dependency: Empty fallback is the same as allow_fallback: false

docs/markdown/Reference-manual.md

@@ -515,6 +515,8 @@ This function supports the following keyword arguments:
   in this case the subproject must use
   `meson.override_dependency('dependency_name', subproj_dep)`
   to specify the dependency object used in the superproject.
+  If the value is an empty list, it has the same effect as
+  `allow_fallback: false`.
 - `language` *(since 0.42.0)*: defines what language-specific
   dependency to find if it's available for multiple languages.
 - `method`: defines the way the dependency is detected, the default is

mesonbuild/interpreter/dependencyfallbacks.py

@@ -47,6 +47,10 @@ class DependencyFallbacksHolder(InterpreterObject):
                              location=self.interpreter.current_node)
             return
         fbinfo = stringlistify(fbinfo)
+        if len(fbinfo) == 0:
+            # dependency('foo', fallback: []) is the same as dependency('foo', allow_fallback: false)
+            self.allow_fallback = False
+            return
         if len(fbinfo) == 1:
             FeatureNew.single_use('Fallback without variable name', '0.53.0', self.subproject)
             subp_name, varname = fbinfo[0], None

test cases/failing/115 empty fallback/meson.build

@@ -0,0 +1,6 @@
+project('empty fallback')
+
+# There is a subproject named 'foo' that overrides that dependency,
+# but `fallback: []` should not allow to use it. Same behaviour than with
+# `allow_fallback: false`
+dependency('foo', fallback: [])

test cases/failing/115 empty fallback/subprojects/foo/meson.build

@@ -0,0 +1,3 @@
+project('foo')
+
+meson.override_dependency('foo', declare_dependency())

test cases/failing/115 empty fallback/test.json

@@ -0,0 +1,7 @@
+{
+    "stdout": [
+        {
+            "line": "test cases/failing/115 empty fallback/meson.build:6:0: ERROR: Dependency \"foo\" not found, tried pkgconfig and cmake"
+        }
+    ]
+}