Detect panic strategy using rustc --print cfg

Instead of relying on a command line parameter, detect if a target
is able to unwind or not.
Ignore tests that require unwinding on targets that don't support it.

src/tools/compiletest/src/common.rs

@@ -278,10 +278,6 @@ pub struct Config {
     /// override this setting.
     pub optimize_tests: bool,
 
-    /// What panic strategy the target is built with.  Unwind supports Abort, but
-    /// not vice versa.
-    pub target_panic: PanicStrategy,
-
     /// Target system to be tested
     pub target: String,
 
@@ -426,6 +422,10 @@ impl Config {
         *&self.target_cfg().pointer_width
     }
 
+    pub fn can_unwind(&self) -> bool {
+        self.target_cfg().panic == PanicStrategy::Unwind
+    }
+
     pub fn has_asm_support(&self) -> bool {
         static ASM_SUPPORTED_ARCHS: &[&str] = &[
             "x86", "x86_64", "arm", "aarch64", "riscv32",
@@ -446,6 +446,7 @@ pub struct TargetCfg {
     families: Vec<String>,
     pointer_width: u32,
     endian: Endian,
+    panic: PanicStrategy,
 }
 
 #[derive(Eq, PartialEq, Clone, Debug)]
@@ -481,6 +482,7 @@ impl TargetCfg {
         let mut families = Vec::new();
         let mut pointer_width = None;
         let mut endian = None;
+        let mut panic = None;
         for line in print_cfg.lines() {
             if let Some((name, value)) = line.split_once('=') {
                 let value = value.trim_matches('"');
@@ -498,6 +500,13 @@ impl TargetCfg {
                             s => panic!("unexpected {s}"),
                         })
                     }
+                    "panic" => {
+                        panic = match value {
+                            "abort" => Some(PanicStrategy::Abort),
+                            "unwind" => Some(PanicStrategy::Unwind),
+                            s => panic!("unexpected {s}"),
+                        }
+                    }
                     _ => {}
                 }
             }
@@ -510,6 +519,7 @@ impl TargetCfg {
             families,
             pointer_width: pointer_width.unwrap(),
             endian: endian.unwrap(),
+            panic: panic.unwrap(),
         }
     }
 }

src/tools/compiletest/src/header.rs

@@ -7,7 +7,7 @@ use std::path::{Path, PathBuf};
 
 use tracing::*;
 
-use crate::common::{CompareMode, Config, Debugger, FailMode, Mode, PanicStrategy, PassMode};
+use crate::common::{CompareMode, Config, Debugger, FailMode, Mode, PassMode};
 use crate::util;
 use crate::{extract_cdb_version, extract_gdb_version};
 
@@ -949,8 +949,7 @@ pub fn make_test_description<R: Read>(
         ignore |= !has_memtag && config.parse_name_directive(ln, "needs-sanitizer-memtag");
         ignore |= !has_shadow_call_stack
             && config.parse_name_directive(ln, "needs-sanitizer-shadow-call-stack");
-        ignore |= config.target_panic == PanicStrategy::Abort
-            && config.parse_name_directive(ln, "needs-unwind");
+        ignore |= !config.can_unwind() && config.parse_name_directive(ln, "needs-unwind");
         ignore |= config.target == "wasm32-unknown-unknown"
             && config.parse_name_directive(ln, directives::CHECK_RUN_RESULTS);
         ignore |= config.debugger == Some(Debugger::Cdb) && ignore_cdb(config, ln);

src/tools/compiletest/src/main.rs

@@ -5,9 +5,7 @@
 
 extern crate test;
 
-use crate::common::{
-    expected_output_path, output_base_dir, output_relative_path, PanicStrategy, UI_EXTENSIONS,
-};
+use crate::common::{expected_output_path, output_base_dir, output_relative_path, UI_EXTENSIONS};
 use crate::common::{CompareMode, Config, Debugger, Mode, PassMode, TestPaths};
 use crate::util::logv;
 use getopts::Options;
@@ -105,7 +103,6 @@ pub fn parse_config(args: Vec<String>) -> Config {
         .optmulti("", "host-rustcflags", "flags to pass to rustc for host", "FLAGS")
         .optmulti("", "target-rustcflags", "flags to pass to rustc for target", "FLAGS")
         .optflag("", "optimize-tests", "run tests with optimizations enabled")
-        .optopt("", "target-panic", "what panic strategy the target supports", "unwind | abort")
         .optflag("", "verbose", "run tests verbosely, showing all output")
         .optflag(
             "",
@@ -258,11 +255,6 @@ pub fn parse_config(args: Vec<String>) -> Config {
         host_rustcflags: Some(matches.opt_strs("host-rustcflags").join(" ")),
         target_rustcflags: Some(matches.opt_strs("target-rustcflags").join(" ")),
         optimize_tests: matches.opt_present("optimize-tests"),
-        target_panic: match matches.opt_str("target-panic").as_deref() {
-            Some("unwind") | None => PanicStrategy::Unwind,
-            Some("abort") => PanicStrategy::Abort,
-            _ => panic!("unknown `--target-panic` option `{}` given", mode),
-        },
         target,
         host: opt_str2(matches.opt_str("host")),
         cdb,