C#: Reinstate toString for SSA data flow nodes.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/dataflow/SSA.qll

@@ -516,8 +516,6 @@ module Ssa {
     }
 
     override Element getElement() { result = ad.getElement() }
-
-    override string toString() { result = "SSA def(" + this.getSourceVariable() + ")" }
   }
 
   /**
@@ -561,12 +559,6 @@ module Ssa {
     final Callable getCallable() { result = this.getBasicBlock().getEnclosingCallable() }
 
     override Element getElement() { result = this.getCallable() }
-
-    override string toString() {
-      if this.getSourceVariable().getAssignable() instanceof LocalScopeVariable
-      then result = "SSA capture def(" + this.getSourceVariable() + ")"
-      else result = "SSA entry def(" + this.getSourceVariable() + ")"
-    }
   }
 
   pragma[nomagic]
@@ -597,10 +589,6 @@ module Ssa {
     Parameter getParameter() { result = p }
 
     override Element getElement() { result = this.getParameter() }
-
-    override string toString() {
-      result = "SSA param(" + pragma[only_bind_out](this.getParameter()) + ")"
-    }
   }
 
   /**
@@ -694,8 +682,6 @@ module Ssa {
     predicate hasInputFromBlock(Definition inp, BasicBlock bb) {
       inp = SsaImpl::phiHasInputFromBlock(this, bb)
     }
-
-    override string toString() { result = "SSA phi(" + this.getSourceVariable() + ")" }
   }
 
   /**

csharp/ql/lib/semmle/code/csharp/dataflow/internal/SsaImpl.qll

@@ -77,6 +77,10 @@ module Ssa_ = Impl::MakeSsa<SsaInput>;
 
 class Definition = Impl::Definition;
 
+private class SsaDefinitionToStringProxy extends Definition {
+  override string toString() { result = this.(SsaDefinition).toString() }
+}
+
 deprecated class WriteDefinition = Impl::WriteDefinition;
 
 deprecated class UncertainWriteDefinition = Impl::UncertainWriteDefinition;

shared/ssa/codeql/ssa/Ssa.qll

@@ -1054,7 +1054,7 @@ module Make<
     /** A static single assignment (SSA) definition. */
     class SsaDefinition extends FinalDefinition {
       /** Gets a textual representation of this SSA definition. */
-      string toString() { result = super.toString() }
+      string toString() { result = "SSA def(" + this.getSourceVariable() + ")" }
 
       /**
        * Gets the control flow node of this SSA definition.
@@ -1207,6 +1207,8 @@ module Make<
      * a phi definition for `x` is inserted just before the call `puts x`.
      */
     class SsaPhiDefinition extends SsaDefinition instanceof PhiNode {
+      override string toString() { result = "SSA phi(" + this.getSourceVariable() + ")" }
+
       /** Holds if `inp` is an input to this phi definition along the edge originating in `bb`. */
       predicate hasInputFromBlock(SsaDefinition inp, BasicBlock bb) {
         phiHasInputFromBlockCached(this, inp, bb)