Bug 527553: Detect invalid decltype(auto) with a type specifier

The evaluated type of 'decltype(auto)' in combination with const and/or
volatile will be a ProblemType since this is not valid code. The patch
also contains a checker to give the user a visual feedback.

Note: A proposed quick-fix has been removed after a short discussion.

Change-Id: I8760ed0ac28e28529ab30516accac9c0413c87d9
Signed-off-by: Hansruedi Patzen <hansruedi.patzen@hsr.ch>

7 files changed, 296 insertions, 0 deletions

diff --git a/codan/org.eclipse.cdt.codan.checkers/OSGI-INF/l10n/bundle.properties b/codan/org.eclipse.cdt.codan.checkers/OSGI-INF/l10n/bundle.properties
index c5ebf9beed5..a478e7851e1 100644
--- a/codan/org.eclipse.cdt.codan.checkers/OSGI-INF/l10n/bundle.properties
+++ b/codan/org.eclipse.cdt.codan.checkers/OSGI-INF/l10n/bundle.properties
@@ -127,3 +127,7 @@ problem.description.UnusedStaticFunctionProblem = Finds static functions which c
 problem.messagePattern.UnusedStaticFunctionProblem = Unused static function ''{0}''
 problem.name.UnusedStaticFunctionProblem = Unused static function
 
+checker.name.DecltypeAutoChecker = Invalid 'decltype(auto)' specifier checker
+problem.name.DecltypeAutoProblem = Invalid 'decltype(auto)' specifier
+problem.messagePattern.DecltypeAutoProblem = Combining 'decltype(auto)' with other type specifiers is not allowed
+problem.description.DecltypeAutoProblem = This rule will flag 'decltype(auto)' if combined with other type specifiers
diff --git a/codan/org.eclipse.cdt.codan.checkers/plugin.xml b/codan/org.eclipse.cdt.codan.checkers/plugin.xml
index b4b1e025c35..7d44acf36d0 100644
--- a/codan/org.eclipse.cdt.codan.checkers/plugin.xml
+++ b/codan/org.eclipse.cdt.codan.checkers/plugin.xml
@@ -424,5 +424,20 @@
                name="Nesting comments">
          </problem>
       </checker>
+            <checker
+            class="org.eclipse.cdt.codan.internal.checkers.DecltypeAutoChecker"
+            id="org.eclipse.cdt.codan.internal.checkers.DecltypeAutoChecker"
+            name="%checker.name.DecltypeAutoChecker">
+         <problem
+               category="org.eclipse.cdt.codan.core.categories.ProgrammingProblems"
+               defaultEnabled="true"
+               defaultSeverity="Error"
+               description="%problem.description.DecltypeAutoProblem"
+               id="org.eclipse.cdt.codan.internal.checkers.DecltypeAutoProblem"
+               markerType="org.eclipse.cdt.codan.core.codanProblem"
+               messagePattern="%problem.messagePattern.DecltypeAutoProblem"
+               name="%problem.name.DecltypeAutoProblem">
+         </problem>
+      </checker>
    </extension>
 </plugin>
diff --git a/codan/org.eclipse.cdt.codan.checkers/src/org/eclipse/cdt/codan/internal/checkers/DecltypeAutoChecker.java b/codan/org.eclipse.cdt.codan.checkers/src/org/eclipse/cdt/codan/internal/checkers/DecltypeAutoChecker.java
new file mode 100644
index 00000000000..f071bbe217b
--- /dev/null
+++ b/codan/org.eclipse.cdt.codan.checkers/src/org/eclipse/cdt/codan/internal/checkers/DecltypeAutoChecker.java
@@ -0,0 +1,45 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Institute for Software, HSR Hochschule fuer Technik
+ * Rapperswil, University of applied sciences.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *******************************************************************************/
+package org.eclipse.cdt.codan.internal.checkers;
+
+import org.eclipse.cdt.codan.core.cxx.model.AbstractIndexAstChecker;
+import org.eclipse.cdt.core.dom.ast.ASTVisitor;
+import org.eclipse.cdt.core.dom.ast.IASTDeclSpecifier;
+import org.eclipse.cdt.core.dom.ast.IASTTranslationUnit;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPASTSimpleDeclSpecifier;
+
+public class DecltypeAutoChecker extends AbstractIndexAstChecker {
+	public static final String ERR_ID = "org.eclipse.cdt.codan.internal.checkers.DecltypeAutoProblem"; //$NON-NLS-1$
+
+	@Override
+	public boolean runInEditor() {
+		return true;
+	}
+
+	@Override
+	public void processAst(IASTTranslationUnit ast) {
+		ast.accept(new ASTVisitor() {
+			{
+				shouldVisitDeclSpecifiers = true;
+			}
+
+			@Override
+			public int visit(IASTDeclSpecifier specifier) {
+				if (specifier instanceof ICPPASTSimpleDeclSpecifier) {
+					if (((ICPPASTSimpleDeclSpecifier) specifier).getType() == ICPPASTSimpleDeclSpecifier.t_decltype_auto) {
+						if (specifier.isConst() || specifier.isVolatile()) {
+							reportProblem(ERR_ID, specifier);
+						}
+					}
+				}
+				return PROCESS_CONTINUE;
+			}
+		});
+	}
+}
diff --git a/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/internal/checkers/DecltypeAutoCheckerTest.java b/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/internal/checkers/DecltypeAutoCheckerTest.java
new file mode 100644
index 00000000000..3af9c505b04
--- /dev/null
+++ b/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/internal/checkers/DecltypeAutoCheckerTest.java
@@ -0,0 +1,171 @@
+/*******************************************************************************
+ * Copyright (c) 2017 Institute for Software, HSR Hochschule fuer Technik
+ * Rapperswil, University of applied sciences.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *******************************************************************************/
+package org.eclipse.cdt.codan.core.internal.checkers;
+
+import org.eclipse.cdt.codan.core.tests.CheckerTestCase;
+import org.eclipse.cdt.codan.internal.checkers.DecltypeAutoChecker;
+
+/**
+ * Test for {@link DecltypeAutoChecker} class
+ */
+public class DecltypeAutoCheckerTest extends CheckerTestCase {
+
+	public static final String ERR_ID = DecltypeAutoChecker.ERR_ID;
+
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+		enableProblems(ERR_ID);
+	}
+
+	@Override
+	public boolean isCpp() {
+		return true;
+	}
+
+	// int i { 42 }
+	// decltype(i) k = i;
+	public void testDecltypeExpressionVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// int i { 42 }
+	// decltype(i) volatile k = i;
+	public void testDecltypeExpressionVolatileVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// int i { 42 }
+	// decltype(i) const k = i;
+	public void testDecltypeExpressionConstVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// int i { 42 }
+	// decltype(i) const volatile k = i;
+	public void testDecltypeExpressionCVVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// decltype(auto) i { 42 };
+	public void testDecltypeAutoVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// decltype(auto) const i { 42 };
+	public void testDecltypeAutoConstVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// decltype(auto) volatile i { 42 };
+	public void testDecltypeAutoVolatileVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// decltype(auto) const volatile i { 42 };
+	public void testDecltypeAutoCVVariable() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// void foo() {
+	//   decltype(auto) const i { 42 };
+	// }
+	public void testDecltypeAutoConstVariablInsideFunction() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(2, ERR_ID);
+	}
+
+	// void foo() {
+	//   decltype(auto) volatile i { 42 };
+	// }
+	public void testDecltypeAutoVolatileVariableInsideFunction() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(2, ERR_ID);
+	}
+
+	// void foo() {
+	//   decltype(auto) const volatile i { 42 };
+	// }
+	public void testDecltypeAutoCVVariableInsideFunction() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(2, ERR_ID);
+	}
+
+	// decltype(auto) foo() {
+	//    return 42;
+	// }
+	public void testDecltypeAutoReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// decltype(auto) const foo() {
+	//    return 42;
+	// }
+	public void testDecltypeAutoConstReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// decltype(auto) volatile foo() {
+	//    return 42;
+	// }
+	public void testDecltypeAutoVolatileReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// decltype(auto) const volatile foo() {
+	//    return 42;
+	// }
+	public void testDecltypeAutoCVReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// auto foo() -> decltype(auto) {
+	//    return 42;
+	// }
+	public void testDecltypeAutoTrailingReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkNoErrorsOfKind(ERR_ID);
+	}
+
+	// auto foo() -> decltype(auto) const {
+	//    return 42;
+	// }
+	public void testDecltypeAutoConstTrailingReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// auto foo() -> decltype(auto) volatile {
+	//    return 42;
+	// }
+	public void testDecltypeAutoVolatileTrailingReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+
+	// auto foo() -> decltype(auto) const volatile {
+	//    return 42;
+	// }
+	public void testDecltypeAutoCVTrailingReturnType() throws Exception {
+		loadCodeAndRun(getAboveComment());
+		checkErrorLine(1, ERR_ID);
+	}
+}
diff --git a/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/tests/AutomatedIntegrationSuite.java b/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/tests/AutomatedIntegrationSuite.java
index 71bf0ca2620..57560947458 100644
--- a/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/tests/AutomatedIntegrationSuite.java
+++ b/codan/org.eclipse.cdt.codan.core.tests/src/org/eclipse/cdt/codan/core/tests/AutomatedIntegrationSuite.java
@@ -19,6 +19,7 @@ import org.eclipse.cdt.codan.core.internal.checkers.CatchByReferenceTest;
 import org.eclipse.cdt.codan.core.internal.checkers.ClassMembersInitializationCheckerTest;
 import org.eclipse.cdt.codan.core.internal.checkers.CommentCheckerLineTests;
 import org.eclipse.cdt.codan.core.internal.checkers.CommentCheckerNestedTests;
+import org.eclipse.cdt.codan.core.internal.checkers.DecltypeAutoCheckerTest;
 import org.eclipse.cdt.codan.core.internal.checkers.FormatStringCheckerTest;
 import org.eclipse.cdt.codan.core.internal.checkers.NonVirtualDestructorCheckerTest;
 import org.eclipse.cdt.codan.core.internal.checkers.ProblemBindingCheckerTest;
@@ -66,6 +67,7 @@ public class AutomatedIntegrationSuite extends TestSuite {
 		suite.addTestSuite(CaseBreakCheckerTest.class);
 		suite.addTestSuite(CatchByReferenceTest.class);
 		suite.addTestSuite(ClassMembersInitializationCheckerTest.class);
+		suite.addTestSuite(DecltypeAutoCheckerTest.class);
 		suite.addTestSuite(FormatStringCheckerTest.class);
 		suite.addTestSuite(NonVirtualDestructorCheckerTest.class);
 		suite.addTestSuite(ProblemBindingCheckerTest.class);
diff --git a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
index 1d1537171f7..dca395e394c 100644
--- a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
+++ b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
@@ -12268,6 +12268,9 @@ public class AST2CPPTests extends AST2CPPTestBase {
 	//	decltype(auto) j{42}; // Valid since C++17: decltype(j) is int
 	//	decltype(auto) k = new decltype(auto)(1L); // decltype(j) is long int *
 	//	decltype(auto) l; // Error - missing initializer.
+	//	decltype(auto) const m = 42; // Error - decltype(auto) does not allow type specifiers. Bug 527553
+	//	decltype(auto) volatile n = 42; // Error - decltype(auto) does not allow type specifiers. Bug 527553
+	//	decltype(auto) const volatile o = 42; // Error - decltype(auto) does not allow type specifiers. Bug 527553
 	public void testDecltypeAutoVariableTypes_482225() throws Exception {
 		String code = getAboveComment();
 		BindingAssertionHelper bh = new AST2AssertionHelper(code, true);
@@ -12306,6 +12309,54 @@ public class AST2CPPTests extends AST2CPPTestBase {
 		ICPPVariable l = bh.assertNonProblem("l;", 1);
 		IProblemType lType = (IProblemType) l.getType();
 		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE, lType.getID());
+
+		ICPPVariable m = bh.assertNonProblem("m =", 1);
+		IProblemType mType = (IProblemType) m.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE, mType.getID());
+
+		ICPPVariable n = bh.assertNonProblem("n =", 1);
+		IProblemType nType = (IProblemType) n.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE, nType.getID());
+
+		ICPPVariable o = bh.assertNonProblem("o =", 1);
+		IProblemType oType = (IProblemType) o.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE, oType.getID());
+	}
+
+	//	auto foo() -> decltype(auto) const {
+	//		return 23.0;
+	//	}
+	//	auto a = foo();
+	public void testDecltypeAutoTrailingReturnTypeConst_527553() throws Exception {
+		String code = getAboveComment();
+		BindingAssertionHelper bh = new AST2AssertionHelper(code, true);
+		ICPPVariable a = bh.assertNonProblem("a =", 1);
+		IProblemType aType = (IProblemType) a.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_AUTO_TYPE, aType.getID());
+	}
+
+	//	auto foo() -> decltype(auto) volatile {
+	//		return 23.0;
+	//	}
+	//  auto a = foo();
+	public void testDecltypeAutoTrailingReturnTypeVolatile_527553() throws Exception {
+		String code = getAboveComment();
+		BindingAssertionHelper bh = new AST2AssertionHelper(code, true);
+		ICPPVariable a = bh.assertNonProblem("a =", 1);
+		IProblemType aType = (IProblemType) a.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_AUTO_TYPE, aType.getID());
+	}
+
+	//	auto foo() -> decltype(auto) const {
+	//		return 23.0;
+	//	}
+	//	decltype(auto) a = foo();
+	public void testDecltypeAutoTrailingReturnTypeConstDecltype_527553() throws Exception {
+		String code = getAboveComment();
+		BindingAssertionHelper bh = new AST2AssertionHelper(code, true);
+		ICPPVariable a = bh.assertNonProblem("a =", 1);
+		IProblemType aType = (IProblemType) a.getType();
+		assertEquals(ISemanticProblem.TYPE_CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE, aType.getID());
 	}
 
 	//	auto foo() -> decltype(auto) {
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
index c24d6402b15..4ccbc5f2741 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
@@ -2270,6 +2270,10 @@ public class CPPVisitor extends ASTQueries {
 					// 'decltype(auto)' cannot be combined with * or & the way 'auto' can.
 					return ProblemType.CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE;
 				}
+				if (declSpec.isConst() || declSpec.isVolatile()) {
+					// 'decltype(auto)' cannot be combined with any type specifiers. [dcl.type.auto.deduct]
+					return ProblemType.CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE;
+				}
 				if (autoInitClause instanceof IASTExpression) {
 					return getDeclType((IASTExpression) autoInitClause);					
 				} else {
@@ -2392,6 +2396,10 @@ public class CPPVisitor extends ASTQueries {
 				// 'decltype(auto)' cannot be combined with * or & the way 'auto' can.
 				return ProblemType.CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE;
 			}
+			if (autoDeclSpec.isConst() || autoDeclSpec.isVolatile()) {
+				// 'decltype(auto)' cannot be combined with any type specifiers. [dcl.type.auto.deduct]
+				return ProblemType.CANNOT_DEDUCE_DECLTYPE_AUTO_TYPE;
+			}
 			return CPPSemantics.getDeclTypeForEvaluation(returnEval);
 		} else /* auto */ {
 			return createAutoType(returnEval, autoDeclSpec, autoDeclarator);