<'_> {
new_parser_from_source_str(psess, PathBuf::from("bogofile").into(), source_str)
unwrap_or_emit_fatal(new_parser_from_source_str(
psess,
PathBuf::from("bogofile").into(),
source_str,
))
}
fn create_test_handler() -> (DiagCtxt, Lrc<SourceMap>, Arc<Mutex<Vec<u8>>>) {
@ -82,7 +88,12 @@ fn with_expected_parse_error<T, F>(source_str: &str, expected_output: &str, f: F
/// Maps a string to tts, using a made-up filename.
pub(crate) fn string_to_stream(source_str: String) -> TokenStream {
let psess = psess();
source_str_to_stream(&psess, PathBuf::from("bogofile").into(), source_str, None)
unwrap_or_emit_fatal(source_str_to_stream(
&psess,
PathBuf::from("bogofile").into(),
source_str,
None,
))
}
/// Parses a string, returns a crate.
@ -1064,7 +1075,8 @@ fn parse_item_from_source_str(
source: String,
psess: &ParseSess,
) -> PResult<'_, Option<P<ast::Item>>> {
new_parser_from_source_str(psess, name, source).parse_item(ForceCollect::No)
unwrap_or_emit_fatal(new_parser_from_source_str(psess, name, source))
.parse_item(ForceCollect::No)
}
// Produces a `rustc_span::span`.
@ -1345,7 +1357,7 @@ fn parse_expr_from_source_str(
source: String,
psess: &ParseSess,
) -> PResult<'_, P<ast::Expr>> {
new_parser_from_source_str(psess, name, source).parse_expr()
unwrap_or_emit_fatal(new_parser_from_source_str(psess, name, source)).parse_expr()
}
create_default_session_globals_then(|| {

2
src/librustdoc/clean/render_macro_matchers.rs
View File

@ -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());

23
src/librustdoc/doctest.rs
View File

@ -9,7 +9,7 @@
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();

11
src/librustdoc/passes/lint/check_code_block_syntax.rs
View File

@ -5,7 +5,7 @@
translation::{to_fluent_args, Translate},
Applicability, DiagCtxt, DiagInner, LazyFallbackBundle,
};
use rustc_parse::source_str_to_stream;
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};
@ -51,8 +51,13 @@ 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(|| {
source_str_to_stream(&psess, FileName::Custom(String::from("doctest")), source, Some(span))
.is_empty()
unwrap_or_emit_fatal(source_str_to_stream(
&psess,
FileName::Custom(String::from("doctest")),
source,
Some(span),
))
.is_empty()
})
.unwrap_or(false);
let buffer = buffer.borrow();

4
src/tools/clippy/clippy_lints/src/doc/needless_doctest_main.rs
View File

@ -8,7 +8,7 @@
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 @@ fn check_code_sample(code: String, edition: Edition, ignore: bool) -> (bool, Vec
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);

10
src/tools/rustfmt/src/parse/parser.rs
View File

@ -4,7 +4,8 @@
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, unwrap_or_emit_fatal};
use rustc_span::{sym, Span};
use thin_vec::ThinVec;
@ -68,10 +69,10 @@ fn parser(
) -> Result<rustc_parse::parser::Parser<'a>, Option<Vec<Diag<'a>>>> {
match input {
Input::File(ref file) => catch_unwind(AssertUnwindSafe(move || {
new_parser_from_file(psess, file, None)
unwrap_or_emit_fatal(new_parser_from_file(psess, file, None))
}))
.map_err(|_| None),
Input::Text(text) => rustc_parse::maybe_new_parser_from_source_str(
Input::Text(text) => rustc_parse::new_parser_from_source_str(
psess,
rustc_span::FileName::Custom("stdin".to_owned()),
text,
@ -111,7 +112,8 @@ pub(crate) fn parse_file_as_module(
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) => {

4
tests/ui-fulldeps/mod_dir_path_canonicalized.rs
View File

@ -16,7 +16,7 @@
#[allow(unused_extern_crates)]
extern crate rustc_driver;
use rustc_parse::new_parser_from_file;
use rustc_parse::{new_parser_from_file, unwrap_or_emit_fatal};
use rustc_session::parse::ParseSess;
use std::path::Path;
@ -34,6 +34,6 @@ fn parse() {
let path = Path::new(file!());
let path = path.canonicalize().unwrap();
let mut parser = new_parser_from_file(&psess, &path, None);
let mut parser = unwrap_or_emit_fatal(new_parser_from_file(&psess, &path, None));
let _ = parser.parse_crate_mod();
}

7
tests/ui-fulldeps/pprust-expr-roundtrip.rs
View File

@ -36,7 +36,7 @@
use rustc_ast::ptr::P;
use rustc_ast::*;
use rustc_ast_pretty::pprust;
use rustc_parse::new_parser_from_source_str;
use rustc_parse::{new_parser_from_source_str, unwrap_or_emit_fatal};
use rustc_session::parse::ParseSess;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::Ident;
@ -46,8 +46,9 @@
fn parse_expr(psess: &ParseSess, src: &str) -> Option<P<Expr>> {
let src_as_string = src.to_string();
let mut p =
new_parser_from_source_str(psess, FileName::Custom(src_as_string.clone()), src_as_string);
let mut p = unwrap_or_emit_fatal(
new_parser_from_source_str(psess, FileName::Custom(src_as_string.clone()), src_as_string)
);
p.parse_expr().map_err(|e| e.cancel()).ok()
}