Print a more usable message when a subproject fails to configure

Instead of just printing the message in the exception, if it's
a MesonException, also print the file and the line number. If it's an
unknown exception, print the entire traceback so that we can pin-point
what the Meson bug causing it is.

4 files changed, 24 insertions, 8 deletions

diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index 121fdb7..833e982 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -36,6 +36,7 @@ import re, shlex
 import subprocess
 from collections import namedtuple
 from pathlib import PurePath
+import traceback
 
 import importlib
 
@@ -2960,9 +2961,14 @@ root and issuing %s.
         # If the subproject execution failed in a non-fatal way, don't raise an
         # exception; let the caller handle things.
         except Exception as e:
-            mlog.log('Couldn\'t use fallback subproject in',
-                     mlog.bold(os.path.join(self.subproject_dir, dirname)),
-                     'for the dependency', mlog.bold(display_name), '\nReason:', str(e))
+            msg = ['Couldn\'t use fallback subproject in',
+                   mlog.bold(os.path.join(self.subproject_dir, dirname)),
+                   'for the dependency', mlog.bold(display_name), '\nReason:']
+            if isinstance(e, mesonlib.MesonException):
+                msg.append(e.get_msg_with_context())
+            else:
+                msg.append(traceback.format_exc())
+            mlog.log(*msg)
             return None
         dep = self.get_subproject_dep(name, dirname, varname, kwargs.get('required', True))
         if not dep:
diff --git a/mesonbuild/interpreterbase.py b/mesonbuild/interpreterbase.py
index dfdccb1..64177ab 100644
--- a/mesonbuild/interpreterbase.py
+++ b/mesonbuild/interpreterbase.py
@@ -394,7 +394,7 @@ class InterpreterBase:
                 self.current_lineno = cur.lineno
                 self.evaluate_statement(cur)
             except Exception as e:
-                if not(hasattr(e, 'lineno')):
+                if not hasattr(e, 'lineno'):
                     e.lineno = cur.lineno
                     e.colno = cur.colno
                     e.file = os.path.join(self.subdir, 'meson.build')
diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index f3682ce..efb8d11 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -83,6 +83,13 @@ an_unpicklable_object = threading.Lock()
 class MesonException(Exception):
     '''Exceptions thrown by Meson'''
 
+    def get_msg_with_context(self):
+        s = ''
+        if hasattr(self, 'lineno') and hasattr(self, 'file'):
+            s = get_error_location_string(self.file, self.lineno) + ' '
+        s += str(self)
+        return s
+
 class EnvironmentException(MesonException):
     '''Exceptions thrown while processing and creating the build environment'''
 
@@ -1047,6 +1054,9 @@ def detect_subprojects(spdir_name, current_dir='', result=None):
                 result[basename] = [trial]
     return result
 
+def get_error_location_string(fname, lineno):
+    return '{}:{}:'.format(fname, lineno)
+
 class OrderedSet(collections.MutableSet):
     """A set that preserves the order in which items are added, by first
     insertion.
diff --git a/mesonbuild/mlog.py b/mesonbuild/mlog.py
index b75a267..1654824 100644
--- a/mesonbuild/mlog.py
+++ b/mesonbuild/mlog.py
@@ -140,7 +140,8 @@ def log(*args, **kwargs):
     force_print(*arr, **kwargs)
 
 def _log_error(severity, *args, **kwargs):
-    from . import environment
+    from .mesonlib import get_error_location_string
+    from .environment import build_filename
     if severity == 'warning':
         args = (yellow('WARNING:'),) + args
     elif severity == 'error':
@@ -152,9 +153,8 @@ def _log_error(severity, *args, **kwargs):
 
     location = kwargs.pop('location', None)
     if location is not None:
-        location_str = '{}:{}:'.format(os.path.join(location.subdir,
-                                                    environment.build_filename),
-                                       location.lineno)
+        location_file = os.path.join(location.subdir, build_filename)
+        location_str = get_error_location_string(location_file, location.lineno)
         args = (location_str,) + args
 
     log(*args, **kwargs)