Add the print function built-in,

Fixes wala#93.

com.ibm.wala.cast.python.test/data/print.py

@@ -0,0 +1,6 @@
+# From https://github.com/wala/ML/issues/93#issue-1953025479.
+def f(x):
+  print("Traced with: " + str(x))
+
+
+f(1)

com.ibm.wala.cast.python.test/source/com/ibm/wala/cast/python/test/TestPrint.java

@@ -0,0 +1,101 @@
+package com.ibm.wala.cast.python.test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import com.ibm.wala.cast.ir.ssa.AstLexicalAccess.Access;
+import com.ibm.wala.cast.ir.ssa.AstLexicalRead;
+import com.ibm.wala.cast.python.client.PythonAnalysisEngine;
+import com.ibm.wala.cast.python.ssa.PythonInvokeInstruction;
+import com.ibm.wala.cast.python.types.PythonTypes;
+import com.ibm.wala.classLoader.IClass;
+import com.ibm.wala.ipa.callgraph.CGNode;
+import com.ibm.wala.ipa.callgraph.CallGraph;
+import com.ibm.wala.ipa.callgraph.propagation.InstanceKey;
+import com.ibm.wala.ipa.callgraph.propagation.PointerKey;
+import com.ibm.wala.ipa.callgraph.propagation.SSAPropagationCallGraphBuilder;
+import com.ibm.wala.ipa.cha.ClassHierarchyException;
+import com.ibm.wala.ssa.IR;
+import com.ibm.wala.ssa.SSAInstruction;
+import com.ibm.wala.types.TypeReference;
+import com.ibm.wala.util.CancelException;
+import com.ibm.wala.util.intset.OrdinalSet;
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Iterator;
+import org.junit.Test;
+
+public class TestPrint extends TestPythonCallGraphShape {
+
+  private static final String PRINT_FUNCTION_VARIABLE_NAME = "print";
+
+  private static final TypeReference PRINT_FUNCTION_TYPE_REFERENCE =
+      TypeReference.findOrCreate(
+          PythonTypes.pythonLoader, "Lwala/builtin/" + PRINT_FUNCTION_VARIABLE_NAME);
+
+  @Test
+  public void testPrint()
+      throws ClassHierarchyException, IllegalArgumentException, CancelException, IOException {
+    PythonAnalysisEngine<?> engine = makeEngine("print.py");
+    SSAPropagationCallGraphBuilder builder =
+        (SSAPropagationCallGraphBuilder) engine.defaultCallGraphBuilder();
+    CallGraph CG = builder.makeCallGraph(builder.getOptions());
+
+    Collection<CGNode> nodes = getNodes(CG, "script print.py/f");
+    assertEquals(1, nodes.size());
+
+    assertTrue(nodes.iterator().hasNext());
+    CGNode fNode = nodes.iterator().next();
+
+    IR fIR = fNode.getIR();
+
+    boolean foundPrintCall = false;
+    boolean foundBuiltIn = false;
+
+    for (Iterator<SSAInstruction> iit = fIR.iterateNormalInstructions(); iit.hasNext(); ) {
+      SSAInstruction instruction = iit.next();
+
+      if (instruction instanceof PythonInvokeInstruction) {
+        PythonInvokeInstruction invokeInstruction = (PythonInvokeInstruction) instruction;
+        int receiver = invokeInstruction.getReceiver();
+        assertTrue(receiver >= 0);
+
+        SSAInstruction receiverDefinition = fNode.getDU().getDef(receiver);
+
+        if (receiverDefinition instanceof AstLexicalRead) {
+          AstLexicalRead read = (AstLexicalRead) receiverDefinition;
+
+          assertEquals(1, read.getAccessCount());
+          Access access = read.getAccess(0);
+
+          if (access.variableName.equals(PRINT_FUNCTION_VARIABLE_NAME)) {
+            foundPrintCall = true;
+
+            // Found the print call. Let's ensure that it "points" to the built-in function.
+            PointerKey pk =
+                builder
+                    .getPointerAnalysis()
+                    .getHeapModel()
+                    .getPointerKeyForLocal(fNode, access.valueNumber);
+            OrdinalSet<InstanceKey> pointsToSet = builder.getPointerAnalysis().getPointsToSet(pk);
+
+            for (Iterator<InstanceKey> pit = pointsToSet.iterator(); pit.hasNext(); ) {
+              InstanceKey ik = pit.next();
+
+              IClass concreteType = ik.getConcreteType();
+              TypeReference typeReference = concreteType.getReference();
+
+              if (typeReference.equals(PRINT_FUNCTION_TYPE_REFERENCE)) {
+                // found the built-in function in the pointer analysis.
+                foundBuiltIn = true;
+                break;
+              }
+            }
+          }
+        }
+      }
+    }
+
+    assertTrue(foundPrintCall && foundBuiltIn);
+  }
+}

com.ibm.wala.cast.python/source/com/ibm/wala/cast/python/ipa/summaries/BuiltinFunctions.java

@@ -286,6 +286,8 @@ private static TypeReference builtinFunction(String name) {
     builtinFunctions.put("zip", Either.forLeft(PythonTypes.list));
     builtinFunctions.put("slice", Either.forRight(2));
     builtinFunctions.put("__delete__", Either.forRight(2));
+    // https://docs.python.org/3/library/functions.html#print
+    builtinFunctions.put("print", Either.forLeft(TypeReference.Void));
   }
 
   public static Set<String> builtins() {