Make top-level `rustc_parse` functions fallible.

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.)

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_builtin_macros/src/source_util.rs b/compiler/rustc_builtin_macros/src/source_util.rs
index 29e991525a9..dc1d82df0c3 100644
--- a/compiler/rustc_builtin_macros/src/source_util.rs
+++ b/compiler/rustc_builtin_macros/src/source_util.rs
@@ -12,8 +12,8 @@ use rustc_expand::base::{
 };
 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`.