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.)

2 files changed, 8 insertions, 6 deletions

diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index 5254a6576f9..c95a10f4e8d 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -14,7 +14,7 @@ use rustc_lint::LintStore;
 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 @@ pub(crate) fn parse_cfg(dcx: &DiagCtxt, cfgs: Vec<String>) -> Cfg {
                 };
             }
 
-            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 @@ pub(crate) fn parse_check_cfg(dcx: &DiagCtxt, specs: Vec<String>) -> CheckCfg {
             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());
diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index b3ed6622097..a342577cffb 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -19,7 +19,9 @@ use rustc_middle::arena::Arena;
 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 @@ use tracing::{info, instrument};
 
 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()
     })?;