Extract print request stability gating and unknown print request help into helpers

To avoid duplicating stability check logic and make the print request
collection logic more straightforward.

Author: jieyouxu

compiler/rustc_session/src/config.rs

@@ -2032,49 +2032,13 @@ fn collect_print_requests(
     prints.extend(matches.opt_strs("print").into_iter().map(|req| {
         let (req, out) = split_out_file_name(&req);
 
-        let kind = match PRINT_KINDS.iter().find(|&&(name, _)| name == req) {
-            Some((_, PrintKind::TargetSpec)) => {
-                if unstable_opts.unstable_options {
-                    PrintKind::TargetSpec
-                } else {
-                    early_dcx.early_fatal(
-                        "the `-Z unstable-options` flag must also be passed to \
-                         enable the target-spec-json print option",
-                    );
-                }
-            }
-            Some((_, PrintKind::AllTargetSpecs)) => {
-                if unstable_opts.unstable_options {
-                    PrintKind::AllTargetSpecs
-                } else {
-                    early_dcx.early_fatal(
-                        "the `-Z unstable-options` flag must also be passed to \
-                         enable the all-target-specs-json print option",
-                    );
-                }
-            }
-            Some((_, PrintKind::CheckCfg)) => {
-                if unstable_opts.unstable_options {
-                    PrintKind::CheckCfg
-                } else {
-                    early_dcx.early_fatal(
-                        "the `-Z unstable-options` flag must also be passed to \
-                         enable the check-cfg print option",
-                    );
-                }
-            }
-            Some(&(_, print_kind)) => print_kind,
-            None => {
-                let prints =
-                    PRINT_KINDS.iter().map(|(name, _)| format!("`{name}`")).collect::<Vec<_>>();
-                let prints = prints.join(", ");
-
-                let mut diag =
-                    early_dcx.early_struct_fatal(format!("unknown print request: `{req}`"));
-                #[allow(rustc::diagnostic_outside_of_impl)]
-                diag.help(format!("valid print requests are: {prints}"));
-                diag.emit()
-            }
+        let kind = if let Some((print_name, print_kind)) =
+            PRINT_KINDS.iter().find(|&&(name, _)| name == req)
+        {
+            check_print_request_stability(early_dcx, unstable_opts, (print_name, *print_kind));
+            *print_kind
+        } else {
+            emit_unknown_print_request_help(early_dcx, req)
         };
 
         let out = out.unwrap_or(OutFileName::Stdout);
@@ -2093,6 +2057,34 @@ fn collect_print_requests(
     prints
 }
 
+fn check_print_request_stability(
+    early_dcx: &EarlyDiagCtxt,
+    unstable_opts: &UnstableOptions,
+    (print_name, print_kind): (&str, PrintKind),
+) {
+    match print_kind {
+        PrintKind::AllTargetSpecs | PrintKind::CheckCfg | PrintKind::TargetSpec
+            if !unstable_opts.unstable_options =>
+        {
+            early_dcx.early_fatal(format!(
+                "the `-Z unstable-options` flag must also be passed to enable the `{print_name}` \
+                print option"
+            ));
+        }
+        _ => {}
+    }
+}
+
+fn emit_unknown_print_request_help(early_dcx: &EarlyDiagCtxt, req: &str) -> ! {
+    let prints = PRINT_KINDS.iter().map(|(name, _)| format!("`{name}`")).collect::<Vec<_>>();
+    let prints = prints.join(", ");
+
+    let mut diag = early_dcx.early_struct_fatal(format!("unknown print request: `{req}`"));
+    #[allow(rustc::diagnostic_outside_of_impl)]
+    diag.help(format!("valid print requests are: {prints}"));
+    diag.emit()
+}
+
 pub fn parse_target_triple(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> TargetTuple {
     match matches.opt_str("target") {
         Some(target) if target.ends_with(".json") => {