Flip the --incompatible_depset_is_not_iterable flag

RELNOTES[INC]: Depsets can't be iterated over unless they're converted to lists
using the .to_list() method. Use --incompatible_depset_is_not_iterable=false to
temporarily restore the previous behaviour.

#5816

PiperOrigin-RevId: 251249558

Author: vladmos

site/docs/skylark/backward-compatibility.md

@@ -108,7 +108,7 @@ sorted(deps.to_list())  # recommended
 ```
 
 *   Flag: `--incompatible_depset_is_not_iterable`
-*   Default: `false`
+*   Default: `true`
 *   Tracking issue: [#5816](https://github.com/bazelbuild/bazel/issues/5816)
 
 

src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java

@@ -190,7 +190,7 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
 
   @Option(
       name = "incompatible_depset_is_not_iterable",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
       metadataTags = {

src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java

@@ -228,7 +228,7 @@ public static Builder builderWithDefaults() {
           .experimentalStarlarkConfigTransitions(true)
           .experimentalStarlarkUnusedInputsList(false)
           .incompatibleBzlDisallowLoadAfterStatement(true)
-          .incompatibleDepsetIsNotIterable(false)
+          .incompatibleDepsetIsNotIterable(true)
           .incompatibleDepsetUnion(true)
           .incompatibleDisableThirdPartyLicenseChecking(true)
           .incompatibleDisableDeprecatedAttrParams(true)