Support building multiple versions of a rust crate

This is only to be used in exceptional cases.
Generally we don't allow using multiple versions of a crate.

build_extra/rust/rust.gni

@@ -43,8 +43,10 @@ template("run_rustc") {
                              "cfg",
                              "crate_name",
                              "crate_type",
+                             "crate_version",
                              "deps",
                              "extern",
+                             "extern_version",
                              "features",
                              "is_test",
                              "source_root",
@@ -75,21 +77,27 @@ template("run_rustc") {
       args += [ "--color=always" ]
     }
 
+    if (!defined(crate_version)) {
+      crate_name_and_version = crate_name
+    } else {
+      crate_name_and_version = "$crate_name-$crate_version"
+    }
+
     if (crate_type == "staticlib") {
-      output_file = "$target_out_dir/$crate_name.a"
+      output_file = "$target_out_dir/$crate_name_and_version.a"
       emit_type = "link"
     } else if (crate_type == "bin") {
-      output_file = "$target_out_dir/$crate_name.o"
+      output_file = "$target_out_dir/$crate_name_and_version.o"
       emit_type = "obj"
     } else if (crate_type == "rlib") {
-      output_file = "$target_out_dir/lib$crate_name.rlib"
+      output_file = "$target_out_dir/lib$crate_name_and_version.rlib"
       emit_type = "link"
     }
     outputs += [ output_file ]
     output_file_rel = rebase_path(output_file, root_build_dir)
     args += [ "--emit=$emit_type=$output_file_rel" ]
 
-    depfile = "$target_out_dir/$crate_name.d"
+    depfile = "$target_out_dir/$crate_name_and_version.d"
     args += [
       "--emit=dep-info=" + rebase_path(depfile, root_build_dir),
 
@@ -99,6 +107,13 @@ template("run_rustc") {
       "--output_file=" + output_file_rel,
     ]
 
+    if (defined(crate_version)) {
+      args += [
+        "-C",
+        "metadata=$crate_version",
+      ]
+    }
+
     if (is_debug) {
       args += [ "-g" ]
     }
@@ -137,48 +152,77 @@ template("run_rustc") {
       deps = []
     }
 
+    # Convert all 'extern' and 'extern_version' items to a single format.
+    extern_infos = []
     if (defined(extern)) {
-      deps += extern
       foreach(label, extern) {
-        name = get_label_info(label, "name")
+        extern_infos += [
-        dir = get_label_info(label, "target_out_dir")
+          {
-        rlib = "$dir/lib$name.rlib"
+            label = label
-        args += [
+            crate_name = get_label_info(label, "name")
-          "--extern",
+            crate_name_and_version = crate_name
-          "$name=" + rebase_path(rlib, root_build_dir),
+          },
-        ]
-
-        # This is needed for transitive dependencies.
-        args += [
-          "-L",
-          "dependency=" + rebase_path(dir, root_build_dir),
         ]
       }
     }
+    if (defined(extern_version)) {
+      foreach(info, extern_version) {
+        extern_infos += [
+          {
+            forward_variables_from(info, "*")
+            crate_name_and_version = "$crate_name-$crate_version"
+          },
+        ]
+      }
+    }
+
+    # Build the list of '--extern' arguments from the 'extern_infos' array.
+    foreach(info, extern_infos) {
+      dir = get_label_info(info.label, "target_out_dir")
+      rlib = "$dir/lib${info.crate_name_and_version}.rlib"
+      args += [
+        "--extern",
+        info.crate_name + "=" + rebase_path(rlib, root_build_dir),
+
+        # This is needed for transitive dependencies.
+        "-L",
+        "dependency=" + rebase_path(dir, root_build_dir),
+      ]
+      deps += [ info.label ]
+    }
   }
 }
 
 template("rust_component") {
   rustc_name = target_name + "_rustc"
   rustc_label = ":" + rustc_name
-  crate_name = target_name
+
+  forward_variables_from(invoker,
+                         [
+                           "crate_name",
+                           "crate_type",
+                         ])
+  if (!defined(crate_name)) {
+    crate_name = target_name
+  }
+  if (!defined(crate_type)) {
+    crate_type = "rlib"
+  }
+
   run_rustc(rustc_name) {
     forward_variables_from(invoker,
                            [
                              "args",
                              "cfg",
-                             "crate_name",
+                             "crate_version",
-                             "crate_type",
                              "deps",
                              "extern",
+                             "extern_version",
                              "features",
                              "is_test",
                              "source_root",
                              "testonly",
                            ])
-    if (!defined(invoker.crate_type)) {
-      crate_type = "rlib"
-    }
   }
 
   crate_outputs = get_target_outputs(rustc_label)
@@ -208,7 +252,9 @@ template("rust_staticlib") {
                            [
                              "cfg",
                              "crate_name",
+                             "crate_version",
                              "extern",
+                             "extern_version",
                              "features",
                              "source_root",
                              "testonly",
@@ -244,6 +290,11 @@ template("rust_executable") {
     if (defined(extern)) {
       deps += extern
     }
+    if (defined(extern_version)) {
+      foreach(info, extern_version) {
+        deps += [ info.label ]
+      }
+    }
   }
 }