3 files changed, 46 insertions, 6 deletions
diff --git a/src/engine/SCons/Script/SConscript.py b/src/engine/SCons/Script/SConscript.py
index db6552c..5968346 100644
--- a/src/engine/SCons/Script/SConscript.py
+++ b/src/engine/SCons/Script/SConscript.py
@@ -153,6 +153,27 @@ def Return(*vars, **kw):
 
 stack_bottom = '% Stack boTTom %' # hard to define a variable w/this name :)
 
+def handle_missing_SConscript(f, must_exist):
+    """Take appropriate action on missing file in SConscript() call.
+
+    The action may be to raise an exception, or print a warning.
+    On first warning, also print a deprecation warning.
+    """
+
+    if SCons.Script._no_missing_sconscript or must_exist:
+        msg = "Fatal: missing SConscript '%s'" % f.get_internal_path()
+        raise SCons.Errors.UserError(msg)
+
+    if SCons.Script._warn_missing_sconscript_deprecated:
+        msg = "Calling missing SConscripts without error is deprecated.\n" + \
+              "Transition by adding must_exist=0 to SConscript calls.\n" + \
+              "Missing SConscript '%s'" % f.get_internal_path()
+        SCons.Warnings.warn(SCons.Warnings.DeprecatedMissingSConscriptWarning, msg)
+        SCons.Script._warn_missing_sconscript_deprecated = False
+    else:
+        msg = "Ignoring missing SConscript '%s'" % f.get_internal_path()
+        SCons.Warnings.warn(SCons.Warnings.MissingSConscriptWarning, msg)
+
 def _SConscript(fs, *files, **kw):
     top = fs.Top
     sd = fs.SConstruct_dir.rdir()
@@ -264,8 +285,7 @@ def _SConscript(fs, *files, **kw):
                         if old_file is not None:
                             call_stack[-1].globals.update({__file__:old_file})
                 else:
-                    SCons.Warnings.warn(SCons.Warnings.MissingSConscriptWarning,
-                             "Ignoring missing SConscript '%s'" % f.get_internal_path())
+                    handle_missing_SConscript(f, kw.get('must_exist', False))
 
         finally:
             SCons.Script.sconscript_reading = SCons.Script.sconscript_reading - 1
diff --git a/src/engine/SCons/Script/SConscript.xml b/src/engine/SCons/Script/SConscript.xml
index 8553fbe..29a89c2 100644
--- a/src/engine/SCons/Script/SConscript.xml
+++ b/src/engine/SCons/Script/SConscript.xml
@@ -357,12 +357,12 @@ Return('val1 val2')
 
 <scons_function name="SConscript">
 <arguments>
-(scripts, [exports, variant_dir, duplicate])
-<!-- (scripts, [exports, variant_dir, src_dir, duplicate]) -->
+(scripts, [exports, variant_dir, duplicate, must_exist=flag])
+<!-- (scripts, [exports, variant_dir, src_dir, duplicate, must_exist=flag]) -->
 </arguments>
 <arguments>
-(dirs=subdirs, [name=script, exports, variant_dir, duplicate])
-<!-- (dirs=subdirs, [name=script, exports, variant_dir, src_dir, duplicate]) -->
+(dirs=subdirs, [name=script, exports, variant_dir, duplicate, must_exist=flag])
+<!-- (dirs=subdirs, [name=script, exports, variant_dir, src_dir, duplicate, must_exist=flag]) -->
 </arguments>
 <summary>
 <para>
@@ -562,6 +562,16 @@ and what about this alternative?
 TODO??? SConscript('build/SConscript', src_dir='src')
 -->
 </para>
+<para>
+The optional
+<varname>must_exist</varname>
+argument, if true, causes an exception to be raised if a requested
+&SConscript; file is not found. The default is false,
+which only prints a warning, but this behavior is deprecated.
+For scripts which truly intend to be optional, transition to
+explicty supplying
+<literal>must_exist=False</literal> to the call.
+</para>
 
 <para>
 Here are some composite examples:
diff --git a/src/engine/SCons/Script/__init__.py b/src/engine/SCons/Script/__init__.py
index 89fc061..90bc311 100644
--- a/src/engine/SCons/Script/__init__.py
+++ b/src/engine/SCons/Script/__init__.py
@@ -276,6 +276,16 @@ def HelpFunction(text, append=False):
 # Will be non-zero if we are reading an SConscript file.
 sconscript_reading = 0
 
+_no_missing_sconscript = False
+_warn_missing_sconscript_deprecated = True
+
+def set_missing_sconscript_error(flag=1):
+    """Set behavior on missing file in SConscript() call. Returns previous value"""
+    global _no_missing_sconscript
+    old = _no_missing_sconscript
+    _no_missing_sconscript = flag
+    return old
+
 #
 def Variables(files=[], args=ARGUMENTS):
     return SCons.Variables.Variables(files, args)