implement --print=all-target-specs-json

compiler/rustc_driver_impl/src/lib.rs

@@ -44,8 +44,10 @@ use rustc_session::{early_error, early_error_no_abort, early_warn};
 use rustc_span::source_map::{FileLoader, FileName};
 use rustc_span::symbol::sym;
 use rustc_target::json::ToJson;
+use rustc_target::spec::{Target, TargetTriple};
 
 use std::cmp::max;
+use std::collections::BTreeMap;
 use std::env;
 use std::ffi::OsString;
 use std::fs;
@@ -648,6 +650,15 @@ fn print_crate_info(
             TargetSpec => {
                 println!("{}", serde_json::to_string_pretty(&sess.target.to_json()).unwrap());
             }
+            AllTargetSpecs => {
+                let mut targets = BTreeMap::new();
+                for name in rustc_target::spec::TARGETS {
+                    let triple = TargetTriple::from_triple(name);
+                    let target = Target::expect_builtin(&triple);
+                    targets.insert(name, target.to_json());
+                }
+                println!("{}", serde_json::to_string_pretty(&targets).unwrap());
+            }
             FileNames | CrateName => {
                 let Some(attrs) = attrs.as_ref() else {
                     // no crate attributes, print out an error and exit