Add --host_action_env option

This PR adds `--host_action_env` option to specify a set of environment variables to be added to the host configuration. The variables specified by this option are only added to host configuration while those specified by `--action_env` are only included in the target configuration.

Fixes: #4008

Closes #12122.

PiperOrigin-RevId: 333060884

src/main/java/com/google/devtools/build/lib/analysis/config/CoreOptions.java

@@ -342,14 +342,30 @@ public String getTypeDescription() {
       documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
       effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
       help =
-          "Specifies the set of environment variables available to actions. "
-              + "Variables can be either specified by name, in which case the value will be "
-              + "taken from the invocation environment, or by the name=value pair which sets "
-              + "the value independent of the invocation environment. This option can be used "
-              + "multiple times; for options given for the same variable, the latest wins, options "
-              + "for different variables accumulate.")
+          "Specifies the set of environment variables available to actions with target"
+              + " configuration. Variables can be either specified by name, in which case the"
+              + " value will be taken from the invocation environment, or by the name=value pair"
+              + " which sets the value independent of the invocation environment. This option can"
+              + " be used multiple times; for options given for the same variable, the latest"
+              + " wins, options for different variables accumulate.")
   public List<Map.Entry<String, String>> actionEnvironment;
 
+  @Option(
+      name = "host_action_env",
+      converter = Converters.OptionalAssignmentConverter.class,
+      allowMultiple = true,
+      defaultValue = "null",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {OptionEffectTag.ACTION_COMMAND_LINES},
+      help =
+          "Specifies the set of environment variables available to actions with host or execution"
+              + " configurations. Variables can be either specified by name, in which case the"
+              + " value will be taken from the invocation environment, or by the name=value pair"
+              + " which sets the value independent of the invocation environment. This option can"
+              + " be used multiple times; for options given for the same variable, the latest"
+              + " wins, options for different variables accumulate.")
+  public List<Map.Entry<String, String>> hostActionEnvironment;
+
   @Option(
       name = "repo_env",
       converter = Converters.OptionalAssignmentConverter.class,
@@ -957,6 +973,9 @@ public FragmentOptions getHost() {
     host.hostCpu = hostCpu;
     host.hostCompilationMode = hostCompilationMode;
 
+    // Pass host action environment variables
+    host.actionEnvironment = hostActionEnvironment;
+
     return host;
   }