From c602cec7887470db3e8ed69600f5bd2f38e160d5 Mon Sep 17 00:00:00 2001
From: Googler <steinman@google.com>
Date: Fri, 10 Mar 2023 14:38:08 -0800
Subject: [PATCH] Allow --extra_execution_platforms to support overrides by
 making it no longer "allowMultiple".

RELNOTES:
Subsequent settings of --extra_execution_platforms now override previous settings, instead of adding them to a list. If you currently set --extra_execution_platforms more than once, please migrate by passing a list of values to --extra_execution_platforms instead so that earlier values aren't overwritten.

current
--extra_execution_platforms=platform1
--extra_execution_platforms=platform2

future
--extra_execution_platforms=platform1,platform2
PiperOrigin-RevId: 515741836
Change-Id: I435f6a18482b1890d401ef31d5c4c94fde7e9ff3
---
 site/en/docs/user-manual.md                                 | 2 ++
 .../google/devtools/build/lib/analysis/PlatformOptions.java | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/site/en/docs/user-manual.md b/site/en/docs/user-manual.md
index 7a567bc2f31f41..75aa2d974f8d99 100644
--- a/site/en/docs/user-manual.md
+++ b/site/en/docs/user-manual.md
@@ -1326,6 +1326,8 @@ The platforms that are available as execution platforms to run actions.
 Platforms can be specified by exact target, or as a target pattern. These
 platforms will be considered before those declared in the WORKSPACE file by
 [register_execution_platforms()](/rules/lib/globals#register_execution_platforms).
+This option accepts a comma-separated list of platforms in order of priority.
+If the flag is passed multiple times, the most recent overrides.
 
 #### `--extra_toolchains={{ "<var>" }}labels{{ "</var>" }}` {:#extra-toolchains}
 
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
index a217fc85bf4bf3..6d1c021fa8e15c 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
@@ -76,15 +76,15 @@ public static boolean platformIsDefault(Label platform) {
   @Option(
       name = "extra_execution_platforms",
       converter = CommaSeparatedOptionListConverter.class,
-      defaultValue = "null",
+      defaultValue = "",
       documentationCategory = OptionDocumentationCategory.TOOLCHAIN,
-      allowMultiple = true,
       effectTags = {OptionEffectTag.EXECUTION},
       help =
           "The platforms that are available as execution platforms to run actions. "
               + "Platforms can be specified by exact target, or as a target pattern. "
               + "These platforms will be considered before those declared in the WORKSPACE file by "
-              + "register_execution_platforms().")
+              + "register_execution_platforms(). This option may only be set once; later "
+              + "instances will override earlier flag settings.")
   public List<String> extraExecutionPlatforms;
 
   @Option(