Merge pull request #108 from github/hvitved/ssa

Add SSA library

ql/src/codeql_ruby/ast/Expr.qll

@@ -1,5 +1,8 @@
 private import codeql_ruby.AST
+private import codeql_ruby.CFG
 private import internal.Expr
+private import internal.Variable
+private import codeql_ruby.controlflow.internal.ControlFlowGraphImpl
 
 /**
  * An expression.
@@ -10,6 +13,18 @@ class Expr extends AstNode {
   Expr::Range range;
 
   Expr() { this = range }
+
+  /** Gets a control-flow node for this expression, if any. */
+  CfgNodes::AstCfgNode getAControlFlowNode() { result.getNode() = this }
+
+  /** Gets the control-flow scope of this expression, if any. */
+  CfgScope getCfgScope() { result = getCfgScope(this) }
+
+  /** Gets the variable scope that this expression belongs to. */
+  VariableScope getVariableScope() { result = enclosingScope(this) }
+
+  /** Gets the enclosing callable, if any. */
+  Callable getEnclosingCallable() { result = this.getCfgScope() }
 }
 
 /**

ql/src/codeql_ruby/ast/Method.qll

@@ -1,9 +1,10 @@
 private import codeql_ruby.AST
+private import codeql_ruby.controlflow.ControlFlowGraph
 private import internal.TreeSitter
 private import internal.Method
 
 /** A callable. */
-class Callable extends AstNode {
+class Callable extends AstNode, CfgScope {
   Callable::Range range;
 
   Callable() { range = this }

ql/src/codeql_ruby/ast/Parameter.qll

@@ -22,10 +22,10 @@ class Parameter extends AstNode {
   final int getPosition() { result = pos }
 
   /** Gets a variable introduced by this parameter. */
-  Variable getAVariable() { none() }
+  LocalVariable getAVariable() { none() }
 
   /** Gets the variable named `name` introduced by this parameter. */
-  final Variable getVariable(string name) {
+  final LocalVariable getVariable(string name) {
     result = this.getAVariable() and
     result.getName() = name
   }
@@ -37,7 +37,7 @@ class Parameter extends AstNode {
  * This includes both simple parameters and tuple parameters.
  */
 class PatternParameter extends Parameter, Pattern {
-  override Variable getAVariable() { result = Pattern.super.getAVariable() }
+  override LocalVariable getAVariable() { result = Pattern.super.getAVariable() }
 }
 
 /** A parameter defined using a tuple pattern. */
@@ -53,9 +53,9 @@ class NamedParameter extends Parameter {
   string getName() { none() }
 
   /** Gets the variable introduced by this parameter. */
-  Variable getVariable() { none() }
+  LocalVariable getVariable() { none() }
 
-  override Variable getAVariable() { result = this.getVariable() }
+  override LocalVariable getAVariable() { result = this.getVariable() }
 
   /** Gets an access to this parameter. */
   final VariableAccess getAnAccess() { result = this.getVariable().getAnAccess() }
@@ -65,9 +65,9 @@ class NamedParameter extends Parameter {
 class SimpleParameter extends NamedParameter, PatternParameter, VariablePattern {
   final override string getName() { result = range.getVariableName() }
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, this) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, this) }
 
-  final override Variable getAVariable() { result = this.getVariable() }
+  final override LocalVariable getAVariable() { result = this.getVariable() }
 
   final override string getAPrimaryQlClass() { result = "SimpleParameter" }
 
@@ -85,7 +85,7 @@ class SimpleParameter extends NamedParameter, PatternParameter, VariablePattern
 class BlockParameter extends @block_parameter, NamedParameter {
   final override Generated::BlockParameter generated;
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
 
   final override string getAPrimaryQlClass() { result = "BlockParameter" }
 
@@ -106,7 +106,7 @@ class BlockParameter extends @block_parameter, NamedParameter {
 class HashSplatParameter extends @hash_splat_parameter, NamedParameter {
   final override Generated::HashSplatParameter generated;
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
 
   final override string getAPrimaryQlClass() { result = "HashSplatParameter" }
 
@@ -129,7 +129,7 @@ class HashSplatParameter extends @hash_splat_parameter, NamedParameter {
 class KeywordParameter extends @keyword_parameter, NamedParameter {
   final override Generated::KeywordParameter generated;
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
 
   final override string getAPrimaryQlClass() { result = "KeywordParameter" }
 
@@ -164,7 +164,7 @@ class KeywordParameter extends @keyword_parameter, NamedParameter {
 class OptionalParameter extends @optional_parameter, NamedParameter {
   final override Generated::OptionalParameter generated;
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
 
   final override string getAPrimaryQlClass() { result = "OptionalParameter" }
 
@@ -191,7 +191,7 @@ class OptionalParameter extends @optional_parameter, NamedParameter {
 class SplatParameter extends @splat_parameter, NamedParameter {
   final override Generated::SplatParameter generated;
 
-  final override Variable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
+  final override LocalVariable getVariable() { result = TLocalVariable(_, _, generated.getName()) }
 
   final override string getAPrimaryQlClass() { result = "SplatParameter" }
 

ql/src/codeql_ruby/ast/Variable.qll

@@ -57,6 +57,25 @@ class LocalVariable extends Variable, TLocalVariable {
   override LocalVariable::Range range;
 
   final override LocalVariableAccess getAnAccess() { result.getVariable() = this }
+
+  /** Gets the access where this local variable is first introduced. */
+  VariableAccess getDefiningAccess() { result = range.getDefiningAccess() }
+
+  /**
+   * Holds if this variable is captured. For example in
+   *
+   * ```rb
+   * def m x
+   *   x.times do |y|
+   *     puts x
+   *   end
+   *   puts x
+   * end
+   * ```
+   *
+   * `x` is a captured variable, whereas `y` is not.
+   */
+  predicate isCaptured() { this.getAnAccess().isCapturedAccess() }
 }
 
 /** A global variable. */
@@ -133,6 +152,23 @@ class LocalVariableAccess extends VariableAccess, @token_identifier {
   final override string getAPrimaryQlClass() {
     not this instanceof SimpleParameter and result = "LocalVariableAccess"
   }
+
+  /**
+   * Holds if this access is a captured variable access. For example in
+   *
+   * ```rb
+   * def m x
+   *   x.times do |y|
+   *     puts x
+   *   end
+   *   puts x
+   * end
+   * ```
+   *
+   * the access to `x` in the first `puts x` is a captured access, while
+   * the access to `x` in the second `puts x` is not.
+   */
+  final predicate isCapturedAccess() { isCapturedAccess(this) }
 }
 
 /** An access to a local variable where the value is updated. */

ql/src/codeql_ruby/ast/internal/Pattern.qll

@@ -39,6 +39,7 @@ predicate implicitParameterAssignmentNode(Generated::AstNode n, Callable c) {
 
 module Pattern {
   abstract class Range extends AstNode {
+    cached
     Range() {
       explicitAssignmentNode(this, _)
       or

ql/src/codeql_ruby/ast/internal/Variable.qll

@@ -9,11 +9,6 @@ private Generated::AstNode parent(Generated::AstNode n) {
   not n = any(VariableScope s).getScopeElement()
 }
 
-/** Gets the enclosing scope for `node`. */
-private VariableScope enclosingScope(Generated::AstNode node) {
-  result.getScopeElement() = parent*(node.getParent())
-}
-
 private predicate parameterAssignment(
   CallableScope::Range scope, string name, Generated::Identifier i
 ) {
@@ -98,6 +93,12 @@ private class CapturingScope extends VariableScope {
 
 cached
 private module Cached {
+  /** Gets the enclosing scope for `node`. */
+  cached
+  VariableScope enclosingScope(Generated::AstNode node) {
+    result.getScopeElement() = parent*(node.getParent())
+  }
+
   cached
   newtype TScope =
     TGlobalScope() or
@@ -301,6 +302,11 @@ private module Cached {
     or
     scopeDefinesParameterVariable(_, _, access)
   }
+
+  cached
+  predicate isCapturedAccess(LocalVariableAccess::Range access) {
+    access.getVariable().getDeclaringScope() != enclosingScope(access)
+  }
 }
 
 import Cached
@@ -391,6 +397,8 @@ module LocalVariable {
     final override Location getLocation() { result = i.getLocation() }
 
     final override VariableScope getDeclaringScope() { result = scope }
+
+    final VariableAccess getDefiningAccess() { result = i }
   }
 }