Support target-spec json file extension in various cases (case-insensitive)

Author: boozook

compiler/rustc_session/src/config.rs

@@ -1991,7 +1991,7 @@ fn collect_print_requests(
 
 pub fn parse_target_triple(early_dcx: &EarlyDiagCtxt, matches: &getopts::Matches) -> TargetTriple {
     match matches.opt_str("target") {
-        Some(target) if target.ends_with(".json") => {
+        Some(target) if TargetTriple::has_json_ext(&target) => {
             let path = Path::new(&target);
             TargetTriple::from_path(path).unwrap_or_else(|_| {
                 early_dcx.early_fatal(format!("target file {path:?} does not exist"))

compiler/rustc_target/src/spec/mod.rs

@@ -3709,6 +3709,18 @@ impl TargetTriple {
             }
         }
     }
+
+    /// Helper function to check if the given `triple` ends with `".json"` __case-insensitive__.
+    /// Does not check if the path exists.
+    pub fn has_json_ext<S: AsRef<str>>(triple: S) -> bool {
+        const EXT: &'static str = ".json";
+        triple.as_ref().ends_with(EXT) || {
+            let s = triple.as_ref();
+            s.get(s.len().wrapping_sub(EXT.len())..)
+                .map(|ext| ext.eq_ignore_ascii_case(EXT))
+                .unwrap_or_default()
+        }
+    }
 }
 
 impl fmt::Display for TargetTriple {