Infer string interpolation with ``%``

[pylint-bot]

Originally reported by: Claudiu Popa (BitBucket: PCManticore, GitHub: @PCManticore)

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Not sure how important this is, but we could understand string interpolation, both msg % something, as well as msg.format(something). Currently, for the second form we are returning an empty string, which is wrong, while the first form we're returning an YES object.

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• Bitbucket: https://bitbucket.org/logilab/astroid/issue/151

[DanielNoord]

Let's merge #1602 first and rescope this to inference of msg % something.

I have a WIP diff for this PR that fixes the most simple cases:

diff --git a/astroid/inference.py b/astroid/inference.py
index 61b46e10d..cd0108c87 100644
--- a/astroid/inference.py
+++ b/astroid/inference.py
@@ -562,12 +562,24 @@ def _is_not_implemented(const):
     return isinstance(const, nodes.Const) and const.value is NotImplemented
 
 
-def _invoke_binop_inference(instance, opnode, op, other, context, method_name):
+def _invoke_binop_inference(
+    instance, opnode, op, other, context: InferenceContext, method_name
+):
     """Invoke binary operation inference on the given instance."""
     methods = dunder_lookup.lookup(instance, method_name)
     context = bind_context_to_node(context, instance)
     method = methods[0]
     context.callcontext.callee = method
+
+    if isinstance(instance, nodes.Const) and op == "%":
+        if isinstance(other, nodes.Tuple):
+            inferred_positional = [helpers.safe_infer(i, context) for i in other.elts]
+            if all(isinstance(i, nodes.Const) for i in inferred_positional):
+                values_positional = [i.value for i in inferred_positional]
+                return iter(
+                    [nodes.const_factory(instance.value % tuple(values_positional))]
+                )
+
     try:
         inferred = next(method.infer(context=context))
     except StopIteration as e: