From: Takuro Ashie <ashie>
Date: Thu, 18 Apr 2019 07:21:00 -0700
Subject: Bug 1545437 - Add options to specify Rust target name

Certain build systems such as Yocto know more suitable Rust target name, so it
would be better that there is a way to pass it to Mozilla's build system.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1545437
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=954774
Forwarded: https://phabricator.services.mozilla.com/D28069
Applied-upstream: no, upstream consider this a workaround and do not support armel
---
 build/moz.configure/rust.configure | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/build/moz.configure/rust.configure b/build/moz.configure/rust.configure
index 9647cbc..5aed73f 100644
--- a/build/moz.configure/rust.configure
+++ b/build/moz.configure/rust.configure
@@ -218,6 +218,28 @@ def rust_supported_targets(rustc):
     return namespace(per_os=per_os, per_raw_os=per_raw_os)
 
 
+option(env='RUST_HOST',
+       nargs=1,
+       help='Define the system type for Rust performing the build')
+
+@depends('RUST_HOST')
+@checking('rust host', lambda host: host)
+def rust_host_env(value):
+    if value:
+        return value[0]
+
+
+option(env='RUST_TARGET',
+       nargs=1,
+       help='Define the system type for Rust where the resulting executables will be used')
+
+@depends('RUST_TARGET')
+@checking('rust target', lambda target: target)
+def rust_target_env(value):
+    if value:
+        return value[0]
+
+
 @template
 def rust_triple_alias(host_or_target):
     """Template defining the alias used for rustc's --target flag.
@@ -228,8 +250,9 @@ def rust_triple_alias(host_or_target):
 
     host_or_target_str = {host: 'host', target: 'target'}[host_or_target]
 
-    @depends(rustc, host_or_target, c_compiler, rust_supported_targets,
-             arm_target, when=rust_compiler)
+    @depends(rustc, host_or_target, rust_host_env, rust_target_env,
+             c_compiler, rust_supported_targets, arm_target,
+             when=rust_compiler)
     @checking('for rust %s triplet' % host_or_target_str)
     @imports('os')
     @imports('subprocess')
@@ -237,8 +260,14 @@ def rust_triple_alias(host_or_target):
     @imports(_from='mozbuild.shellutil', _import='quote')
     @imports(_from='tempfile', _import='mkstemp')
     @imports(_from='textwrap', _import='dedent')
-    def rust_target(rustc, host_or_target, compiler_info,
-                    rust_supported_targets, arm_target):
+    def rust_target(rustc, host_or_target, rust_host_env, rust_target_env,
+                    compiler_info, rust_supported_targets, arm_target):
+
+        specified_targets = {"host": rust_host_env, "target": rust_target_env}
+        specified_target = specified_targets[host_or_target_str]
+        if (specified_target):
+            return specified_target
+
         # Rust's --target options are similar to, but not exactly the same
         # as, the autoconf-derived targets we use.  An example would be that
         # Rust uses distinct target triples for targetting the GNU C++ ABI