Extend the scope of self variables

`self` variables are scoped to methods, modules, classes and the
top-level of the program. Prior to this change, they were treated as
being scoped just to methods.

This change means we (once again) correctly synthesise `self` receivers
for method calls in class bodies, module bodies and at the top-level.

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

@@ -20,3 +20,5 @@ class Scope extends AstNode, TScopeType {
     result.getName() = name
   }
 }
+
+class SelfScope extends Scope, TSelfScopeType { }

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

@@ -72,10 +72,7 @@ class ClassVariable extends Variable instanceof ClassVariableImpl {
 }
 
 /** A `self` variable. */
-class SelfVariable extends LocalVariable instanceof SelfVariableImpl {
-  /** Gets the method that this `self` variable belongs to. */
-  MethodBase getMethod() { result = this.getDeclaringScope() }
-}
+class SelfVariable extends LocalVariable instanceof SelfVariableImpl { }
 
 /** An access to a variable. */
 class VariableAccess extends Expr instanceof VariableAccessImpl {

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

@@ -5,6 +5,12 @@ private import codeql.ruby.ast.internal.Parameter
 
 class TScopeType = TMethodBase or TModuleLike or TBlockLike;
 
+/**
+ * The scope of a `self` variable.
+ * This differs from a normal scope because it is not affected by blocks or lambdas.
+ */
+class TSelfScopeType = TMethodBase or TModuleBase;
+
 private class TBlockLike = TDoBlock or TLambda or TBlock or TEndBlock;
 
 private class TModuleLike = TToplevel or TModuleDeclaration or TClassDeclaration or TSingletonClass;
@@ -29,6 +35,12 @@ module Scope {
       result = this.getOuterScope().getEnclosingMethod()
     }
 
+    SelfBase::Range getEnclosingSelfScope() {
+      this instanceof SelfBase::Range and result = this
+      or
+      not this instanceof SelfBase::Range and result = this.getOuterScope().getEnclosingSelfScope()
+    }
+
     Range getOuterScope() { result = scopeOf(this) }
   }
 }
@@ -59,6 +71,15 @@ module ModuleBase {
   class Range extends Scope::Range, TypeRange { }
 }
 
+module SelfBase {
+  class TypeRange = MethodBase::TypeRange or ModuleBase::TypeRange;
+
+  /**
+   * A `self` variable can appear in a class, module, method or at the top level.
+   */
+  class Range extends Scope::Range, TypeRange { }
+}
+
 pragma[noinline]
 private predicate rankHeredocBody(File f, Ruby::HeredocBody b, int i) {
   b =

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

@@ -143,7 +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(TSelfVariable(scopeOf(toGenerated(mc))))) and
+    child = SynthChild(SelfKind(TSelfVariable(scopeOf(toGenerated(mc)).getEnclosingSelfScope()))) and
     mc = TIdentifierMethodCall(_) and
     i = 0
   }
@@ -164,7 +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(TSelfVariable(scopeOf(toGenerated(mc))))) and
+    child = SynthChild(SelfKind(TSelfVariable(scopeOf(toGenerated(mc)).getEnclosingSelfScope()))) and
     i = 0
   }
 

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

@@ -133,7 +133,7 @@ private module Cached {
       not scopeDefinesParameterVariable(scope, name, _) and
       not inherits(scope, name, _)
     } or
-    TSelfVariable(MethodBase::Range scope) or
+    TSelfVariable(SelfBase::Range scope) or
     TLocalVariableSynth(AstNode n, int i) { any(Synthesis s).localVariable(n, i) }
 
   // Db types that can be vcalls
@@ -479,7 +479,7 @@ class ClassVariableImpl extends VariableReal, TClassVariable {
 }
 
 class SelfVariableImpl extends VariableReal, TSelfVariable {
-  private MethodBase::Range scope;
+  private SelfBase::Range scope;
 
   SelfVariableImpl() { this = TSelfVariable(scope) }
 

ruby/ql/lib/codeql/ruby/dataflow/SSA.qll

@@ -228,7 +228,7 @@ module Ssa {
 
     SelfDefinition() { this.definesAt(v, _, _) }
 
-    final override string toString() { result = "self (" + v.getMethod() + ")" }
+    final override string toString() { result = "self (" + v.getDeclaringScope() + ")" }
 
     final override Location getLocation() { result = this.getControlFlowNode().getLocation() }
   }