Be more careful about the use of repr() in error messages

Generally, we'd want to use str() rather than repr() in error messages
anyhow, as that explicitly gives something designed to be read by
humans.

Sometimes {!r} is being used as a shortcut to avoid writing the quotes
in '{!s}'.

Unfortunately, these things aren't quite the same, as the repr of a
string containing '\' (the path separator on Windows) will have those
escaped.

We don't have a good string representation to use for the arbitrary
internal object used as an argument for install_data() when it's neither
a string nor file (which doesn't lead to a good error message), so drop
that for the moment.

mesonbuild/build.py

@@ -531,6 +531,9 @@ class BuildTarget(Target):
         repr_str = "<{0} {1}: {2}>"
         return repr_str.format(self.__class__.__name__, self.get_id(), self.filename)
 
+    def __str__(self):
+        return "{}".format(self.name)
+
     def validate_install(self, environment):
         if self.for_machine is MachineChoice.BUILD and self.need_install:
             if environment.is_cross_build():
@@ -1104,7 +1107,7 @@ You probably should put it in link_with instead.''')
             if not isinstance(t, (Target, CustomTargetIndex)):
                 raise InvalidArguments('{!r} is not a target.'.format(t))
             if not t.is_linkable_target():
-                raise InvalidArguments('Link target {!r} is not linkable.'.format(t))
+                raise InvalidArguments("Link target '{!s}' is not linkable.".format(t))
             if isinstance(self, SharedLibrary) and isinstance(t, StaticLibrary) and not t.pic:
                 msg = "Can't link non-PIC static library {!r} into shared library {!r}. ".format(t.name, self.name)
                 msg += "Use the 'pic' option to static_library to build with PIC."

mesonbuild/coredata.py

@@ -490,7 +490,7 @@ class CoreData:
             # commonpath will always return a path in the native format, so we
             # must use pathlib.PurePath to do the same conversion before
             # comparing.
-            msg = ('The value of the {!r} option is {!r} which must be a '
+            msg = ('The value of the {!r} option is \'{!s}\' which must be a '
                    'subdir of the prefix {!r}.\nNote that if you pass a '
                    'relative path, it is assumed to be a subdir of prefix.')
             # os.path.commonpath doesn't understand case-insensitive filesystems,

mesonbuild/interpreter.py

@@ -3897,7 +3897,7 @@ This will become a hard error in the future.''' % kwargs['input'], location=self
         absname = os.path.join(self.environment.get_source_dir(), buildfilename)
         if not os.path.isfile(absname):
             self.subdir = prev_subdir
-            raise InterpreterException('Non-existent build file {!r}'.format(buildfilename))
+            raise InterpreterException("Non-existent build file '{!s}'".format(buildfilename))
         with open(absname, encoding='utf8') as f:
             code = f.read()
         assert(isinstance(code, str))
@@ -3945,7 +3945,7 @@ This will become a hard error in the future.''' % kwargs['input'], location=self
             elif isinstance(s, str):
                 source_strings.append(s)
             else:
-                raise InvalidArguments('Argument {!r} must be string or file.'.format(s))
+                raise InvalidArguments('Argument must be string or file.')
         sources += self.source_strings_to_files(source_strings)
         install_dir = kwargs.get('install_dir', None)
         if not isinstance(install_dir, (str, type(None))):