parsing: Support dict unpacking in cmd.

Allow to use dictionaries as values for template interpolation but only inside the `cmd` key.

See tests/func/parsing/test_interpolated_entry.py::test_cmd_dict for detailed syntax.

Add `config.parsing` section for configuring behavior of ambiguous data types
like booleans and lists.

dvc/config_schema.py

@@ -282,4 +282,8 @@ SCHEMA = {
         "plots": str,
         "live": str,
     },
+    "parsing": {
+        "bool": All(Lower, Choices("store_true", "boolean_optional")),
+        "list": All(Lower, Choices("nargs", "append")),
+    },
 }

dvc/parsing/__init__.py

@@ -303,7 +303,7 @@ class EntryDefinition:
     ) -> DictStr:
         try:
             return context.resolve(
-                value, skip_interpolation_checks=skip_checks
+                value, skip_interpolation_checks=skip_checks, key=key
             )
         except (ParseError, KeyNotInContext) as exc:
             format_and_raise(

dvc/parsing/context.py

@@ -18,6 +18,7 @@ from dvc.parsing.interpolate import (
     normalize_key,
     recurse,
     str_interpolate,
+    validate_value,
 )
 
 logger = logging.getLogger(__name__)
@@ -506,7 +507,7 @@ class Context(CtxDict):
                 self.data.pop(key, None)
 
     def resolve(
-        self, src, unwrap=True, skip_interpolation_checks=False
+        self, src, unwrap=True, skip_interpolation_checks=False, key=None
     ) -> Any:
         """Recursively resolves interpolation and returns resolved data.
 
@@ -522,10 +523,10 @@ class Context(CtxDict):
         {'lst': [1, 2, 3]}
         """
         func = recurse(self.resolve_str)
-        return func(src, unwrap, skip_interpolation_checks)
+        return func(src, unwrap, skip_interpolation_checks, key)
 
     def resolve_str(
-        self, src: str, unwrap=True, skip_interpolation_checks=False
+        self, src: str, unwrap=True, skip_interpolation_checks=False, key=None
     ) -> str:
         """Resolves interpolated string to it's original value,
         or in case of multiple interpolations, a combined string.
@@ -543,10 +544,12 @@ class Context(CtxDict):
             expr = get_expression(
                 matches[0], skip_checks=skip_interpolation_checks
             )
-            return self.select(expr, unwrap=unwrap)
+            value = self.select(expr, unwrap=unwrap)
+            validate_value(value, key)
+            return value
         # but not "${num} days"
         return str_interpolate(
-            src, matches, self, skip_checks=skip_interpolation_checks
+            src, matches, self, skip_checks=skip_interpolation_checks, key=key
         )
 
 

dvc/parsing/interpolate.py

@@ -1,11 +1,12 @@
 import re
 import typing
-from collections.abc import Mapping
+from collections.abc import Iterable, Mapping
 from functools import singledispatch
 
 from funcy import memoize, rpartial
 
 from dvc.exceptions import DvcException
+from dvc.utils.flatten import flatten
 
 if typing.TYPE_CHECKING:
     from typing import List, Match
@@ -80,6 +81,45 @@ def _(obj: bool):
     return "true" if obj else "false"
 
 
+@to_str.register(dict)
+def _(obj: dict):
+    from dvc.config import Config
+
+    config = Config().get("parsing", {})
+
+    result = ""
+    for k, v in flatten(obj).items():
+
+        if isinstance(v, bool):
+            if v:
+                result += f"--{k} "
+            else:
+                if config.get("bool", "store_true") == "boolean_optional":
+                    result += f"--no-{k} "
+
+        elif isinstance(v, str):
+            result += f"--{k} '{v}' "
+
+        elif isinstance(v, Iterable):
+            for n, i in enumerate(v):
+                if isinstance(i, str):
+                    i = f"'{i}'"
+                elif isinstance(i, Iterable):
+                    raise ParseError(
+                        f"Cannot interpolate nested iterable in '{k}'"
+                    )
+
+                if config.get("list", "nargs") == "append":
+                    result += f"--{k} {i} "
+                else:
+                    result += f"{i} " if n > 0 else f"--{k} {i} "
+
+        else:
+            result += f"--{k} {v} "
+
+    return result.rstrip()
+
+
 def _format_exc_msg(exc: "ParseException"):
     from pyparsing import ParseException
 
@@ -148,23 +188,33 @@ def get_expression(match: "Match", skip_checks: bool = False):
     return inner if skip_checks else parse_expr(inner)
 
 
+def validate_value(value, key):
+    from .context import PRIMITIVES
+
+    not_primitive = value is not None and not isinstance(value, PRIMITIVES)
+    not_foreach = key is not None and "foreach" not in key
+    if not_primitive and not_foreach:
+        if isinstance(value, dict):
+            if key == "cmd":
+                return True
+        raise ParseError(
+            f"Cannot interpolate data of type '{type(value).__name__}'"
+        )
+
+
 def str_interpolate(
     template: str,
     matches: "List[Match]",
     context: "Context",
     skip_checks: bool = False,
+    key=None,
 ):
-    from .context import PRIMITIVES
-
     index, buf = 0, ""
     for match in matches:
         start, end = match.span(0)
         expr = get_expression(match, skip_checks=skip_checks)
         value = context.select(expr, unwrap=True)
-        if value is not None and not isinstance(value, PRIMITIVES):
-            raise ParseError(
-                f"Cannot interpolate data of type '{type(value).__name__}'"
-            )
+        validate_value(value, key)
         buf += template[index:start] + to_str(value)
         index = end
     buf += template[index:]

tests/func/parsing/test_errors.py

@@ -119,16 +119,32 @@ def test_wdir_failed_to_interpolate(tmp_dir, dvc, wdir, expected_msg):
 
 def test_interpolate_non_string(tmp_dir, dvc):
     definition = make_entry_definition(
-        tmp_dir, "build", {"cmd": "echo ${models}"}, Context(models={})
+        tmp_dir, "build", {"outs": "${models}"}, Context(models={})
+    )
+    with pytest.raises(ResolveError) as exc_info:
+        definition.resolve()
+
+    assert str(exc_info.value) == (
+        "failed to parse 'stages.build.outs' in 'dvc.yaml':\n"
+        "Cannot interpolate data of type 'dict'"
+    )
+    assert definition.context == {"models": {}}
+
+
+def test_interpolate_nested_iterable(tmp_dir, dvc):
+    definition = make_entry_definition(
+        tmp_dir,
+        "build",
+        {"cmd": "echo ${models}"},
+        Context(models={"list": [1, [2, 3]]}),
     )
     with pytest.raises(ResolveError) as exc_info:
         definition.resolve()
 
     assert str(exc_info.value) == (
         "failed to parse 'stages.build.cmd' in 'dvc.yaml':\n"
-        "Cannot interpolate data of type 'dict'"
+        "Cannot interpolate nested iterable in 'list'"
     )
-    assert definition.context == {"models": {}}
 
 
 def test_partial_vars_doesnot_exist(tmp_dir, dvc):

tests/func/parsing/test_interpolated_entry.py

@@ -259,3 +259,59 @@ def test_vars_load_partial(tmp_dir, dvc, local, vars_):
         d["vars"] = vars_
     resolver = DataResolver(dvc, tmp_dir.fs_path, d)
     resolver.resolve()
+
+
+@pytest.mark.parametrize(
+    "bool_config, list_config",
+    [(None, None), ("store_true", "nargs"), ("boolean_optional", "append")],
+)
+def test_cmd_dict(tmp_dir, dvc, bool_config, list_config):
+    with dvc.config.edit() as conf:
+        if bool_config:
+            conf["parsing"]["bool"] = bool_config
+        if list_config:
+            conf["parsing"]["list"] = list_config
+
+    data = {
+        "dict": {
+            "foo": "foo",
+            "bar": 2,
+            "string": "spaced string",
+            "bool": True,
+            "bool-false": False,
+            "list": [1, 2, "foo"],
+            "nested": {"foo": "foo"},
+        }
+    }
+    (tmp_dir / DEFAULT_PARAMS_FILE).dump(data)
+    resolver = DataResolver(
+        dvc,
+        tmp_dir.fs_path,
+        {"stages": {"stage1": {"cmd": "python script.py ${dict}"}}},
+    )
+
+    if bool_config is None or bool_config == "store_true":
+        bool_resolved = " --bool"
+    else:
+        bool_resolved = " --bool --no-bool-false"
+
+    if list_config is None or list_config == "nargs":
+        list_resolved = " --list 1 2 'foo'"
+    else:
+        list_resolved = " --list 1 --list 2 --list 'foo'"
+
+    assert_stage_equal(
+        resolver.resolve(),
+        {
+            "stages": {
+                "stage1": {
+                    "cmd": "python script.py"
+                    " --foo 'foo' --bar 2"
+                    " --string 'spaced string'"
+                    f"{bool_resolved}"
+                    f"{list_resolved}"
+                    " --nested.foo 'foo'"
+                }
+            }
+        },
+    )