10 files changed, 131 insertions, 30 deletions

diff --git a/docs/markdown/snippets/devenv.md b/docs/markdown/snippets/devenv.md
index 505f971..104cfd9 100644
--- a/docs/markdown/snippets/devenv.md
+++ b/docs/markdown/snippets/devenv.md
@@ -21,3 +21,23 @@ directory, that file is loaded by gdb automatically.
 With `--dump` option, all envorinment variables that have been modified are
 printed instead of starting an interactive shell. It can be used by shell
 scripts that wish to setup their environment themself.
+
+## New `method` and `separator` kwargs on `environment()` and `meson.add_devenv()`
+
+It simplifies this common pattern:
+```meson
+env = environment()
+env.prepend('FOO', ['a', 'b'], separator: ',')
+meson.add_devenv(env)
+```
+
+becomes one line:
+```meson
+meson.add_devenv({'FOO': ['a', 'b']}, method: 'prepend', separator: ',')
+```
+
+or two lines:
+```meson
+env = environment({'FOO': ['a', 'b']}, method: 'prepend', separator: ',')
+meson.add_devenv(env)
+```
diff --git a/docs/yaml/builtins/meson.yaml b/docs/yaml/builtins/meson.yaml
index 92fc90e..09e5dbb 100644
--- a/docs/yaml/builtins/meson.yaml
+++ b/docs/yaml/builtins/meson.yaml
@@ -444,5 +444,25 @@ methods:
 
     posargs:
       env:
-        type: env
-        description: The [[@env]] object to add.
+        type: env | str | list[str] | dict[str] | dict[list[str]]
+        description: |
+          The [[@env]] object to add.
+          Since *0.62.0* list of strings is allowed in dictionnary values. In that
+          case values are joined using the separator.
+    kwargs:
+      separator:
+        type: str
+        since: 0.62.0
+        description: |
+          The separator to use for the initial values defined in
+          the first positional argument. If not explicitly specified, the default
+          path separator for the host operating system will be used, i.e. ';' for
+          Windows and ':' for UNIX/POSIX systems.
+      method:
+        type: str
+        since: 0.62.0
+        description: |
+          Must be one of 'set', 'prepend', or 'append'
+          (defaults to 'set'). Controls if initial values defined in the first
+          positional argument are prepended, appended or repace the current value
+          of the environment variable.
diff --git a/docs/yaml/functions/environment.yaml b/docs/yaml/functions/environment.yaml
index 99c8a45..5fb81e3 100644
--- a/docs/yaml/functions/environment.yaml
+++ b/docs/yaml/functions/environment.yaml
@@ -5,8 +5,29 @@ description: Returns an empty [[@env]] object.
 
 optargs:
   env:
-    type: dict[str]
+    type: str | list[str] | dict[str] | dict[list[str]]
     since: 0.52.0
     description: |
       If provided, each key/value pair is added into the [[@env]] object
       as if [[env.set]] method was called for each of them.
+      Since *0.62.0* list of strings is allowed in dictionnary values. In that
+      case values are joined using the separator.
+
+kwargs:
+  separator:
+    type: str
+    since: 0.62.0
+    description: |
+      The separator to use for the initial values defined in
+      the first positional argument. If not explicitly specified, the default
+      path separator for the host operating system will be used, i.e. ';' for
+      Windows and ':' for UNIX/POSIX systems.
+
+  method:
+    type: str
+    since: 0.62.0
+    description: |
+      Must be one of 'set', 'prepend', or 'append'
+      (defaults to 'set'). Controls if initial values defined in the first
+      positional argument are prepended, appended or repace the current value
+      of the environment variable.
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 35e5e66..6bb487b 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -46,6 +46,7 @@ from .linkers import StaticLinker
 from .interpreterbase import FeatureNew, FeatureDeprecated
 
 if T.TYPE_CHECKING:
+    from typing_extensions import Literal
     from ._typing import ImmutableListProtocol, ImmutableSetProtocol
     from .backend.backends import Backend, ExecutableSerialisation
     from .interpreter.interpreter import Test, SourceOutputs, Interpreter
@@ -451,15 +452,19 @@ class ExtractedObjects(HoldableObject):
             for source in self.get_sources(self.srclist, self.genlist)
         ]
 
+EnvInitValueType = T.Dict[str, T.Union[str, T.List[str]]]
+
 class EnvironmentVariables(HoldableObject):
-    def __init__(self, values: T.Optional[T.Dict[str, str]] = None) -> None:
+    def __init__(self, values: T.Optional[EnvValueType] = None,
+                 init_method: Literal['set', 'prepend', 'append'] = 'set', separator: str = os.pathsep) -> None:
         self.envvars: T.List[T.Tuple[T.Callable[[T.Dict[str, str], str, T.List[str], str], str], str, T.List[str], str]] = []
         # The set of all env vars we have operations for. Only used for self.has_name()
         self.varnames: T.Set[str] = set()
 
         if values:
+            init_func = getattr(self, init_method)
             for name, value in values.items():
-                self.set(name, [value])
+                init_func(name, listify(value), separator)
 
     def __repr__(self) -> str:
         repr_str = "<{0}: {1}>"
diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index 30d0e4c..380cc1d 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -63,6 +63,8 @@ from .type_checking import (
     DEPFILE_KW,
     DISABLER_KW,
     ENV_KW,
+    ENV_METHOD_KW,
+    ENV_SEPARATOR_KW,
     INSTALL_KW,
     INSTALL_MODE_KW,
     CT_INSTALL_TAG_KW,
@@ -71,6 +73,7 @@ from .type_checking import (
     REQUIRED_KW,
     NoneType,
     in_set_validator,
+    env_convertor_with_method
 )
 from . import primitives as P_OBJ
 
@@ -2610,9 +2613,9 @@ external dependencies (including libraries) must go to "dependencies".''')
         for lang in kwargs['language']:
             argsdict[lang] = argsdict.get(lang, []) + args
 
-    @noKwargs
     @noArgsFlattening
     @typed_pos_args('environment', optargs=[(str, list, dict)])
+    @typed_kwargs('environment', ENV_METHOD_KW, ENV_SEPARATOR_KW.evolve(since='0.62.0'))
     def func_environment(self, node: mparser.FunctionNode, args: T.Tuple[T.Union[None, str, T.List['TYPE_var'], T.Dict[str, 'TYPE_var']]],
                          kwargs: 'TYPE_kwargs') -> build.EnvironmentVariables:
         init = args[0]
@@ -2621,7 +2624,9 @@ external dependencies (including libraries) must go to "dependencies".''')
             msg = ENV_KW.validator(init)
             if msg:
                 raise InvalidArguments(f'"environment": {msg}')
-            return ENV_KW.convertor(init)
+            if isinstance(init, dict) and any(i for i in init.values() if isinstance(i, list)):
+                FeatureNew.single_use('List of string in dictionary value', '0.62.0', self.subproject, location=node)
+            return env_convertor_with_method(init, kwargs['method'], kwargs['separator'])
         return build.EnvironmentVariables()
 
     @typed_pos_args('join_paths', varargs=str, min_varargs=1)
diff --git a/mesonbuild/interpreter/interpreterobjects.py b/mesonbuild/interpreter/interpreterobjects.py
index 989877e..4520f09 100644
--- a/mesonbuild/interpreter/interpreterobjects.py
+++ b/mesonbuild/interpreter/interpreterobjects.py
@@ -20,7 +20,7 @@ from ..interpreterbase import (
                                typed_pos_args, typed_kwargs, typed_operator,
                                noArgsFlattening, noPosargs, noKwargs, unholder_return, TYPE_var, TYPE_kwargs, TYPE_nvar, TYPE_nkwargs,
                                flatten, resolve_second_level_holders, InterpreterException, InvalidArguments, InvalidCode)
-from ..interpreter.type_checking import NoneType
+from ..interpreter.type_checking import NoneType, ENV_SEPARATOR_KW
 from ..dependencies import Dependency, ExternalLibrary, InternalDependency
 from ..programs import ExternalProgram
 from ..mesonlib import HoldableObject, MesonException, OptionKey, listify, Popen_safe
@@ -232,10 +232,6 @@ class RunProcess(MesonInterpreterObject):
     def stderr_method(self, args: T.List[TYPE_var], kwargs: TYPE_kwargs) -> str:
         return self.stderr
 
-
-_ENV_SEPARATOR_KW = KwargInfo('separator', str, default=os.pathsep)
-
-
 class EnvironmentVariablesHolder(ObjectHolder[build.EnvironmentVariables], MutableInterpreterObject):
 
     def __init__(self, obj: build.EnvironmentVariables, interpreter: 'Interpreter'):
@@ -260,20 +256,20 @@ class EnvironmentVariablesHolder(ObjectHolder[build.EnvironmentVariables], Mutab
             FeatureNew(m, '0.58.0', location=self.current_node).use(self.subproject)
 
     @typed_pos_args('environment.set', str, varargs=str, min_varargs=1)
-    @typed_kwargs('environment.set', _ENV_SEPARATOR_KW)
+    @typed_kwargs('environment.set', ENV_SEPARATOR_KW)
     def set_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
         self.held_object.set(name, values, kwargs['separator'])
 
     @typed_pos_args('environment.append', str, varargs=str, min_varargs=1)
-    @typed_kwargs('environment.append', _ENV_SEPARATOR_KW)
+    @typed_kwargs('environment.append', ENV_SEPARATOR_KW)
     def append_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
         self.warn_if_has_name(name)
         self.held_object.append(name, values, kwargs['separator'])
 
     @typed_pos_args('environment.prepend', str, varargs=str, min_varargs=1)
-    @typed_kwargs('environment.prepend', _ENV_SEPARATOR_KW)
+    @typed_kwargs('environment.prepend', ENV_SEPARATOR_KW)
     def prepend_method(self, args: T.Tuple[str, T.List[str]], kwargs: 'EnvironmentSeparatorKW') -> None:
         name, values = args
         self.warn_if_has_name(name)
diff --git a/mesonbuild/interpreter/mesonmain.py b/mesonbuild/interpreter/mesonmain.py
index 5781e03..4533c4a 100644
--- a/mesonbuild/interpreter/mesonmain.py
+++ b/mesonbuild/interpreter/mesonmain.py
@@ -12,7 +12,7 @@ from .. import mlog
 
 from ..mesonlib import MachineChoice, OptionKey
 from ..programs import OverrideProgram, ExternalProgram
-from ..interpreter.type_checking import ENV_KW
+from ..interpreter.type_checking import ENV_KW, ENV_METHOD_KW, ENV_SEPARATOR_KW, env_convertor_with_method
 from ..interpreterbase import (MesonInterpreterObject, FeatureNew, FeatureDeprecated,
                                typed_pos_args,  noArgsFlattening, noPosargs, noKwargs,
                                typed_kwargs, KwargInfo, InterpreterException)
@@ -20,6 +20,7 @@ from .primitives import MesonVersionString
 from .type_checking import NATIVE_KW, NoneType
 
 if T.TYPE_CHECKING:
+    from typing_extensions import Literal
     from ..backend.backends import ExecutableSerialisation
     from ..compilers import Compiler
     from ..interpreterbase import TYPE_kwargs, TYPE_var
@@ -41,6 +42,10 @@ if T.TYPE_CHECKING:
 
         native: mesonlib.MachineChoice
 
+    class AddDevenvKW(TypedDict):
+        method: Literal['set', 'prepend', 'append']
+        separator: str
+
 
 class MesonMain(MesonInterpreterObject):
     def __init__(self, build: 'build.Build', interpreter: 'Interpreter'):
@@ -438,13 +443,14 @@ class MesonMain(MesonInterpreterObject):
         return prop_name in self.interpreter.environment.properties[kwargs['native']]
 
     @FeatureNew('add_devenv', '0.58.0')
-    @noKwargs
+    @typed_kwargs('environment', ENV_METHOD_KW, ENV_SEPARATOR_KW.evolve(since='0.62.0'))
     @typed_pos_args('add_devenv', (str, list, dict, build.EnvironmentVariables))
-    def add_devenv_method(self, args: T.Tuple[T.Union[str, list, dict, build.EnvironmentVariables]], kwargs: 'TYPE_kwargs') -> None:
+    def add_devenv_method(self, args: T.Tuple[T.Union[str, list, dict, build.EnvironmentVariables]],
+                          kwargs: 'AddDevenvKW') -> None:
         env = args[0]
         msg = ENV_KW.validator(env)
         if msg:
             raise build.InvalidArguments(f'"add_devenv": {msg}')
-        converted = ENV_KW.convertor(env)
+        converted = env_convertor_with_method(env, kwargs['method'], kwargs['separator'])
         assert isinstance(converted, build.EnvironmentVariables)
         self.build.devenv.append(converted)
diff --git a/mesonbuild/interpreter/type_checking.py b/mesonbuild/interpreter/type_checking.py
index e94027b..cce794f 100644
--- a/mesonbuild/interpreter/type_checking.py
+++ b/mesonbuild/interpreter/type_checking.py
@@ -3,10 +3,13 @@
 
 """Helpers for strict type checking."""
 
+from __future__ import annotations
+import os
 import typing as T
 
 from .. import compilers
-from ..build import EnvironmentVariables, CustomTarget, BuildTarget, CustomTargetIndex, ExtractedObjects, GeneratedList, IncludeDirs
+from ..build import (EnvironmentVariables, EnvInitValueType, CustomTarget, BuildTarget,
+                     CustomTargetIndex, ExtractedObjects, GeneratedList, IncludeDirs)
 from ..coredata import UserFeatureOption
 from ..interpreterbase import TYPE_var
 from ..interpreterbase.decorators import KwargInfo, ContainerTypeInfo
@@ -16,6 +19,8 @@ from ..programs import ExternalProgram
 # Helper definition for type checks that are `Optional[T]`
 NoneType: T.Type[None] = type(None)
 
+if T.TYPE_CHECKING:
+    from typing_extensions import Literal
 
 def in_set_validator(choices: T.Set[str]) -> T.Callable[[str], T.Optional[str]]:
     """Check that the choice given was one of the given set."""
@@ -131,7 +136,8 @@ REQUIRED_KW: KwargInfo[T.Union[bool, UserFeatureOption]] = KwargInfo(
 
 DISABLER_KW: KwargInfo[bool] = KwargInfo('disabler', bool, default=False)
 
-def _env_validator(value: T.Union[EnvironmentVariables, T.List['TYPE_var'], T.Dict[str, 'TYPE_var'], str, None]) -> T.Optional[str]:
+def _env_validator(value: T.Union[EnvironmentVariables, T.List['TYPE_var'], T.Dict[str, 'TYPE_var'], str, None],
+                   allow_dict_list: bool = True) -> T.Optional[str]:
     def _splitter(v: str) -> T.Optional[str]:
         split = v.split('=', 1)
         if len(split) == 1:
@@ -152,12 +158,18 @@ def _env_validator(value: T.Union[EnvironmentVariables, T.List['TYPE_var'], T.Di
     elif isinstance(value, dict):
         # We don't need to spilt here, just do the type checking
         for k, dv in value.items():
-            if not isinstance(dv, str):
+            if allow_dict_list:
+                if any(i for i in listify(dv) if not isinstance(i, str)):
+                    return f"Dictionary element {k} must be a string or list of strings not {dv!r}"
+            elif not isinstance(dv, str):
                 return f"Dictionary element {k} must be a string not {dv!r}"
     # We know that otherwise we have an EnvironmentVariables object or None, and
     # we're okay at this point
     return None
 
+def _options_validator(value: T.Union[EnvironmentVariables, T.List['TYPE_var'], T.Dict[str, 'TYPE_var'], str, None]) -> T.Optional[str]:
+    # Reusing the env validator is a littl overkill, but nicer than duplicating the code
+    return _env_validator(value, allow_dict_list=False)
 
 def split_equal_string(input: str) -> T.Tuple[str, str]:
     """Split a string in the form `x=y`
@@ -167,18 +179,25 @@ def split_equal_string(input: str) -> T.Tuple[str, str]:
     a, b = input.split('=', 1)
     return (a, b)
 
+_FullEnvInitValueType = T.Union[EnvironmentVariables, T.List[str], T.List[T.List[str]], EnvInitValueType, str, None]
 
-def _env_convertor(value: T.Union[EnvironmentVariables, T.List[str], T.List[T.List[str]], T.Dict[str, str], str, None]) -> EnvironmentVariables:
+# Split _env_convertor() and env_convertor_with_method() to make mypy happy.
+# It does not want extra arguments in KwargInfo convertor callable.
+def env_convertor_with_method(value: _FullEnvInitValueType,
+                              init_method: Literal['set', 'prepend', 'append'] = 'set',
+                              separator: str = os.pathsep) -> EnvironmentVariables:
     if isinstance(value, str):
-        return EnvironmentVariables(dict([split_equal_string(value)]))
+        return EnvironmentVariables(dict([split_equal_string(value)]), init_method, separator)
     elif isinstance(value, list):
-        return EnvironmentVariables(dict(split_equal_string(v) for v in listify(value)))
+        return EnvironmentVariables(dict(split_equal_string(v) for v in listify(value)), init_method, separator)
     elif isinstance(value, dict):
-        return EnvironmentVariables(value)
+        return EnvironmentVariables(value, init_method, separator)
     elif value is None:
         return EnvironmentVariables()
     return value
 
+def _env_convertor(value: _FullEnvInitValueType) -> EnvironmentVariables:
+    return env_convertor_with_method(value)
 
 ENV_KW: KwargInfo[T.Union[EnvironmentVariables, T.List, T.Dict, str, None]] = KwargInfo(
     'env',
@@ -230,8 +249,7 @@ OVERRIDE_OPTIONS_KW: KwargInfo[T.List[str]] = KwargInfo(
     ContainerTypeInfo(list, str),
     listify=True,
     default=[],
-    # Reusing the env validator is a littl overkill, but nicer than duplicating the code
-    validator=_env_validator,
+    validator=_options_validator,
     convertor=_override_options_convertor,
 )
 
@@ -309,5 +327,10 @@ DEFAULT_OPTIONS: KwargInfo[T.List[str]] = KwargInfo(
     ContainerTypeInfo(list, (str, IncludeDirs)),
     listify=True,
     default=[],
-    validator=_env_validator,
+    validator=_options_validator,
 )
+
+ENV_METHOD_KW = KwargInfo('method', str, default='set', since='0.62.0',
+    validator=in_set_validator({'set', 'prepend', 'append'}))
+
+ENV_SEPARATOR_KW = KwargInfo('separator', str, default=os.pathsep, since='0.62.0')
diff --git a/test cases/unit/91 devenv/meson.build b/test cases/unit/91 devenv/meson.build
index 90c4cee..f5c24d8 100644
--- a/test cases/unit/91 devenv/meson.build
+++ b/test cases/unit/91 devenv/meson.build
@@ -11,6 +11,11 @@ env = environment()
 env.append('TEST_B', ['2', '3'], separator: '+')
 meson.add_devenv(env)
 
+meson.add_devenv({'TEST_B': '0'}, separator: '+', method: 'prepend')
+
+env = environment({'TEST_B': ['4']}, separator: '+', method: 'append')
+meson.add_devenv(env)
+
 # This exe links on a library built in another directory. On Windows this means
 # PATH must contain builddir/subprojects/sub to be able to run it.
 executable('app', 'main.c', dependencies: foo_dep, install: true)
diff --git a/test cases/unit/91 devenv/test-devenv.py b/test cases/unit/91 devenv/test-devenv.py
index de7eec2..8273805 100755
--- a/test cases/unit/91 devenv/test-devenv.py
+++ b/test cases/unit/91 devenv/test-devenv.py
@@ -6,7 +6,7 @@ from pathlib import Path
 assert os.environ['MESON_DEVENV'] == '1'
 assert os.environ['MESON_PROJECT_NAME'] == 'devenv'
 assert os.environ['TEST_A'] == '1'
-assert os.environ['TEST_B'] == '1+2+3'
+assert os.environ['TEST_B'] == '0+1+2+3+4'
 
 from mymod.mod import hello
 assert hello == 'world'