Remove -Zshow-span.

It's very old (added in #12087). It's strange, and it's not clear what
its use cases are. It only works with the crate root file because it
runs before expansion. I suspect it won't be missed.

Author: nnethercote

Diff for: compiler/rustc_ast_passes/messages.ftl

@@ -207,8 +207,6 @@ ast_passes_precise_capturing_duplicated = duplicate `use<...>` precise capturing
 
 ast_passes_precise_capturing_not_allowed_here = `use<...>` precise capturing syntax not allowed in {$loc}
 
-ast_passes_show_span = {$msg}
-
 ast_passes_stability_outside_std = stability attributes may not be used outside of the standard library
 
 ast_passes_static_without_body =

Diff for: compiler/rustc_ast_passes/src/errors.rs

@@ -779,14 +779,6 @@ pub(crate) struct IncompatibleFeatures {
     pub f2: Symbol,
 }
 
-#[derive(Diagnostic)]
-#[diag(ast_passes_show_span)]
-pub(crate) struct ShowSpan {
-    #[primary_span]
-    pub span: Span,
-    pub msg: &'static str,
-}
-
 #[derive(Diagnostic)]
 #[diag(ast_passes_negative_bound_not_supported)]
 pub(crate) struct NegativeBoundUnsupported {

Diff for: compiler/rustc_ast_passes/src/lib.rs

@@ -1,8 +1,6 @@
 //! The `rustc_ast_passes` crate contains passes which validate the AST in `syntax`
 //! parsed by `rustc_parse` and then lowered, after the passes in this crate,
 //! by `rustc_ast_lowering`.
-//!
-//! The crate also contains other misc AST visitors, e.g. `node_count` and `show_span`.
 
 // tidy-alphabetical-start
 #![allow(internal_features)]
@@ -18,6 +16,5 @@
 pub mod ast_validation;
 mod errors;
 pub mod feature_gate;
-pub mod show_span;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }

Diff for: compiler/rustc_ast_passes/src/show_span.rs

@@ -418,9 +418,7 @@ fn run_compiler(
                 return early_exit();
             }
 
-            if sess.opts.unstable_opts.parse_crate_root_only
-                || sess.opts.unstable_opts.show_span.is_some()
-            {
+            if sess.opts.unstable_opts.parse_crate_root_only {
                 return early_exit();
             }
 

Diff for: compiler/rustc_driver_impl/src/lib.rs

@@ -54,10 +54,6 @@ pub(crate) fn parse<'a>(sess: &'a Session) -> Result<ast::Crate> {
         })
         .map_err(|parse_error| parse_error.emit())?;
 
-    if let Some(ref s) = sess.opts.unstable_opts.show_span {
-        rustc_ast_passes::show_span::run(sess.dcx(), s, &krate);
-    }
-
     if sess.opts.unstable_opts.input_stats {
         input_stats::print_ast_stats(&krate, "PRE EXPANSION AST STATS", "ast-stats-1");
     }

Diff for: compiler/rustc_interface/src/passes.rs

@@ -843,7 +843,6 @@ fn test_unstable_options_tracking_hash() {
     tracked!(sanitizer_recover, SanitizerSet::ADDRESS);
     tracked!(saturating_float_casts, Some(true));
     tracked!(share_generics, Some(true));
-    tracked!(show_span, Some(String::from("abc")));
     tracked!(simulate_remapped_rust_src_base, Some(PathBuf::from("/rustc/abc")));
     tracked!(small_data_threshold, Some(16));
     tracked!(split_lto_unit, Some(true));

Diff for: compiler/rustc_interface/src/tests.rs

@@ -2036,8 +2036,6 @@ written to standard error output)"),
         "make the current crate share its generic instantiations"),
     shell_argfiles: bool = (false, parse_bool, [UNTRACKED],
         "allow argument files to be specified with POSIX \"shell-style\" argument quoting"),
-    show_span: Option<String> = (None, parse_opt_string, [TRACKED],
-        "show spans in the crate root file, for compiler debugging (expr|pat|ty)"),
     simulate_remapped_rust_src_base: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
         "simulate the effect of remap-debuginfo = true at bootstrapping by remapping path \
         to rust's source base directory. only meant for testing purposes"),