devenv: Add --dump option

It prints all envorinmente variables that have been modified. Can be
used by shell scripts that wish to setup their environment themself.

docs/markdown/snippets/devenv.md

@@ -16,3 +16,8 @@ a library name that matches one being built, Meson adds the needed auto-load
 commands into `<builddir>/.gdbinit` file. When running gdb from top build
 directory, that file is loaded by gdb automatically.
 
+## Print modified environment variables with `meson devenv --dump`
+
+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.

mesonbuild/build.py

@@ -476,6 +476,9 @@ class EnvironmentVariables(HoldableObject):
     def has_name(self, name: str) -> bool:
         return name in self.varnames
 
+    def get_names(self) -> T.Set[str]:
+        return self.varnames
+
     def set(self, name: str, values: T.List[str], separator: str = os.pathsep) -> None:
         self.varnames.add(name)
         self.envvars.append((self._set, name, values, separator))

mesonbuild/mdevenv.py

@@ -2,10 +2,11 @@ import os, subprocess
 import argparse
 import tempfile
 import shutil
+import itertools
 
 from pathlib import Path
 from . import build, minstall, dependencies
-from .mesonlib import MesonException, RealPathAction, is_windows, setup_vsenv, OptionKey
+from .mesonlib import MesonException, RealPathAction, is_windows, setup_vsenv, OptionKey, quote_arg
 from . import mlog
 
 import typing as T
@@ -14,7 +15,9 @@ if T.TYPE_CHECKING:
 
 def add_arguments(parser: argparse.ArgumentParser) -> None:
     parser.add_argument('-C', dest='wd', action=RealPathAction,
-                        help='directory to cd into before running')
+                        help='Directory to cd into before running')
+    parser.add_argument('--dump', action='store_true',
+                        help='Only print required environment (Since 0.62.0)')
     parser.add_argument('command', nargs=argparse.REMAINDER,
                         help='Command to run in developer environment (default: interactive shell)')
 
@@ -25,11 +28,7 @@ def get_windows_shell() -> str:
     result = subprocess.check_output(command)
     return result.decode().strip()
 
-def get_env(b: build.Build, build_dir: str) -> T.Dict[str, str]:
+def get_env(b: build.Build, build_dir: str) -> T.Tuple[T.Dict[str, str], T.Set[str]]:
-    env = os.environ.copy()
-    for i in b.devenv:
-        env = i.get_env(env)
-
     extra_env = build.EnvironmentVariables()
     extra_env.set('MESON_DEVENV', ['1'])
     extra_env.set('MESON_PROJECT_NAME', [b.project_name])
@@ -38,7 +37,13 @@ def get_env(b: build.Build, build_dir: str) -> T.Dict[str, str]:
     if meson_uninstalled.is_dir():
         extra_env.prepend('PKG_CONFIG_PATH', [str(meson_uninstalled)])
 
-    return extra_env.get_env(env)
+    env = os.environ.copy()
+    varnames = set()
+    for i in itertools.chain(b.devenv, {extra_env}):
+        env = i.get_env(env)
+        varnames |= i.get_names()
+
+    return env, varnames
 
 def bash_completion_files(b: build.Build, install_data: 'InstallData') -> T.List[str]:
     result = []
@@ -108,12 +113,21 @@ def run(options: argparse.Namespace) -> int:
     if not buildfile.is_file():
         raise MesonException(f'Directory {options.wd!r} does not seem to be a Meson build directory.')
     b = build.load(options.wd)
-    install_data = minstall.load_install_data(str(privatedir / 'install.dat'))
-    setup_vsenv(b.need_vsenv)
 
-    devenv = get_env(b, options.wd)
+    devenv, varnames = get_env(b, options.wd)
+    if options.dump:
+        if options.command:
+            raise MesonException('--dump option does not allow running other command.')
+        for name in varnames:
+            print(f'{name}={quote_arg(devenv[name])}')
+            print(f'export {name}')
+        return 0
+
+    install_data = minstall.load_install_data(str(privatedir / 'install.dat'))
     write_gdb_script(privatedir, install_data)
 
+    setup_vsenv(b.need_vsenv)
+
     args = options.command
     if not args:
         prompt_prefix = f'[{b.project_name}]'