From f3a8f9c34d95d862fb4d12869a7b31cea592561f Mon Sep 17 00:00:00 2001
From: Dylan Baker <dylan@pnwbakers.com>
Date: Tue, 5 Jun 2018 08:33:36 -0700
Subject: [PATCH] Options: treat array option -Dopt= and -Dopt=[] as equivalent

Currently the former will be parsed as [''], while the latter is parsed
as [] in python. This makes for some obnoxious special handling
depending on what the user passes. This is even more obnoxious since for
string type arguments this doesn't require special handling.
---
 docs/markdown/Build-options.md             |  3 +++
 docs/markdown/snippets/empty-array-opts.md |  5 +++++
 mesonbuild/coredata.py                     |  2 ++
 run_unittests.py                           | 20 ++++++++++++++++++++
 4 files changed, 30 insertions(+)
 create mode 100644 docs/markdown/snippets/empty-array-opts.md

diff --git a/docs/markdown/Build-options.md b/docs/markdown/Build-options.md
index 0093a1b222d1..66c9cb5fcec9 100644
--- a/docs/markdown/Build-options.md
+++ b/docs/markdown/Build-options.md
@@ -61,6 +61,9 @@ empty. The `value` parameter specifies the default value of the option
 and if it is unset then the values of `choices` will be used as the
 default.
 
+As of 0.47.0 -Dopt= and -Dopt=[] both pass an empty list, before this -Dopt=
+would pass a list with an empty string.
+
 This type is available since version 0.44.0
 
 ### Features
diff --git a/docs/markdown/snippets/empty-array-opts.md b/docs/markdown/snippets/empty-array-opts.md
new file mode 100644
index 000000000000..6d3b05d7261c
--- /dev/null
+++ b/docs/markdown/snippets/empty-array-opts.md
@@ -0,0 +1,5 @@
+## Array options treat -Dopt= and -Dopt=[] as equivalent
+
+Prior to this change passing -Dopt= to an array opt would be interpreted as
+[''] (an array with an empty string), now -Dopt= is the same as -Dopt=[], an
+empty list.
diff --git a/mesonbuild/coredata.py b/mesonbuild/coredata.py
index f075e75e0c90..560ebf6e6fda 100644
--- a/mesonbuild/coredata.py
+++ b/mesonbuild/coredata.py
@@ -154,6 +154,8 @@ def validate_value(self, value, user_input=True):
         if isinstance(value, str):
             if value.startswith('['):
                 newvalue = ast.literal_eval(value)
+            elif value == '':
+                newvalue = []
             else:
                 if self.shlex_split:
                     newvalue = shlex.split(value)
diff --git a/run_unittests.py b/run_unittests.py
index 4cfb743730b1..0abe419e6dfa 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -1786,6 +1786,26 @@ def get_opt():
         changed = get_opt()
         self.assertDictEqual(changed, expected)
 
+    def test_array_option_empty_equivalents(self):
+        """Array options treat -Dopt=[] and -Dopt= as equivalent."""
+        def get_opt():
+            opts = self.introspect('--buildoptions')
+            for x in opts:
+                if x.get('name') == 'list':
+                    return x
+            raise Exception(opts)
+
+        expected = {
+            'name': 'list',
+            'description': 'list',
+            'type': 'array',
+            'value': [],
+        }
+        tdir = os.path.join(self.unit_test_dir, '18 array option')
+        self.init(tdir, extra_args='-Dlist=')
+        original = get_opt()
+        self.assertDictEqual(original, expected)
+
     def opt_has(self, name, value):
         res = self.introspect('--buildoptions')
         found = False