The default value of required is true for dependencies.

dependencies.py

@@ -155,7 +155,9 @@ class ExternalLibrary(Dependency):
         return []
 
 def find_external_dependency(name, kwargs):
-    required = kwargs.get('required', False)
+    required = kwargs.get('required', True)
+    if not isinstance(required, bool):
+        raise DependencyException('Keyword "required" must be a boolean.')
     if name in packages:
         dep = packages[name](kwargs)
         if required and not dep.found():

test cases/frameworks/1 boost/meson.build

@@ -4,8 +4,8 @@ project('boosttest', 'cxx')
 # within one project. The need to be independent of each other.
 # Use one without a library dependency and one with it.
 
-nolinkdep = find_dep('boost', modules: 'utility', required : true)
+nolinkdep = find_dep('boost', modules: 'utility')
-linkdep = find_dep('boost', modules : 'thread', required : true)
+linkdep = find_dep('boost', modules : 'thread')
 
 nolinkexe = executable('nolinkedexe', 'nolinkexe.cc', deps : nolinkdep)
 linkexe = executable('linkedexe', 'linkexe.cc', deps : linkdep)

test cases/frameworks/2 gtest/meson.build

@@ -1,6 +1,6 @@
 project('gtest', 'cxx')
 
-gtest = find_dep('gtest', required : true)
+gtest = find_dep('gtest')
 
 e = executable('testprog', 'test.cc', deps : gtest)
 add_test('gtest test', e)

test cases/frameworks/3 gmock/meson.build

@@ -3,8 +3,8 @@ project('gmock test', 'cxx')
 # Using gmock without gtest is a pain so just
 # don't support that then.
 
-gtest = find_dep('gtest', required : true)
+gtest = find_dep('gtest')
-gmock = find_dep('gmock', required : true)
+gmock = find_dep('gmock')
 
 e = executable('gmocktest', 'gmocktest.cc', deps : [gtest, gmock])
 add_test('gmock test', e)

test cases/frameworks/4 qt5/meson.build

@@ -1,6 +1,6 @@
 project('qt5 build test', 'cxx')
 
-qt5dep = find_dep('qt5', modules : 'Widgets', required : true)
+qt5dep = find_dep('qt5', modules : 'Widgets')
 
 q5exe = executable('qt5test',
 sources : ['main.cpp', 'mainWindow.cpp'], # Sources that don't need preprocessing.

test cases/frameworks/5 protocol buffers/meson.build

@@ -1,7 +1,7 @@
 project('protocol buffer test', 'cxx')
 
 protoc = find_program('protoc', required : true)
-dep = find_dep('protobuf', required : true)
+dep = find_dep('protobuf')
 
 gen = generator(protoc, \
   outputs  : ['@BASENAME@.pb.cc', '@BASENAME@.pb.h'],

test cases/linuxlike/1 pkg-config/meson.build

@@ -2,7 +2,11 @@ project('external dependency', 'c')
 
 # Zlib is probably on all dev machines.
 
-dep = find_dep('zlib', required : true)
+dep = find_dep('zlib')
 exe = executable('zlibprog', 'prog.c', deps : dep)
 
 add_test('zlibtest', exe)
+
+# Try to find a nonexistant library to ensure requires:false works.
+
+dep = find_dep('nvakuhrabnsdfasdf', required : false)

test cases/objc/2 nsstring/meson.build

@@ -1,9 +1,9 @@
 project('nsstring', 'objc')
 
 if host.name() == 'darwin'
-  dep = find_dep('appleframeworks', modules : 'foundation', required : true)
+  dep = find_dep('appleframeworks', modules : 'foundation')
 else
-  dep = find_dep('gnustep', required : true)
+  dep = find_dep('gnustep')
 endif
 exe = executable('stringprog', 'stringprog.m', deps : dep)
 add_test('stringtest', exe)