diff --git a/site/docs/skylark/backward-compatibility.md b/site/docs/skylark/backward-compatibility.md
index 37cad78..536b4e0 100644
--- a/site/docs/skylark/backward-compatibility.md
+++ b/site/docs/skylark/backward-compatibility.md
@@ -42,6 +42,7 @@
 *   [New args API](#new-args-api)
 *   [Disable objc provider resources](#disable-objc-provider-resources)
 *   [Disable output group field on Target](#disable-output-group-field-on-target)
+*   [Disable default parameter of output attributes](#disable-default-parameter-of-output-attributes)
 *   [Remove native git repository](#remove-native-git-repository)
 *   [Remove native http archive](#remove-native-http-archive)
 *   [New-style JavaInfo constructor](#new-style-java_info)
@@ -277,6 +278,48 @@
 *   Default: `false`
 
 
+### Disable default parameter of output attributes
+
+This flag disables the `default` parameter on `attr.output` and
+`attr.output_list`. Use Starlark macros to specify defaults for these attributes
+instead.
+
+For example, replace:
+
+```python
+my_rule = rule(
+    ...
+    attrs = { "out" : attr.output(default = "foo.txt") }
+    ...
+```
+
+with:
+
+```python
+# myrule.bzl
+my_rule = rule(
+    ...
+    attrs = { "out" : attr.output() }
+    ...
+
+# mymacro.bzl
+load(":myrule.bzl", _my_rule=”my_rule”)
+
+def my_rule(name):
+    _my_rule(
+        name = name,
+        output = "%s_out.txt" % name
+    )
+```
+
+The previous `default` parameter of these attribute types was severely
+bug-prone, as two targets of the same rule would be unable to exist in the same
+package under default behavior. (Two targets both generating `foo.txt` in the
+same package would conflict.)
+
+*   Flag: `--incompatible_no_output_attr_default`
+*   Default: `false`
+
 ### Remove native git repository
 
 When set, the native `git_repository` and `new_git_repository` rules are
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkAttr.java b/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkAttr.java
index 13cce13..51019a7 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkAttr.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkAttr.java
@@ -683,6 +683,13 @@
       Object defaultO, String doc, Boolean mandatory, FuncallExpression ast, Environment env)
       throws EvalException {
     SkylarkUtils.checkLoadingOrWorkspacePhase(env, "attr.output", ast.getLocation());
+
+    if (env.getSemantics().incompatibleNoOutputAttrDefault() && defaultO != Runtime.NONE) {
+      throw new EvalException(ast.getLocation(),
+          "'default' is no longer a supported parameter for attr.output. Use Starlark macros "
+              + "to set the default of output or output_list parameters instead. You can use "
+              + "--incompatible_no_output_attr_default=false to temporarily disable this check.");
+    }
     return createNonconfigurableAttrDescriptor(
         "output",
         EvalUtils.<String, Object>optionMap(env, DEFAULT_ARG, defaultO, MANDATORY_ARG, mandatory),
@@ -694,7 +701,7 @@
   @Override
   public Descriptor outputListAttribute(
       Boolean allowEmpty,
-      SkylarkList defaultList,
+      Object defaultList,
       String doc,
       Boolean mandatory,
       Boolean nonEmpty,
@@ -702,6 +709,14 @@
       Environment env)
       throws EvalException {
     SkylarkUtils.checkLoadingOrWorkspacePhase(env, "attr.output_list", ast.getLocation());
+
+    if (env.getSemantics().incompatibleNoOutputAttrDefault() && defaultList != Runtime.NONE) {
+      throw new EvalException(ast.getLocation(),
+          "'default' is no longer a supported parameter for attr.output_list. Use Starlark macros "
+              + "to set the default of output or output_list parameters instead. You can use "
+              + "--incompatible_no_output_attr_default=false to temporarily disable this check.");
+    }
+
     return createAttrDescriptor(
         "output_list",
         EvalUtils.<String, Object>optionMap(
diff --git a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
index e253319..9c19e2b 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/SkylarkSemanticsOptions.java
@@ -326,6 +326,19 @@
   public boolean incompatibleNewActionsApi;
 
   @Option(
+      name = "incompatible_no_output_attr_default",
+      defaultValue = "false",
+      documentationCategory = OptionDocumentationCategory.SKYLARK_SEMANTICS,
+      effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
+      metadataTags = {
+          OptionMetadataTag.INCOMPATIBLE_CHANGE,
+          OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES
+      },
+      help = "If set to true, disables the `default` parameter of the `attr.output` and "
+          + "`attr.output_list` attribute definition functions.")
+  public boolean incompatibleNoOutputAttrDefault;
+
+  @Option(
       name = "incompatible_no_support_tools_in_action_inputs",
       defaultValue = "false",
       documentationCategory = OptionDocumentationCategory.SKYLARK_SEMANTICS,
@@ -501,6 +514,7 @@
         .incompatibleExpandDirectories(incompatibleExpandDirectories)
         .incompatibleGenerateJavaCommonSourceJar(incompatibleGenerateJavaCommonSourceJar)
         .incompatibleNewActionsApi(incompatibleNewActionsApi)
+        .incompatibleNoOutputAttrDefault(incompatibleNoOutputAttrDefault)
         .incompatibleNoSupportToolsInActionInputs(incompatibleNoSupportToolsInActionInputs)
         .incompatibleNoTargetOutputGroup(incompatibleNoTargetOutputGroup)
         .incompatibleNoTransitiveLoads(incompatibleNoTransitiveLoads)
diff --git a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkAttrApi.java b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkAttrApi.java
index 96e1f4e..b688d70 100644
--- a/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkAttrApi.java
+++ b/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/SkylarkAttrApi.java
@@ -756,7 +756,9 @@
             defaultValue = "None",
             named = true,
             positional = false,
-            doc = DEFAULT_DOC),
+            doc = "<b><code>default<code> is deprecated for <code>attr.output</code>. Use "
+                + "Starlark macros to set the default for <code>output<code> and "
+                + "<code>output_list</code> attributes. <p>" + DEFAULT_DOC),
         @Param(
             name = DOC_ARG,
             type = String.class,
@@ -796,10 +798,13 @@
               @ParamType(type = SkylarkList.class, generic1 = Label.class),
               @ParamType(type = UserDefinedFunction.class)
             },
-            defaultValue = "[]",
+            noneable = true,
+            defaultValue = "None",
             named = true,
             positional = false,
-            doc = DEFAULT_DOC),
+            doc = "<b><code>default<code> is deprecated for <code>attr.output_list</code>. Use "
+                + "Starlark macros to set the default for <code>output<code> and "
+                + "<code>output_list</code> attributes. <p>" + DEFAULT_DOC),
         @Param(
             name = DOC_ARG,
             type = String.class,
@@ -826,7 +831,7 @@
       useEnvironment = true)
   public Descriptor outputListAttribute(
       Boolean allowEmpty,
-      SkylarkList<?> defaultList,
+      Object defaultList,
       String doc,
       Boolean mandatory,
       Boolean nonEmpty,
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
index 9805d61..bad29a9 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemantics.java
@@ -131,6 +131,8 @@
 
   public abstract boolean incompatibleNewActionsApi();
 
+  public abstract boolean incompatibleNoOutputAttrDefault();
+
   public abstract boolean incompatibleNoSupportToolsInActionInputs();
 
   public abstract boolean incompatibleNoTargetOutputGroup();
@@ -188,6 +190,7 @@
           .incompatibleExpandDirectories(false)
           .incompatibleGenerateJavaCommonSourceJar(false)
           .incompatibleNewActionsApi(false)
+          .incompatibleNoOutputAttrDefault(false)
           .incompatibleNoSupportToolsInActionInputs(false)
           .incompatibleNoTargetOutputGroup(false)
           .incompatibleNoTransitiveLoads(false)
@@ -246,6 +249,8 @@
 
     public abstract Builder incompatibleNewActionsApi(boolean value);
 
+    public abstract Builder incompatibleNoOutputAttrDefault(boolean value);
+
     public abstract Builder incompatibleNoSupportToolsInActionInputs(boolean value);
 
     public abstract Builder incompatibleNoTargetOutputGroup(boolean value);
diff --git a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeSkylarkAttrApi.java b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeSkylarkAttrApi.java
index f0ea8a6..d72333a 100644
--- a/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeSkylarkAttrApi.java
+++ b/src/main/java/com/google/devtools/build/skydoc/fakebuildapi/FakeSkylarkAttrApi.java
@@ -91,7 +91,7 @@
   }
 
   @Override
-  public Descriptor outputListAttribute(Boolean allowEmpty, SkylarkList<?> defaultList, String doc,
+  public Descriptor outputListAttribute(Boolean allowEmpty, Object defaultList, String doc,
       Boolean mandatory, Boolean nonEmpty, FuncallExpression ast, Environment env)
       throws EvalException {
     return new FakeDescriptor(Type.OUTPUT_LIST, doc, mandatory);
diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 933ef11..3ce2097 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -141,6 +141,7 @@
         "--incompatible_expand_directories=" + rand.nextBoolean(),
         "--incompatible_generate_javacommon_source_jar=" + rand.nextBoolean(),
         "--incompatible_new_actions_api=" + rand.nextBoolean(),
+        "--incompatible_no_output_attr_default=" + rand.nextBoolean(),
         "--incompatible_no_support_tools_in_action_inputs=" + rand.nextBoolean(),
         "--incompatible_no_target_output_group=" + rand.nextBoolean(),
         "--incompatible_no_transitive_loads=" + rand.nextBoolean(),
@@ -182,6 +183,7 @@
         .incompatibleExpandDirectories(rand.nextBoolean())
         .incompatibleGenerateJavaCommonSourceJar(rand.nextBoolean())
         .incompatibleNewActionsApi(rand.nextBoolean())
+        .incompatibleNoOutputAttrDefault(rand.nextBoolean())
         .incompatibleNoSupportToolsInActionInputs(rand.nextBoolean())
         .incompatibleNoTargetOutputGroup(rand.nextBoolean())
         .incompatibleNoTransitiveLoads(rand.nextBoolean())
diff --git a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
index c8734de..9d4a1e3 100644
--- a/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skylark/SkylarkIntegrationTest.java
@@ -1053,6 +1053,90 @@
   }
 
   @Test
+  public void testNoOutputAttrDefault() throws Exception {
+    setSkylarkSemanticsOptions("--incompatible_no_output_attr_default=true");
+
+    scratch.file(
+        "test/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out_file = ctx.actions.declare_file(ctx.attr._o1.name)",
+        "  ctx.actions.write(output=out_file, content='hi')",
+        "  return struct(o1=ctx.attr._o1)",
+        "",
+        "def output_fn():",
+        "  return Label('//test/skylark:foo.txt')",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl,",
+        "  attrs = {'_o1': attr.output(default = output_fn)})");
+
+    scratch.file(
+        "test/BUILD",
+        "load('//test:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'r')");
+
+    reporter.removeHandler(failFastHandler);
+    getConfiguredTarget("//test:r");
+    assertContainsEvent("'default' is no longer a supported parameter for attr.output");
+  }
+
+  @Test
+  public void testNoOutputListAttrDefault() throws Exception {
+    setSkylarkSemanticsOptions("--incompatible_no_output_attr_default=true");
+
+    scratch.file(
+        "test/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  return []",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl,",
+        "  attrs = {'outs': attr.output_list(default = [])})");
+
+    scratch.file(
+        "test/BUILD",
+        "load('//test:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'r')");
+
+    reporter.removeHandler(failFastHandler);
+    getConfiguredTarget("//test:r");
+    assertContainsEvent("'default' is no longer a supported parameter for attr.output_list");
+  }
+
+  @Test
+  public void testLegacyOutputAttrDefault() throws Exception {
+    // Note that use of the "default" parameter of attr.output and attr.output_label is deprecated
+    // and barely functional. This test simply serves as proof-of-concept verification that the
+    // legacy behavior remains intact.
+    setSkylarkSemanticsOptions("--incompatible_no_output_attr_default=false");
+
+    scratch.file(
+        "test/skylark/extension.bzl",
+        "def custom_rule_impl(ctx):",
+        "  out_file = ctx.actions.declare_file(ctx.attr._o1.name)",
+        "  ctx.actions.write(output=out_file, content='hi')",
+        "  return struct(o1=ctx.attr._o1,",
+        "                o2=ctx.attr.o2)",
+        "",
+        "def output_fn():",
+        "  return Label('//test/skylark:foo.txt')",
+        "",
+        "custom_rule = rule(implementation = custom_rule_impl,",
+        "  attrs = {'_o1': attr.output(default = output_fn),",
+        "           'o2': attr.output_list(default = [])})");
+
+    scratch.file(
+        "test/skylark/BUILD",
+        "load('//test/skylark:extension.bzl', 'custom_rule')",
+        "",
+        "custom_rule(name = 'cr')");
+
+    ConfiguredTarget target = getConfiguredTarget("//test/skylark:cr");
+    assertThat(target.get("o1")).isEqualTo(Label.parseAbsoluteUnchecked("//test/skylark:foo.txt"));
+    assertThat(target.get("o2")).isEqualTo(MutableList.empty());
+  }
+
+  @Test
   public void testRuleClassNonMandatoryEmptyOutputs() throws Exception {
     scratch.file(
         "test/skylark/extension.bzl",