rustc: add --print target-spec option

This option provides the user the ability to dump the configuration that
is in use by rustc for the target they are building for.

Signed-off-by: Doug Goldstein <[email protected]>

Author: cardoe

src/librustc/session/config.rs

@@ -164,6 +164,7 @@ pub enum PrintRequest {
     CrateName,
     Cfg,
     TargetList,
+    TargetSpec,
 }
 
 pub enum Input {
@@ -905,7 +906,7 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
                  "[asm|llvm-bc|llvm-ir|obj|link|dep-info]"),
         opt::multi_s("", "print", "Comma separated list of compiler information to \
                                print on stdout",
-                 "[crate-name|file-names|sysroot|cfg|target-list]"),
+                 "[crate-name|file-names|sysroot|cfg|target-list|target-spec]"),
         opt::flagmulti_s("g",  "",  "Equivalent to -C debuginfo=2"),
         opt::flagmulti_s("O", "", "Equivalent to -C opt-level=2"),
         opt::opt_s("o", "", "Write output to <filename>", "FILENAME"),
@@ -1189,6 +1190,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
             "sysroot" => PrintRequest::Sysroot,
             "cfg" => PrintRequest::Cfg,
             "target-list" => PrintRequest::TargetList,
+            "target-spec" => PrintRequest::TargetSpec,
             req => {
                 early_error(error_format, &format!("unknown print request `{}`", req))
             }

src/librustc_driver/lib.rs

@@ -76,6 +76,8 @@ use rustc_metadata::loader;
 use rustc_metadata::cstore::CStore;
 use rustc::util::common::time;
 
+use serialize::json::ToJson;
+
 use std::cmp::max;
 use std::cmp::Ordering::Equal;
 use std::default::Default;
@@ -560,6 +562,7 @@ impl RustcDefaultCalls {
                     println!("{}", targets.join("\n"));
                 },
                 PrintRequest::Sysroot => println!("{}", sess.sysroot().display()),
+                PrintRequest::TargetSpec => println!("{}", sess.target.target.to_json().pretty()),
                 PrintRequest::FileNames |
                 PrintRequest::CrateName => {
                     let input = match input {