Improve error when using the dependencies kwarg

The error message is misleading (talks about external dependencies), and
doesn't tell you what you need to do (use the output of
declare_dependency, dependency, or find_library). At the same time
rename add_external_deps to add_deps since it adds internal deps too.

Plus many more error message improvements all over the place.

mesonbuild/build.py

@@ -514,7 +514,7 @@ class BuildTarget():
         deplist = kwargs.get('dependencies', [])
         if not isinstance(deplist, list):
             deplist = [deplist]
-        self.add_external_deps(deplist)
+        self.add_deps(deplist)
         self.custom_install_dir = kwargs.get('install_dir', None)
         if self.custom_install_dir is not None:
             if not isinstance(self.custom_install_dir, str):
@@ -644,7 +644,7 @@ class BuildTarget():
     def get_include_dirs(self):
         return self.include_dirs
 
-    def add_external_deps(self, deps):
+    def add_deps(self, deps):
         if not isinstance(deps, list):
             deps = [deps]
         for dep in deps:
@@ -664,7 +664,7 @@ class BuildTarget():
                                                           [], [], [])
                 self.external_deps.append(extpart)
                 # Deps of deps.
-                self.add_external_deps(dep.ext_deps)
+                self.add_deps(dep.ext_deps)
             elif isinstance(dep, dependencies.Dependency):
                 self.external_deps.append(dep)
                 self.process_sourcelist(dep.get_sources())
@@ -673,10 +673,13 @@ class BuildTarget():
                 # about the interpreter so we can't import it and use isinstance.
                 # This should be reliable enough.
                 if hasattr(dep, 'subproject'):
-                    raise InvalidArguments('''Tried to use subproject object as a dependency.
-You probably wanted to use a dependency declared in it instead. Access it
-by calling get_variable() on the subproject object.''')
-                raise InvalidArguments('Argument is not an external dependency.')
+                    raise InvalidArguments('Tried to use subproject object as a dependency.\n'
+                            'You probably wanted to use a dependency declared in it instead.\n'
+                            'Access it by calling get_variable() on the subproject object.')
+                raise InvalidArguments('Argument is of an unacceptable type {!r}.\nMust be '
+                        'either an external dependency (returned by find_library() or '
+                        'dependency()) or an internal dependency (returned by '
+                        'declare_dependency()).'.format(type(dep).__name__))
 
     def get_external_deps(self):
         return self.external_deps
@@ -702,7 +705,7 @@ by calling get_variable() on the subproject object.''')
             return
         elif len(pchlist) == 1:
             if not environment.is_header(pchlist[0]):
-                raise InvalidArguments('Pch argument %s is not a header.' % pchlist[0])
+                raise InvalidArguments('PCH argument %s is not a header.' % pchlist[0])
         elif len(pchlist) == 2:
             if environment.is_header(pchlist[0]):
                 if not environment.is_source(pchlist[1]):
@@ -745,8 +748,7 @@ by calling get_variable() on the subproject object.''')
 class Generator():
     def __init__(self, args, kwargs):
         if len(args) != 1:
-            raise InvalidArguments('Generator requires one and only one positional argument')
-
+            raise InvalidArguments('Generator requires exactly one positional argument: the executable')
         exe = args[0]
         if hasattr(exe, 'held_object'):
             exe = exe.held_object
@@ -1168,8 +1170,7 @@ class CustomTarget:
                 raise InvalidArguments('Output must not contain a path segment.')
         self.capture = kwargs.get('capture', False)
         if self.capture and len(self.output) != 1:
-            raise InvalidArguments(
-                'Capturing can only output to a single file.')
+            raise InvalidArguments('Capturing can only output to a single file.')
         if 'command' not in kwargs:
             raise InvalidArguments('Missing keyword argument "command".')
         if 'depfile' in kwargs:
@@ -1190,7 +1191,7 @@ class CustomTarget:
                 final_cmd.append(c)
             elif isinstance(c, dependencies.ExternalProgram):
                 if not c.found():
-                    raise InvalidArguments('Tried to use not found external program in a build rule.')
+                    raise InvalidArguments('Tried to use not found external program {!r} in a build rule.'.format(c.name))
                 final_cmd += c.get_command()
             elif isinstance(c, (BuildTarget, CustomTarget)):
                 self.dependencies.append(c)
@@ -1231,7 +1232,7 @@ class CustomTarget:
             while hasattr(ed, 'held_object'):
                 ed = ed.held_object
             if not isinstance(ed, (CustomTarget, BuildTarget)):
-                raise InvalidArguments('Can only depend on toplevel targets.')
+                raise InvalidArguments('Can only depend on toplevel targets: custom_target or build_target (executable or a library)')
             self.extra_depends.append(ed)
         depend_files = kwargs.get('depend_files', [])
         if not isinstance(depend_files, list):
@@ -1241,7 +1242,7 @@ class CustomTarget:
                 self.depend_files.append(i)
             else:
                 mlog.debug(i)
-                raise InvalidArguments('Unknown type in depend_files.')
+                raise InvalidArguments('Unknown type {!r} in depend_files.'.format(type(i).__name__))
 
     def get_basename(self):
         return self.name

mesonbuild/interpreter.py

@@ -1559,7 +1559,7 @@ class Interpreter():
         r = wrap.Resolver(os.path.join(self.build.environment.get_source_dir(), self.subproject_dir))
         resolved = r.resolve(dirname)
         if resolved is None:
-            msg = 'Subproject directory {!r} does not exist and can not be downloaded.'
+            msg = 'Subproject directory {!r} does not exist and cannot be downloaded.'
             raise InterpreterException(msg.format(os.path.join(self.subproject_dir, dirname)))
         subdir = os.path.join(self.subproject_dir, resolved)
         os.makedirs(os.path.join(self.build.environment.get_build_dir(), subdir), exist_ok=True)
@@ -2266,9 +2266,18 @@ requirements use the version keyword argument instead.''')
     @stringArgs
     def func_add_global_arguments(self, node, args, kwargs):
         if self.subproject != '':
-            raise InvalidCode('Global arguments can not be set in subprojects because there is no way to make that reliable.')
+            msg = 'Global arguments can not be set in subprojects because ' \
+                  'there is no way to make that reliable.\nPlease only call ' \
+                  'this if is_subproject() returns false. Alternatively, ' \
+                  'define a variable that\ncontains your language-specific ' \
+                  'arguments and add it to the appropriate *_args kwarg ' \
+                  'in each target.'
+            raise InvalidCode(msg)
         if self.global_args_frozen:
-            raise InvalidCode('Tried to set global arguments after a build target has been declared.\nThis is not permitted. Please declare all global arguments before your targets.')
+            msg = 'Tried to set global arguments after a build target has ' \
+                  'been declared.\nThis is not permitted. Please declare all ' \
+                  'global arguments before your targets.'
+            raise InvalidCode(msg)
         if not 'language' in kwargs:
             raise InvalidCode('Missing language definition in add_global_arguments')
         lang = kwargs['language'].lower()
@@ -2280,11 +2289,20 @@ requirements use the version keyword argument instead.''')
     @stringArgs
     def func_add_global_link_arguments(self, node, args, kwargs):
         if self.subproject != '':
-            raise InvalidCode('Global arguments can not be set in subprojects because there is no way to make that reliable.')
+            msg = 'Global link arguments can not be set in subprojects because ' \
+                  'there is no way to make that reliable.\nPlease only call ' \
+                  'this if is_subproject() returns false. Alternatively, ' \
+                  'define a variable that\ncontains your language-specific ' \
+                  'arguments and add it to the appropriate *_args kwarg ' \
+                  'in each target.'
+            raise InvalidCode(msg)
         if self.global_args_frozen:
-            raise InvalidCode('Tried to set global arguments after a build target has been declared.\nThis is not permitted. Please declare all global arguments before your targets.')
+            msg = 'Tried to set global link arguments after a build target has ' \
+                  'been declared.\nThis is not permitted. Please declare all ' \
+                  'global arguments before your targets.'
+            raise InvalidCode(msg)
         if not 'language' in kwargs:
-            raise InvalidCode('Missing language definition in add_global_arguments')
+            raise InvalidCode('Missing language definition in add_global_link_arguments')
         lang = kwargs['language'].lower()
         if lang in self.build.global_link_args:
             self.build.global_link_args[lang] += args
@@ -2405,7 +2423,7 @@ requirements use the version keyword argument instead.''')
         for l in self.get_used_languages(target):
             if self.environment.cross_info.has_stdlib(l) and \
                 self.subproject != self.environment.cross_info.get_stdlib(l)[0]:
-                target.add_external_deps(self.build.cross_stdlibs[l])
+                target.add_deps(self.build.cross_stdlibs[l])
 
     def check_sources_exist(self, subdir, sources):
         for s in sources:
@@ -2413,7 +2431,7 @@ requirements use the version keyword argument instead.''')
                 continue # This means a generated source and they always exist.
             fname = os.path.join(subdir, s)
             if not os.path.isfile(fname):
-                raise InterpreterException('Tried to add non-existing source %s.' % s)
+                raise InterpreterException('Tried to add non-existing source file %s.' % s)
 
     def function_call(self, node):
         func_name = node.func_name
@@ -2469,7 +2487,7 @@ requirements use the version keyword argument instead.''')
                 else:
                     return posargs[1]
             else:
-                raise InterpreterException('bool.to_string() must have either no arguments or exactly two string arguments.')
+                raise InterpreterException('bool.to_string() must have either no arguments or exactly two string arguments that signify what values to return for true and false.')
         elif method_name == 'to_int':
             if obj == True:
                 return 1
@@ -2509,7 +2527,7 @@ requirements use the version keyword argument instead.''')
             return re.sub(r'[^a-zA-Z0-9]', '_', obj)
         elif method_name == 'split':
             if len(posargs) > 1:
-                raise InterpreterException('Split()  must have at most one argument.')
+                raise InterpreterException('Split() must have at most one argument.')
             elif len(posargs) == 1:
                 s = posargs[0]
                 if not isinstance(s, str):
@@ -2530,7 +2548,7 @@ requirements use the version keyword argument instead.''')
             try:
                 return int(obj)
             except Exception:
-                raise InterpreterException('String can not be converted to int: ' + obj)
+                raise InterpreterException('String {!r} cannot be converted to int'.format(obj))
         elif method_name == 'join':
             if len(posargs) != 1:
                 raise InterpreterException('Join() takes exactly one argument.')
@@ -2635,8 +2653,7 @@ requirements use the version keyword argument instead.''')
         for i in node.ifs:
             result = self.evaluate_statement(i.condition)
             if not(isinstance(result, bool)):
-                print(result)
-                raise InvalidCode('If clause does not evaluate to true or false.')
+                raise InvalidCode('If clause {!r} does not evaluate to true or false.'.format(result))
             if result:
                 self.evaluate_codeblock(i.block)
                 return