Flip --incompatible_disallow_unverified_http_downloads to default to …

…true

As discussed in #8607, downloading files over plain http without reasonable
verification afterwards (e.g., checking the sha256 sum) is a security risk
and therefore should be discouraged. Flip the the corresponding flag disallowing
such downloads to true. The flag was available with default false already in 0.29,
and migration was possible even before that, simply by adding known-good checksums.

Change-Id: Ia3d46115996bf7b7c4aed56dcd15fa7317b5d4fa
PiperOrigin-RevId: 261662705

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

@@ -455,7 +455,7 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
 
   @Option(
       name = "incompatible_disallow_unverified_http_downloads",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
       metadataTags = {

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

@@ -278,7 +278,7 @@ public static Builder builderWithDefaults() {
           .incompatibleDisallowOldStyleArgsAdd(true)
           .incompatibleDisallowRuleExecutionPlatformConstraintsAllowed(false)
           .incompatibleDisallowStructProviderSyntax(false)
-          .incompatibleDisallowUnverifiedHttpDownloads(false)
+          .incompatibleDisallowUnverifiedHttpDownloads(true)
           .incompatibleExpandDirectories(true)
           .incompatibleNewActionsApi(true)
           .incompatibleNoAttrLicense(true)