Delay parsing of --cfg and --check-cfg options.

By storing the unparsed values in `Config` and then parsing them within
`run_compiler`, the parsing functions can use the main symbol interner,
and not create their own short-lived interners.

This change also eliminates the need for one `EarlyErrorHandler` in
rustdoc, because parsing errors can be reported by another, slightly
later `EarlyErrorHandler`.

compiler/rustc_driver_impl/src/lib.rs

@@ -317,13 +317,11 @@ fn run_compiler(
         return Ok(());
     }
 
-    let cfg = interface::parse_cfg(&early_error_handler, matches.opt_strs("cfg"));
-    let check_cfg = interface::parse_check_cfg(&early_error_handler, matches.opt_strs("check-cfg"));
     let (odir, ofile) = make_output(&matches);
     let mut config = interface::Config {
         opts: sopts,
-        crate_cfg: cfg,
-        crate_check_cfg: check_cfg,
+        crate_cfg: matches.opt_strs("cfg"),
+        crate_check_cfg: matches.opt_strs("check-cfg"),
         input: Input::File(PathBuf::new()),
         output_file: ofile,
         output_dir: odir,

compiler/rustc_interface/src/interface.rs

@@ -65,10 +65,6 @@ impl Compiler {
 
 /// Converts strings provided as `--cfg [cfgspec]` into a `Cfg`.
 pub fn parse_cfg(handler: &EarlyErrorHandler, cfgs: Vec<String>) -> Cfg<String> {
-    // This creates a short-lived `SessionGlobals`, containing an interner. The
-    // parsed values are converted from symbols to strings before exiting
-    // because the symbols are meaningless once the interner is gone.
-    rustc_span::create_default_session_if_not_set_then(move |_| {
     cfgs.into_iter()
         .map(|s| {
             let sess = ParseSess::with_silent_emitter(Some(format!(
@@ -123,14 +119,10 @@ pub fn parse_cfg(handler: &EarlyErrorHandler, cfgs: Vec<String>) -> Cfg<String>
             }
         })
         .collect::<Cfg<String>>()
-    })
 }
 
 /// Converts strings provided as `--check-cfg [specs]` into a `CheckCfg`.
 pub fn parse_check_cfg(handler: &EarlyErrorHandler, specs: Vec<String>) -> CheckCfg<String> {
-    // The comment about `SessionGlobals` and symbols in `parse_cfg` above
-    // applies here too.
-    rustc_span::create_default_session_if_not_set_then(move |_| {
     // If any --check-cfg is passed then exhaustive_values and exhaustive_names
     // are enabled by default.
     let exhaustive_names = !specs.is_empty();
@@ -353,17 +345,16 @@ pub fn parse_check_cfg(handler: &EarlyErrorHandler, specs: Vec<String>) -> Check
     }
 
     check_cfg
-    })
 }
 
 /// The compiler configuration
 pub struct Config {
     /// Command line options
     pub opts: config::Options,
 
-    /// cfg! configuration in addition to the default ones
-    pub crate_cfg: Cfg<String>,
-    pub crate_check_cfg: CheckCfg<String>,
+    /// Unparsed cfg! configuration in addition to the default ones.
+    pub crate_cfg: Vec<String>,
+    pub crate_check_cfg: Vec<String>,
 
     pub input: Input,
     pub output_dir: Option<PathBuf>,
@@ -436,8 +427,8 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
             let (mut sess, codegen_backend) = util::create_session(
                 &handler,
                 config.opts,
-                config.crate_cfg,
-                config.crate_check_cfg,
+                parse_cfg(&handler, config.crate_cfg),
+                parse_check_cfg(&handler, config.crate_check_cfg),
                 config.locale_resources,
                 config.file_loader,
                 CompilerIO {

src/librustdoc/core.rs

@@ -14,8 +14,8 @@ use rustc_lint::{late_lint_mod, MissingDoc};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
 use rustc_session::config::{self, CrateType, ErrorOutputType, ResolveDocLinks};
+use rustc_session::lint;
 use rustc_session::Session;
-use rustc_session::{lint, EarlyErrorHandler};
 use rustc_span::symbol::sym;
 use rustc_span::{source_map, Span};
 
@@ -175,7 +175,6 @@ pub(crate) fn new_handler(
 
 /// Parse, resolve, and typecheck the given crate.
 pub(crate) fn create_config(
-    handler: &EarlyErrorHandler,
     RustdocOptions {
         input,
         crate_name,
@@ -255,8 +254,8 @@ pub(crate) fn create_config(
 
     interface::Config {
         opts: sessopts,
-        crate_cfg: interface::parse_cfg(handler, cfgs),
-        crate_check_cfg: interface::parse_check_cfg(handler, check_cfgs),
+        crate_cfg: cfgs,
+        crate_check_cfg: check_cfgs,
         input,
         output_file: None,
         output_dir: None,

src/librustdoc/doctest.rs

@@ -13,7 +13,7 @@ use rustc_parse::parser::attr::InnerAttrPolicy;
 use rustc_resolve::rustdoc::span_of_fragments;
 use rustc_session::config::{self, CrateType, ErrorOutputType};
 use rustc_session::parse::ParseSess;
-use rustc_session::{lint, EarlyErrorHandler, Session};
+use rustc_session::{lint, Session};
 use rustc_span::edition::Edition;
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::sym;
@@ -85,18 +85,13 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
         ..config::Options::default()
     };
 
-    let early_error_handler = EarlyErrorHandler::new(ErrorOutputType::default());
-
     let mut cfgs = options.cfgs.clone();
     cfgs.push("doc".to_owned());
     cfgs.push("doctest".to_owned());
     let config = interface::Config {
         opts: sessopts,
-        crate_cfg: interface::parse_cfg(&early_error_handler, cfgs),
-        crate_check_cfg: interface::parse_check_cfg(
-            &early_error_handler,
-            options.check_cfgs.clone(),
-        ),
+        crate_cfg: cfgs,
+        crate_check_cfg: options.check_cfgs.clone(),
         input,
         output_file: None,
         output_dir: None,

src/librustdoc/lib.rs

@@ -757,8 +757,7 @@ fn main_args(
         (false, true) => {
             let input = options.input.clone();
             let edition = options.edition;
-            let config =
-                core::create_config(handler, options, &render_options, using_internal_features);
+            let config = core::create_config(options, &render_options, using_internal_features);
 
             // `markdown::render` can invoke `doctest::make_test`, which
             // requires session globals and a thread pool, so we use
@@ -791,7 +790,7 @@ fn main_args(
     let scrape_examples_options = options.scrape_examples_options.clone();
     let bin_crate = options.bin_crate;
 
-    let config = core::create_config(handler, options, &render_options, using_internal_features);
+    let config = core::create_config(options, &render_options, using_internal_features);
 
     interface::run_compiler(config, |compiler| {
         let sess = compiler.session();