Improve error messaging for invalid values of the --xcode_version flag.

RELNOTES: None.
PiperOrigin-RevId: 177337384

1 files changed, 14 insertions, 2 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
index 1b6e998d3c..abb00c0a21 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
@@ -14,11 +14,14 @@
 
 package com.google.devtools.build.lib.rules.apple;
 
+import static java.util.stream.Collectors.joining;
+
 import com.google.common.base.Joiner;
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Maps;
+import com.google.common.collect.Streams;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetFactory;
@@ -173,14 +176,23 @@ public class XcodeConfig implements RuleConfiguredTargetFactory {
       if (explicitVersion != null) {
         return explicitVersion;
       } else {
-        throw new XcodeConfigException(
-            String.format("%s matches no alias in the config", versionOverrideFlag));
+        throw new XcodeConfigException(String.format(
+            "--xcode_version=%s specified, but '%s' is not an available Xcode version. "
+            + "available versions: [%s]",
+            versionOverrideFlag, versionOverrideFlag,
+            printableXcodeVersions(xcodeVersionRules)));
       }
     }
 
     return defaultVersion;
   }
 
+  private static String printableXcodeVersions(Iterable<XcodeVersionRuleData> xcodeVersions) {
+    return Streams.stream(xcodeVersions)
+        .map(versionData -> versionData.getVersion().toString())
+        .collect(joining(", "));
+  }
+
   /**
    * Returns a map where keys are "names" of xcode versions as defined by the configuration target,
    * and values are the rule data objects which contain information regarding that xcode version.