vsenv: improve how VS vars are parsed

Use a command instead of creating a temporary file
for the .bat script and process only newly created variables

mesonbuild/utils/vsenv.py

@@ -5,8 +5,6 @@ import subprocess
 import json
 import pathlib
 import shutil
-import tempfile
-import locale
 
 from .. import mlog
 from .core import MesonException
@@ -18,14 +16,6 @@ __all__ = [
 ]
 
 
-bat_template = '''@ECHO OFF
-
-call "{}"
-
-ECHO {}
-SET
-'''
-
 # If on Windows and VS is installed but not set up in the environment,
 # set it to be runnable. In this way Meson can be directly invoked
 # from any shell, VS Code etc.
@@ -88,43 +78,41 @@ def _setup_vsenv(force: bool) -> bool:
         raise MesonException(f'Could not find {bat_path}')
 
     mlog.log('Activating VS', bat_info[0]['catalog']['productDisplayVersion'])
-    bat_separator = '---SPLIT---'
-    bat_contents = bat_template.format(bat_path, bat_separator)
-    bat_file = tempfile.NamedTemporaryFile('w', suffix='.bat', encoding='utf-8', delete=False)
-    bat_file.write(bat_contents)
-    bat_file.flush()
-    bat_file.close()
-    bat_output = subprocess.check_output(bat_file.name, universal_newlines=True,
-                                         encoding=locale.getpreferredencoding(False))
-    os.unlink(bat_file.name)
-    bat_lines = bat_output.split('\n')
-    bat_separator_seen = False
-    for bat_line in bat_lines:
-        if bat_line == bat_separator:
-            bat_separator_seen = True
-            continue
-        if not bat_separator_seen:
-            continue
-        if not bat_line:
-            continue
-        parts = bat_line.split('=', 1)
-        if len(parts) != 2:
-            continue
-        k, v = parts
-        # Some CI's include variables containing the issue description, like
-        # GitLab's CI_MERGE_REQUEST_DESCRIPTION. The description itself can
-        # have multiple lines and any kind of content.
-        # If one of these lines is '=========', it will leave k empty
-        # when it's split by '='
-        if k is None or v is None:
-            continue
-        try:
-            os.environ[k] = v
-        except ValueError:
-            # Ignore errors from junk data returning invalid environment variable names
-            pass
+
+    before_separator = '---BEFORE---'
+    after_separator = '---AFTER---'
+    # This will print to stdout the env variables set before the VS
+    # activation and after VS activation so that we can process only
+    # newly created environment variables. This is required to correctly parse
+    # environment variables taking into account that some variables
+    # can have multiple lines. (https://github.com/mesonbuild/meson/pull/13682)
+    cmd = f'set&& echo {before_separator}&&"{bat_path.absolute()}" && echo {after_separator}&& set'
+    process = subprocess.Popen(
+        f'cmd.exe /c "{cmd}"',
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        shell=True,
+    )
+    stdout, stderr = process.communicate()
+    if process.returncode != 0:
+        raise RuntimeError(f"Script failed with error: {stderr.decode()}")
+    lines = stdout.decode().splitlines()
+
+    # Remove the output from the vcvars script
+    try:
+        lines_before = lines[:lines.index(before_separator)]
+        lines_after = lines[lines.index(after_separator) + 1:]
+    except ValueError:
+        raise MesonException('Could not find separators in environment variables output')
+
+    # Filter out duplicated lines to remove env variables that haven't changed
+    new_lines = set(lines_before) - set(lines_after)
+    for line in new_lines:
+        k, v = line.split('=', 1)
+        os.environ[k] = v
     return True
 
+
 def setup_vsenv(force: bool = False) -> bool:
     try:
         return _setup_vsenv(force)