Check for compile-time constants in DartCompiler

compiler/java/com/google/dart/compiler/resolver/CompileTimeConstVisitor.java

+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+package com.google.dart.compiler.resolver;
+
+import com.google.dart.compiler.DartCompilerErrorCode;
+import com.google.dart.compiler.InternalCompilerException;
+import com.google.dart.compiler.ast.DartArrayLiteral;
+import com.google.dart.compiler.ast.DartBinaryExpression;
+import com.google.dart.compiler.ast.DartExpression;
+import com.google.dart.compiler.ast.DartFunction;
+import com.google.dart.compiler.ast.DartFunctionObjectInvocation;
+import com.google.dart.compiler.ast.DartIdentifier;
+import com.google.dart.compiler.ast.DartInvocation;
+import com.google.dart.compiler.ast.DartMapLiteral;
+import com.google.dart.compiler.ast.DartMethodInvocation;
+import com.google.dart.compiler.ast.DartNewExpression;
+import com.google.dart.compiler.ast.DartNode;
+import com.google.dart.compiler.ast.DartNodeTraverser;
+import com.google.dart.compiler.ast.DartParenthesizedExpression;
+import com.google.dart.compiler.ast.DartPropertyAccess;
+import com.google.dart.compiler.ast.DartRedirectConstructorInvocation;
+import com.google.dart.compiler.ast.DartStringInterpolation;
+import com.google.dart.compiler.ast.DartSuperExpression;
+import com.google.dart.compiler.ast.DartThisExpression;
+import com.google.dart.compiler.ast.DartUnaryExpression;
+import com.google.dart.compiler.ast.DartUnqualifiedInvocation;
+import com.google.dart.compiler.type.Type;
+
+/**
+ * Given an expression, Determines if the expression matches all the rules for a
+ * compile-time constant expression and emits a resolution error if not.
+ *
+ * This script doesn't just resolve expressions, it also sets types to the
+ * extent needed to validate compile-time constant expressions (boolean, int,
+ * double, and string types might be set)
+ *
+ */
+public class CompileTimeConstVisitor extends DartNodeTraverser<Void> {
+
+  static CompileTimeConstVisitor create(CoreTypeProvider typeProvider, ResolutionContext context) {
+    return new CompileTimeConstVisitor(typeProvider, context);
+  }
+
+  private final ResolutionContext context;
+
+  private final Type boolType;
+  private final Type doubleType;
+  private final Type intType;
+  private final Type numType;
+  private final Type stringType;
+  private final Type dynamicType;
+
+
+  private CompileTimeConstVisitor(CoreTypeProvider typeProvider, ResolutionContext context) {
+    this.context = context;
+    this.boolType = typeProvider.getBoolType();
+    this.doubleType = typeProvider.getDoubleType();
+    this.intType = typeProvider.getIntType();
+    this.numType = typeProvider.getNumType();
+    this.stringType = typeProvider.getStringType();
+    this.dynamicType = typeProvider.getDynamicType();
+  }
+
+  private boolean checkBoolean(DartNode x, Type type) {
+    if (!type.equals(boolType)) {
+      context.resolutionError(x, DartCompilerErrorCode.EXPECTED_CONSTANT_EXPRESSION_BOOLEAN,
+                              type.toString());
+      return false;
+    }
+    return true;
+  }
+
+  private boolean checkInt(DartNode x, Type type) {
+    if (!type.equals(intType)) {
+      context.resolutionError(x, DartCompilerErrorCode.EXPECTED_CONSTANT_EXPRESSION_INT,
+                              type.toString());
+      return false;
+    }
+    return true;
+  }
+
+  private boolean checkNumber(DartNode x, Type type) {
+    if (!(type.equals(numType) || type.equals(intType) || type.equals(doubleType))) {
+      context.resolutionError(x, DartCompilerErrorCode.EXPECTED_CONSTANT_EXPRESSION_NUMBER,
+                              type.toString());
+      return false;
+    }
+    return true;
+  }
+
+  private boolean checkNumberBooleanOrStringType(DartNode x, Type type) {
+    if (!type.equals(intType) && !type.equals(boolType)
+        && !type.equals(numType) && !type.equals(doubleType) && !type.equals(stringType)) {
+      context.resolutionError(x,
+          DartCompilerErrorCode.EXPECTED_CONSTANT_EXPRESSION_STRING_NUMBER_BOOL,
+          type.toString());
+      return false;
+    }
+    return true;
+  }
+
+  @Override
+  public Void visitBinaryExpression(DartBinaryExpression x) {
+    x.visitChildren(this);
+
+    DartExpression lhs = x.getArg1();
+    DartExpression rhs = x.getArg2();
+    Type lhsType = getMostSpecificType(lhs);
+    Type rhsType = getMostSpecificType(rhs);
+    lhsType.getClass(); // fast null check
+    rhsType.getClass(); // fast null check
+    switch (x.getOperator()) {
+      case NE:
+      case EQ:
+      case NE_STRICT:
+      case EQ_STRICT:
+        if (checkNumberBooleanOrStringType(lhs, lhsType)
+            && checkNumberBooleanOrStringType(rhs, rhsType)) {
+          setType(x, boolType);
+        }
+        break;
+
+      case AND:
+      case OR:
+        if (checkBoolean(lhs, lhsType) && checkBoolean(rhs, rhsType)) {
+          setType(x, boolType);
+        }
+        break;
+
+      case BIT_NOT:
+      case TRUNC:
+      case BIT_XOR:
+      case BIT_AND:
+      case BIT_OR:
+      case SAR:
+      case SHL:
+        if (checkInt(lhs, lhsType) && checkInt(rhs, rhsType)) {
+          setType(x, intType);
+        }
+        break;
+
+      case ADD:
+      case SUB:
+      case MUL:
+      case DIV:
+      case MOD:
+        if (checkNumber(lhs, lhsType) && checkNumber(rhs, rhsType)) {
+          setType(x, numType);
+        }
+        break;
+      case LT:
+      case GT:
+      case LTE:
+      case GTE:
+        if (checkNumber(lhs, lhsType) && checkNumber(rhs, rhsType)) {
+          setType(x, boolType);
+        }
+        break;
+
+      default:
+        // all other operators...
+        expectedConstant(x);
+    }
+    return null;
+  }
+
+  @Override
+  public Void visitParenthesizedExpression(DartParenthesizedExpression x) {
+    x.visitChildren(this);
+    Type type = getMostSpecificType(x.getExpression());
+    setType(x, type);
+    return null;
+  }
+
+  @Override
+  public Void visitPropertyAccess(DartPropertyAccess x) {
+    x.visitChildren(this);

[ngeoffray, 2011/10/17 10:59:38]

Do you really need to visit children here?

[zundel, 2011/10/17 14:14:26]

a qualifier is a part of a PropertyAccess and is typed a  DartExpression.  I
assume it could be a constant or non-constant expression.

+    switch (ElementKind.of(x.getQualifier().getSymbol())) {
+      case CLASS:
+      case LIBRARY:
+      case NONE:
+        // OK.
+        break;
+      default:
+        expectedConstant(x);
+        return null;
+    }
+    Element element = x.getName().getSymbol();
+    if (element != null && !element.getModifiers().isConstant()) {
+      expectedConstant(x);
+    }
+    Type type = getMostSpecificType(x.getName());
+    setType(x, type);
+    return null;
+  }
+
+  @Override
+  public Void visitRedirectConstructorInvocation(DartRedirectConstructorInvocation x) {
+    Element element = x.getSymbol();
+    if (element != null) {
+      if (!element.getModifiers().isConstant()) {
+        expectedConstant(x);
+      }
+    }
+    x.visitChildren(this);
+    return null;
+  }
+
+  @Override
+  public Void visitStringInterpolation(DartStringInterpolation x) {
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitSuperExpression(DartSuperExpression x) {
+    // No need to traverse further - super() expressions are never constant
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitUnaryExpression(DartUnaryExpression x) {
+    x.visitChildren(this);
+
+    Type type = getMostSpecificType(x.getArg());
+    switch (x.getOperator()) {
+      case NOT:
+        if (checkBoolean(x, type)) {
+          x.setType(boolType);
+        }
+        break;
+      case SUB:
+        if (checkNumber(x, type)) {
+          x.setType(numType);
+        }
+        break;
+      case BIT_NOT:
+        if (checkInt(x, type)) {
+          x.setType(intType);
+        }
+        break;
+      default:
+        expectedConstant(x);
+    }
+    return null;
+  }
+
+  @Override
+  public Void visitArrayLiteral(DartArrayLiteral x) {
+    if (!x.isConst()) {
+      expectedConstant(x);
+    } else {
+      x.visitChildren(this);
+    }
+    return null;
+  }
+
+  @Override
+  public Void visitFunction(DartFunction x) {
+    // No need to traverse, functions are always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitFunctionObjectInvocation(DartFunctionObjectInvocation x) {
+    // No need to traverse, function object invocations are always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitIdentifier(DartIdentifier x) {
+    x.visitChildren(this);
+
+    Element element = x.getSymbol();
+    switch(ElementKind.of(element)) {
+      case FIELD:
+      case CONSTRUCTOR:
+      case VARIABLE:
+      case PARAMETER:

[ngeoffray, 2011/10/17 10:59:38]

It looks like this will say a library prefix or a class are constant. Since they
have to be a DartPropertyAccess, I think that if you remove the visitChildren in
DartPropertyAccess, you can safely do expectConstant for things other than
FIELD, CONSTRUCTOR, VARIABLE or PARAMETER. Or an AssertionError?

[zundel, 2011/10/17 14:14:26]

Added kind CLASS and an ICE for the cases not explicitly spelled out.  This is
the place where I need to hook in some recursive check for a compile time
constant, so I added a NONE case and left it commented out.

+      if (!element.getModifiers().isConstant()) {
+        expectedConstant(x);
+      } else {
+        setType(x, getMostSpecificType(x));
+      }
+      break;
+    }
+    return null;
+  }
+
+
+  @Override
+  public Void visitInvocation(DartInvocation x) {
+    // No need to traverse, invocations are always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitMapLiteral(DartMapLiteral x) {
+    if (!x.isConst()) {
+      expectedConstant(x);
+    } else {
+      x.visitChildren(this);
+    }
+    return null;
+  }
+
+  @Override
+  public Void visitMethodInvocation(DartMethodInvocation x) {
+    // No need to traverse, method invocations are always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitNewExpression(DartNewExpression x) {
+    if (!x.isConst()) {
+      expectedConstant(x);
+    } else {
+      x.visitChildren(this);
+    }
+    return null;
+  }
+
+
+  @Override
+  public Void visitThisExpression(DartThisExpression x) {
+    // No need to traverse, this expressions are always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  @Override
+  public Void visitUnqualifiedInvocation(DartUnqualifiedInvocation x) {
+    // No need to traverse, always disallowed.
+    expectedConstant(x);
+    return null;
+  }
+
+  /**
+   * Logs a general message "expected a constant expression" error.  Use a more
+   * specific error message when possible.
+   */
+  private void expectedConstant(DartNode x) {
+    context.resolutionError(x, DartCompilerErrorCode.EXPECTED_CONSTANT_EXPRESSION);
+  }
+
+  /**
+   * Determine the most specific type assigned to an expression node. Prefer the
+   * setting in the expression's symbol if present. Otherwise, use a type tagged
+   * in the expression node itself.
+   *
+   * @return a non <code>null</code> type value. Dynamic if none other can be
+   * determined.
+   */
+  private Type getMostSpecificType(DartExpression expr) {
+    // TODO(zundel): this routine needs to recursively resolve as compile time constants any
+    // symbols that have not yet been resolved.
+    Element element = (Element)expr.getSymbol();
+    switch (ElementKind.of(element)) {
+      case FIELD:
+        return ((FieldElement)element).getType();
+      case METHOD:
+        return ((MethodElement)element).getType();
+      case VARIABLE:
+        return((VariableElement)element).getType();
+      case CONSTRUCTOR:
+        return ((ConstructorElement)element).getType();
+      case NONE:
+        if (expr.getType() != null) {
+          return expr.getType();
+        }
+        return dynamicType;
+      default:
+        throw new InternalCompilerException("Unhandled element " + expr.toString()
+                                            + " kind: " + ElementKind.of(element));
+    }
+  }
+
+  private void setType(DartExpression x, Type type) {
+    Element element = (Element)x.getSymbol();
+    if (element != null) {
+      Elements.setType(element, type);
+    }
+    // Also set on the expression node itself.  Not every expression has a symbol.
+    x.setType(type);
+  }
+}