interpreter: Dependency variables can be empty string

There is no reason to forbid empty variables, PkgConfigCLI.variable()
even has code specifically for handling that case.

3 files changed, 4 insertions, 2 deletions

diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index aaffec0b9..99c4f9625 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -702,6 +702,8 @@ class Interpreter(InterpreterBase, HoldableObject):
         srcdir = Path(self.environment.source_dir)
         # convert variables which refer to an -uninstalled.pc style datadir
         for k, v in variables.items():
+            if not v:
+                FeatureNew.single_use('empty variable value in declare_dependency', '1.4.0', self.subproject, location=node)
             try:
                 p = Path(v)
             except ValueError:
diff --git a/mesonbuild/interpreter/type_checking.py b/mesonbuild/interpreter/type_checking.py
index 616f4efbb..2ec7d58ce 100644
--- a/mesonbuild/interpreter/type_checking.py
+++ b/mesonbuild/interpreter/type_checking.py
@@ -144,8 +144,6 @@ def variables_validator(contents: T.Union[str, T.List[str], T.Dict[str, str]]) -
     for k, v in variables.items():
         if not k:
             return 'empty variable name'
-        if not v:
-            return 'empty variable value'
         if any(c.isspace() for c in k):
             return f'invalid whitespace in variable name {k!r}'
     return None
diff --git a/mesonbuild/modules/pkgconfig.py b/mesonbuild/modules/pkgconfig.py
index 3f9ce7b71..ebe0d92d5 100644
--- a/mesonbuild/modules/pkgconfig.py
+++ b/mesonbuild/modules/pkgconfig.py
@@ -680,6 +680,8 @@ class PkgConfigModule(NewExtensionModule):
             reserved = ['prefix', 'libdir', 'includedir']
             variables = []
             for name, value in vardict.items():
+                if not value:
+                    FeatureNew.single_use('empty variable value in pkg.generate', '1.4.0', state.subproject, location=state.current_node)
                 if not dataonly and name in reserved:
                     raise mesonlib.MesonException(f'Variable "{name}" is reserved')
                 variables.append((name, value))