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

RELNOTES: None.
PiperOrigin-RevId: 177337384

2 files changed, 21 insertions, 4 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.
diff --git a/src/test/java/com/google/devtools/build/lib/rules/apple/XcodeConfigTest.java b/src/test/java/com/google/devtools/build/lib/rules/apple/XcodeConfigTest.java
index 93c1dabfc5..e2c21f7658 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/apple/XcodeConfigTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/apple/XcodeConfigTest.java
@@ -286,7 +286,7 @@ public class XcodeConfigTest extends BuildViewTestCase {
         "xcode_config(",
         "    name = 'foo',",
         "    require_defined_version = 1,",
-        "    versions = [':version512'],",
+        "    versions = [':version512', ':version84'],",
         "    default = ':version512',",
         ")",
         "",
@@ -294,11 +294,16 @@ public class XcodeConfigTest extends BuildViewTestCase {
         "    name = 'version512',",
         "    version = '5.1.2',",
         "    aliases = ['5', '5.1'],",
+        ")",
+        "xcode_version(",
+        "    name = 'version84',",
+        "    version = '8.4',",
         ")");
     useConfiguration("--xcode_version=6");
     reporter.removeHandler(failFastHandler);
     getConfiguredTarget("//xcode:foo");
-    assertContainsEvent("6 matches no alias in the config");
+    assertContainsEvent("--xcode_version=6 specified, but '6' is not an available Xcode version. "
+        + "available versions: [5.1.2, 8.4]");
   }
 
   @Test