# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1530551994 -7200
# Node ID 4bf5180fbfeea4f4d505238f0f688ea306db1f95
# Parent  1b1c1664e7749321fc00bf1e5153730145894c18
Added missing sequence length check when unpacking sequences.

diff -r 1b1c1664e774 -r 4bf5180fbfee common.py
--- a/common.py	Mon Jul 02 17:53:15 2018 +0200
+++ b/common.py	Mon Jul 02 19:19:54 2018 +0200
@@ -4,7 +4,7 @@
 Common functions.
 
 Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013,
-              2014, 2015, 2016, 2017 Paul Boddie <paul@boddie.org.uk>
+              2014, 2015, 2016, 2017, 2018 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -433,7 +433,7 @@
         variable.
         """
 
-        assignments = []
+        statements = []
 
         # Employ existing names to access the sequence.
         # Literal sequences do not provide names of accessible objects.
@@ -447,19 +447,25 @@
             temp = self.get_temporary_name()
             self.next_temporary()
 
-            assignments.append(
+            statements.append(
                 compiler.ast.Assign([compiler.ast.AssName(temp, "OP_ASSIGN")], expr)
                 )
 
+        # Generate a test for the length of the expression object.
+
+        statements.append(compiler.ast.Discard(
+            compiler.ast.CallFunc(compiler.ast.Name("$seq_test_length"),
+                [compiler.ast.Name(temp), compiler.ast.Const(len(n.nodes))])))
+
         # Assign the items to the target nodes.
 
         for i, node in enumerate(n.nodes):
-            assignments.append(
+            statements.append(
                 compiler.ast.Assign([node], compiler.ast.Subscript(
                     compiler.ast.Name(temp), "OP_APPLY", [compiler.ast.Const(i, str(i))]))
                 )
 
-        return self.process_structure_node(compiler.ast.Stmt(assignments))
+        return self.process_structure_node(compiler.ast.Stmt(statements))
 
     def process_literal_sequence_items(self, n, name_ref):
 
diff -r 1b1c1664e774 -r 4bf5180fbfee inspector.py
--- a/inspector.py	Mon Jul 02 17:53:15 2018 +0200
+++ b/inspector.py	Mon Jul 02 19:19:54 2018 +0200
@@ -873,6 +873,15 @@
             self.set_special(n.name, value)
             return value
 
+        # Special case for sequence length testing.
+
+        elif n.name.startswith("$seq"):
+            op = n.name[len("$seq"):]
+            ref = self.import_name_from_module(op, "__builtins__.sequence")
+            value = ResolvedNameRef(n.name, ref)
+            self.set_special(n.name, value)
+            return value
+
         # Special case for print operations.
 
         elif n.name.startswith("$print"):
diff -r 1b1c1664e774 -r 4bf5180fbfee lib/__builtins__/sequence.py
--- a/lib/__builtins__/sequence.py	Mon Jul 02 17:53:15 2018 +0200
+++ b/lib/__builtins__/sequence.py	Mon Jul 02 19:19:54 2018 +0200
@@ -3,7 +3,7 @@
 """
 Sequence operations.
 
-Copyright (C) 2015, 2016, 2017 Paul Boddie <paul@boddie.org.uk>
+Copyright (C) 2015, 2016, 2017, 2018 Paul Boddie <paul@boddie.org.uk>
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -267,4 +267,11 @@
     else:
         return index
 
+def _test_length(seq, length):
+
+    "Helper function for asserting that 'seq' is of the given 'length'."
+
+    if len(seq) != length:
+        raise ValueError, length
+
 # vim: tabstop=4 expandtab shiftwidth=4
diff -r 1b1c1664e774 -r 4bf5180fbfee tests/tuple.py
--- a/tests/tuple.py	Mon Jul 02 17:53:15 2018 +0200
+++ b/tests/tuple.py	Mon Jul 02 19:19:54 2018 +0200
@@ -23,3 +23,11 @@
     print t[-5]         # should raise an exception
 except IndexError, exc:
     print "t[-5]: failed with argument", exc.index
+
+a, b, c, d = l
+print a, b, c, d        # 1 2 3 "four"
+
+try:
+    a, b, c = l
+except ValueError, exc:
+    print "a, b, c = l: failed with length", exc.value
diff -r 1b1c1664e774 -r 4bf5180fbfee translator.py
--- a/translator.py	Mon Jul 02 17:53:15 2018 +0200
+++ b/translator.py	Mon Jul 02 19:19:54 2018 +0200
@@ -1564,7 +1564,7 @@
         # function names to references.
 
         elif n.name.startswith("$L") or n.name.startswith("$op") or \
-             n.name.startswith("$print"):
+             n.name.startswith("$seq") or n.name.startswith("$print"):
 
             ref, paths = self.importer.get_module(self.name).special[n.name]
             return TrResolvedNameRef(n.name, ref)