Model implicit reads of self variables

We already synthesise `self` nodes for method calls with no receiver.
This change creates read accesses for each of these synthesised nodes.

ruby/ql/lib/codeql/ruby/ast/Variable.qll

@@ -193,3 +193,6 @@ class ClassVariableReadAccess extends ClassVariableAccess, VariableReadAccess {
 class SelfVariableAccess extends VariableAccess instanceof SelfVariableAccessImpl {
   final override string getAPrimaryQlClass() { result = "SelfVariableAccess" }
 }
+
+/** An access to the `self` variable where the value is read. */
+class SelfVariableReadAccess extends SelfVariableAccess, VariableReadAccess { }

ruby/ql/lib/codeql/ruby/ast/internal/AST.qll

@@ -236,8 +236,9 @@ private module Cached {
       isScopeResolutionMethodCall(g, i)
     } or
     TSelfReal(Ruby::Self g) or
-    TSelfSynth(AST::AstNode parent, int i) { mkSynthChild(SelfKind(), parent, i) } or
-    TSelfVariableAccessReal(Ruby::Self self, MethodBase::Range scope) { scopeOf(self) = scope } or
+    TSelfSynth(AST::AstNode parent, int i, AST::SelfVariable v) {
+      mkSynthChild(SelfKind(v), parent, i)
+    } or
     TSimpleParameter(Ruby::Identifier g) { g instanceof Parameter::Range } or
     TSimpleSymbolLiteral(Ruby::SimpleSymbol g) or
     TSingletonClass(Ruby::SingletonClass g) or
@@ -478,7 +479,7 @@ private module Cached {
     or
     result = TRShiftExprSynth(parent, i)
     or
-    result = TSelfSynth(parent, i)
+    result = TSelfSynth(parent, i, _)
     or
     result = TSplatExprSynth(parent, i)
     or
@@ -706,4 +707,4 @@ class TInstanceVariableAccess = TInstanceVariableAccessReal or TInstanceVariable
 
 class TClassVariableAccess = TClassVariableAccessReal or TClassVariableAccessSynth;
 
-class TSelfVariableAccess = TSelfVariableAccessReal;
+class TSelfVariableAccess = TSelfReal or TSelfSynth;

ruby/ql/lib/codeql/ruby/ast/internal/Call.qll

@@ -60,7 +60,7 @@ class IdentifierMethodCall extends MethodCallImpl, TIdentifierMethodCall {
 
   final override string getMethodNameImpl() { result = g.getValue() }
 
-  final override AstNode getReceiverImpl() { result = TSelfSynth(this, 0) }
+  final override AstNode getReceiverImpl() { result = TSelfSynth(this, 0, _) }
 
   final override Expr getArgumentImpl(int n) { none() }
 
@@ -97,7 +97,7 @@ class RegularMethodCall extends MethodCallImpl, TRegularMethodCall {
     not exists(g.getReceiver()) and
     toGenerated(result) = g.getMethod().(Ruby::ScopeResolution).getScope()
     or
-    result = TSelfSynth(this, 0)
+    result = TSelfSynth(this, 0, _)
   }
 
   final override string getMethodNameImpl() {

ruby/ql/lib/codeql/ruby/ast/internal/Synthesis.qll

@@ -5,6 +5,7 @@ private import TreeSitter
 private import codeql.ruby.ast.internal.Call
 private import codeql.ruby.ast.internal.Variable
 private import codeql.ruby.ast.internal.Pattern
+private import codeql.ruby.ast.internal.Scope
 private import codeql.ruby.AST
 
 /** A synthesized AST node kind. */
@@ -34,7 +35,7 @@ newtype SynthKind =
   RShiftExprKind() or
   SplatExprKind() or
   StmtSequenceKind() or
-  SelfKind() or
+  SelfKind(SelfVariable v) or
   SubExprKind() or
   ConstantReadAccessKind(string value) { any(Synthesis s).constantReadAccess(value) }
 
@@ -142,7 +143,7 @@ private predicate hasLocation(AstNode n, Location l) {
 private module ImplicitSelfSynthesis {
   pragma[nomagic]
   private predicate identifierMethodCallSelfSynthesis(AstNode mc, int i, Child child) {
-    child = SynthChild(SelfKind()) and
+    child = SynthChild(SelfKind(TSelfVariable(scopeOf(toGenerated(mc))))) and
     mc = TIdentifierMethodCall(_) and
     i = 0
   }
@@ -163,7 +164,7 @@ private module ImplicitSelfSynthesis {
       not exists(g.(Ruby::Call).getReceiver()) and
       not exists(g.(Ruby::Call).getMethod().(Ruby::ScopeResolution).getScope())
     ) and
-    child = SynthChild(SelfKind()) and
+    child = SynthChild(SelfKind(TSelfVariable(scopeOf(toGenerated(mc))))) and
     i = 0
   }
 

ruby/ql/lib/codeql/ruby/ast/internal/Variable.qll

@@ -308,7 +308,8 @@ private module Cached {
       access(this, _) or
       this instanceof Ruby::GlobalVariable or
       this instanceof Ruby::InstanceVariable or
-      this instanceof Ruby::ClassVariable
+      this instanceof Ruby::ClassVariable or
+      this instanceof Ruby::Self
     }
   }
 
@@ -619,15 +620,23 @@ private class ClassVariableAccessSynth extends ClassVariableAccessRealImpl,
 
 abstract class SelfVariableAccessImpl extends VariableAccessImpl, TSelfVariableAccess { }
 
-private class SelfVariableAccessReal extends SelfVariableAccessImpl, TSelfVariableAccessReal {
+private class SelfVariableAccessReal extends SelfVariableAccessImpl, TSelfReal {
   private Ruby::Self self;
   private SelfVariable var;
 
-  SelfVariableAccessReal() {
-    exists(MethodBase::Range scope |
-      var = TSelfVariable(scope) and this = TSelfVariableAccessReal(self, scope)
-    )
-  }
+  SelfVariableAccessReal() { this = TSelfReal(self) and var = TSelfVariable(scopeOf(self)) }
 
   final override SelfVariable getVariableImpl() { result = var }
+
+  final override string toString() { result = var.toString() }
+}
+
+private class SelfVariableAccessSynth extends SelfVariableAccessImpl, TSelfSynth {
+  private SelfVariable v;
+
+  SelfVariableAccessSynth() { this = TSelfSynth(_, _, v) }
+
+  final override LocalVariable getVariableImpl() { result = v }
+
+  final override string toString() { result = v.getName() }
 }