From 5f3b73beb594b837e7b817b570c0a722c9cc2f63 Mon Sep 17 00:00:00 2001
From: Xavier Claessens <xavier.claessens@collabora.com>
Date: Thu, 17 Jun 2021 14:41:55 -0400
Subject: [PATCH] dependency: Empty fallback is the same as allow_fallback:
 false

---
 docs/markdown/Reference-manual.md                          | 2 ++
 mesonbuild/interpreter/dependencyfallbacks.py              | 4 ++++
 test cases/failing/115 empty fallback/meson.build          | 6 ++++++
 .../failing/115 empty fallback/subprojects/foo/meson.build | 3 +++
 test cases/failing/115 empty fallback/test.json            | 7 +++++++
 5 files changed, 22 insertions(+)
 create mode 100644 test cases/failing/115 empty fallback/meson.build
 create mode 100644 test cases/failing/115 empty fallback/subprojects/foo/meson.build
 create mode 100644 test cases/failing/115 empty fallback/test.json

diff --git a/docs/markdown/Reference-manual.md b/docs/markdown/Reference-manual.md
index 18f30b32d..fec4e7417 100644
--- a/docs/markdown/Reference-manual.md
+++ b/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
diff --git a/mesonbuild/interpreter/dependencyfallbacks.py b/mesonbuild/interpreter/dependencyfallbacks.py
index 6edb129ab..5b78d2073 100644
--- a/mesonbuild/interpreter/dependencyfallbacks.py
+++ b/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
diff --git a/test cases/failing/115 empty fallback/meson.build b/test cases/failing/115 empty fallback/meson.build
new file mode 100644
index 000000000..f4eb5feb9
--- /dev/null
+++ b/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: [])
diff --git a/test cases/failing/115 empty fallback/subprojects/foo/meson.build b/test cases/failing/115 empty fallback/subprojects/foo/meson.build
new file mode 100644
index 000000000..c9e134b5e
--- /dev/null
+++ b/test cases/failing/115 empty fallback/subprojects/foo/meson.build	
@@ -0,0 +1,3 @@
+project('foo')
+
+meson.override_dependency('foo', declare_dependency())
diff --git a/test cases/failing/115 empty fallback/test.json b/test cases/failing/115 empty fallback/test.json
new file mode 100644
index 000000000..dcfde45c4
--- /dev/null
+++ b/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"
+        }
+    ]
+}