interpreter: Warn when environment() ops are overridenwarn-env-ops-dont-stack

Warn when someone tries to use append() or prepend() on an env var
which already has an operation set on it. People seem to think that
multiple append/prepend operations stack, but they don't.

Closes https://github.com/mesonbuild/meson/issues/5087

1 files changed, 9 insertions, 0 deletions

diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 020c47b58..dae94b6ed 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -296,11 +296,20 @@ class ExtractedObjects:
 class EnvironmentVariables:
     def __init__(self):
         self.envvars = []
+        # The set of all env vars we have operations for. Only used for self.has_name()
+        self.varnames = set()
 
     def __repr__(self):
         repr_str = "<{0}: {1}>"
         return repr_str.format(self.__class__.__name__, self.envvars)
 
+    def add_var(self, method, name, args, kwargs):
+        self.varnames.add(name)
+        self.envvars.append((method, name, args, kwargs))
+
+    def has_name(self, name):
+        return name in self.varnames
+
     def get_value(self, values, kwargs):
         separator = kwargs.get('separator', os.pathsep)