feat: add support for computed values via skipped questions (#1220)

* feat: add support for computed values via skipped questions

* docs: apply review suggestions

Co-authored-by: Jairo Llopis <[email protected]>

* docs: update inline comments

* docs: fix formatting

---------

Co-authored-by: Jairo Llopis <[email protected]>

copier/main.py

@@ -257,6 +257,7 @@ def _answers_to_remember(self) -> Mapping:
             (str(k), v)
             for (k, v) in self.answers.combined.items()
             if not k.startswith("_")
+            and k not in self.answers.hidden
             and k not in self.template.secret_questions
             and k in self.template.questions_data
             and isinstance(k, JSONSerializable)
@@ -413,7 +414,6 @@ def _render_allowed(
     def _ask(self) -> None:
         """Ask the questions of the questionary and record their answers."""
         result = AnswersMap(
-            default=self.template.default_answers,
             user_defaults=self.user_defaults,
             init=self.data,
             last=self.subproject.last_answers,
@@ -427,12 +427,14 @@ def _ask(self) -> None:
                 var_name=var_name,
                 **details,
             )
-            # Skip a question when the skip condition is met and remove any data
-            # from the answers map, so no answer for this question is recorded
-            # in the answers file.
+            # Skip a question when the skip condition is met.
             if not question.get_when():
-                result.remove(var_name)
-                continue
+                # Omit its answer from the answers file.
+                result.hide(var_name)
+                # Skip immediately to the next question when it has no default
+                # value.
+                if question.default is MISSING:
+                    continue
             if var_name in result.init:
                 # Try to parse the answer value.
                 answer = question.parse_answer(result.init[var_name])
@@ -452,7 +454,8 @@ def _ask(self) -> None:
                         raise ValueError(f'Question "{var_name}" is required')
                 else:
                     new_answer = unsafe_prompt(
-                        [question.get_questionary_structure()], answers=result.combined
+                        [question.get_questionary_structure()],
+                        answers={question.var_name: question.get_default()},
                     )[question.var_name]
             except KeyboardInterrupt as err:
                 raise CopierAnswersInterrupt(result, question, self.template) from err

copier/template.py

@@ -281,11 +281,6 @@ def config_data(self) -> AnyByStrDict:
             verify_copier_version(result["min_copier_version"])
         return result
 
-    @cached_property
-    def default_answers(self) -> AnyByStrDict:
-        """Get default answers for template's questions."""
-        return {key: value.get("default") for key, value in self.questions_data.items()}
-
     @cached_property
     def envops(self) -> Mapping:
         """Get the Jinja configuration specified in the template, or default values.

copier/user_data.py

@@ -103,54 +103,43 @@ class AnswersMap:
         last:
             Data from [the answers file][the-copier-answersyml-file].
 
-        default:
-            Default data from the template.
-
-            See [copier.template.Template.default_answers][].
-
         user_defaults:
             Default data from the user e.g. previously completed and restored data.
 
             See [copier.main.Worker][].
     """
 
     # Private
-    removed: Set[str] = field(default_factory=set, init=False)
+    hidden: Set[str] = field(default_factory=set, init=False)
 
     # Public
     user: AnyByStrDict = field(default_factory=dict)
     init: AnyByStrDict = field(default_factory=dict)
     metadata: AnyByStrDict = field(default_factory=dict)
     last: AnyByStrDict = field(default_factory=dict)
     user_defaults: AnyByStrDict = field(default_factory=dict)
-    default: AnyByStrDict = field(default_factory=dict)
 
     @property
     def combined(self) -> Mapping[str, Any]:
         """Answers combined from different sources, sorted by priority."""
-        combined = dict(
+        return dict(
             ChainMap(
                 self.user,
                 self.init,
                 self.metadata,
                 self.last,
                 self.user_defaults,
-                self.default,
                 DEFAULT_DATA,
             )
         )
-        for key in self.removed:
-            if key in combined:
-                del combined[key]
-        return combined
 
     def old_commit(self) -> OptStr:
         """Commit when the project was updated from this template the last time."""
         return self.last.get("_commit")
 
-    def remove(self, key: str) -> None:
+    def hide(self, key: str) -> None:
         """Remove an answer by key."""
-        self.removed.add(key)
+        self.hidden.add(key)
 
 
 @dataclass(config=AllowArbitraryTypes)

docs/configuring.md

@@ -175,17 +175,14 @@ Supported keys:
 
 -   **when**: Condition that, if `false`, skips the question.
 
-    If it is a boolean, it is used directly, but it's a bit absurd in that case.
+    If it is a boolean, it is used directly. Setting it to `false` is useful for
+    creating a computed value.
 
     If it is a string, it is converted to boolean using a parser similar to YAML, but
-    only for boolean values.
+    only for boolean values. The string can be [templated][prompt-templating].
 
-    This is most useful when [templated](#prompt-templating).
-
-    If a question is skipped, its answer will be:
-
-    -   The default value, if you're generating the project for the 1st time.
-    -   The last answer recorded, if you're updating the project.
+    If a question is skipped, its answer is not recorded, but its default value is
+    available in the render context.
 
     !!! example
 

tests/test_complex_questions.py

@@ -397,6 +397,7 @@ def test_tui_inherited_default(
                 "{{ _copier_answers|to_nice_yaml }}"
             ),
             (src / "answers.json.jinja"): "{{ _copier_answers|to_nice_json }}",
+            (src / "context.json.jinja"): '{"owner2": "{{ owner2 }}"}',
         }
     )
     with local.cwd(src):
@@ -423,6 +424,7 @@ def test_tui_inherited_default(
         **({"owner2": owner2} if has_2_owners else {}),
     }
     assert json.loads((dst / "answers.json").read_text()) == result
+    assert json.loads((dst / "context.json").read_text()) == {"owner2": owner2}
     with local.cwd(dst):
         git("init")
         git("add", "--all")
@@ -432,6 +434,45 @@ def test_tui_inherited_default(
     assert json.loads((dst / "answers.json").read_text()) == result
 
 
+def test_tui_typed_default(
+    tmp_path_factory: pytest.TempPathFactory, spawn: Spawn
+) -> None:
+    """Make sure a template defaults are typed as expected."""
+    src, dst = map(tmp_path_factory.mktemp, ("src", "dst"))
+    build_file_tree(
+        {
+            (src / "copier.yaml"): (
+                """\
+                test1:
+                    type: bool
+                    default: false
+                    when: false
+                test2:
+                    type: bool
+                    default: "{{ 'a' == 'b' }}"
+                    when: false
+                """
+            ),
+            (src / "{{ _copier_conf.answers_file }}.jinja"): (
+                "{{ _copier_answers|to_nice_yaml }}"
+            ),
+            (src / "answers.json.jinja"): "{{ _copier_answers|to_nice_json }}",
+            (src / "context.json.jinja"): (
+                """\
+                {"test1": "{{ test1 }}", "test2": "{{ test2 }}"}
+                """
+            ),
+        }
+    )
+    tui = spawn(COPIER_PATH + ("copy", str(src), str(dst)), timeout=10)
+    tui.expect_exact(pexpect.EOF)
+    assert json.loads((dst / "answers.json").read_text()) == {"_src_path": str(src)}
+    assert json.loads((dst / "context.json").read_text()) == {
+        "test1": "False",
+        "test2": "False",
+    }
+
+
 def test_selection_type_cast(
     tmp_path_factory: pytest.TempPathFactory, spawn: Spawn
 ) -> None:
@@ -559,8 +600,16 @@ def test_omit_answer_for_skipped_question(
             (src / "{{ _copier_conf.answers_file }}.jinja"): (
                 "{{ _copier_answers|to_nice_yaml }}"
             ),
+            (src / "context.yml.jinja"): yaml.safe_dump(
+                {
+                    "disabled": "{{ disabled }}",
+                    "disabled_with_default": "{{ disabled_with_default }}",
+                }
+            ),
         }
     )
     run_copy(str(src), dst, defaults=True, data={"disabled": "hello"})
     answers = yaml.safe_load((dst / ".copier-answers.yml").read_text())
     assert answers == {"_src_path": str(src)}
+    context = yaml.safe_load((dst / "context.yml").read_text())
+    assert context == {"disabled": "hello", "disabled_with_default": "hello"}

tests/test_prompt.py

@@ -183,6 +183,11 @@ def test_when(
             (src / "[[ _copier_conf.answers_file ]].tmpl"): (
                 "[[ _copier_answers|to_nice_yaml ]]"
             ),
+            (src / "context.yml.tmpl"): (
+                """\
+                question_2: [[ question_2 ]]
+                """
+            ),
         }
     )
     tui = spawn(COPIER_PATH + ("copy", str(src), str(dst)), timeout=10)
@@ -198,6 +203,8 @@ def test_when(
         "question_1": question_1,
         **({"question_2": "something"} if asks else {}),
     }
+    context = yaml.safe_load((dst / "context.yml").read_text())
+    assert context == {"question_2": "something"}
 
 
 def test_placeholder(tmp_path_factory: pytest.TempPathFactory, spawn: Spawn) -> None: