Add `isInitCapture` and `forEachLambdaCapture` matchers.

[jcking1034]

Summary

This contributes follow-up work from https://reviews.llvm.org/D112491, which
allows for increased control over the matching of lambda captures. This also
updates the documentation for the lambdaCapture matcher.

[fowles]

clang/include/clang/ASTMatchers/ASTMatchers.h

4224

it would be nice to be able to do something like

int main() {
  int x, y;
  float z;
  auto f = [=, z]() { return x+ y + z; };
}

lambdaExpr(forEachLambdaCapture(isImplicit()) matches x and y but not z

[jcking1034]

Add additional unit tests.

[jcking1034]

clang/include/clang/ASTMatchers/ASTMatchers.h

4224

I believe that this should be possible, I've gone ahead and added some unit tests to demonstrate (see the tests named MatchImplicitCapturesOnly and MatchExplicitCapturesOnly).

[fowles]

That is awesome! Thanks for much for the examples. Everything here LGTM.

[ymandel]

clang/include/clang/ASTMatchers/ASTMatchers.h

4235

nice catch! i would have overlooked that detail.

[aaron.ballman]

LGTM!

clang/docs/LibASTMatchersReference.html

 "field" declarations in Clang parlance.
 
 Example matches a
   int a;
 </pre></td></tr>
 
 
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1LambdaCapture.html">LambdaCapture</a>&gt;</td><td class="name" onclick="toggle('lambdaCapture0')"><a name="lambdaCapture0Anchor">lambdaCapture</a></td><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1LambdaCapture.html">LambdaCapture</a>&gt;...</td></tr>
-<tr><td colspan="4" class="doc" id="lambdaCapture0"><pre></pre></td></tr>
+<tr><td colspan="4" class="doc" id="lambdaCapture0"><pre>Matches lambda captures.
+
+Given
+  int main() {
+    int x;
+    auto f = [x](){};
+    auto g = [x = 1](){};
+  }
+In the matcher `lambdaExpr(hasAnyCapture(lambdaCapture()))`,
+`lambdaCapture()` matches `x` and `x=1`.
+</pre></td></tr>
 
 
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NestedNameSpecifierLoc.html">NestedNameSpecifierLoc</a>&gt;</td><td class="name" onclick="toggle('nestedNameSpecifierLoc0')"><a name="nestedNameSpecifierLoc0Anchor">nestedNameSpecifierLoc</a></td><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NestedNameSpecifierLoc.html">NestedNameSpecifierLoc</a>&gt;...</td></tr>
 <tr><td colspan="4" class="doc" id="nestedNameSpecifierLoc0"><pre>Same as nestedNameSpecifier but matches NestedNameSpecifierLoc.
 </pre></td></tr>
 
 
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NestedNameSpecifier.html">NestedNameSpecifier</a>&gt;</td><td class="name" onclick="toggle('nestedNameSpecifier0')"><a name="nestedNameSpecifier0Anchor">nestedNameSpecifier</a></td><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1NestedNameSpecifier.html">NestedNameSpecifier</a>&gt;...</td></tr>

 
 
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1LambdaCapture.html">LambdaCapture</a>&gt;</td><td class="name" onclick="toggle('isImplicit2')"><a name="isImplicit2Anchor">isImplicit</a></td><td></td></tr>
 <tr><td colspan="4" class="doc" id="isImplicit2"><pre>Matches an entity that has been implicitly added by the compiler (e.g.
 implicit default/copy constructors).
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1LambdaExpr.html">LambdaExpr</a>&gt;</td><td class="name" onclick="toggle('forEachLambdaCapture0')"><a name="forEachLambdaCapture0Anchor">forEachLambdaCapture</a></td><td>LambdaCaptureMatcher InnerMatcher</td></tr>
+<tr><td colspan="4" class="doc" id="forEachLambdaCapture0"><pre>Matches each lambda capture in a lambda expression.
+
+Given
+  int main() {
+    int x, y;
+    float z;
+    auto f = [=]() { return x + y + z; };
+  }
+lambdaExpr(forEachLambdaCapture(
+    lambdaCapture(capturesVar(varDecl(hasType(isInteger()))))))
+will trigger two matches, binding for 'x' and 'y' respectively.
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1LambdaExpr.html">LambdaExpr</a>&gt;</td><td class="name" onclick="toggle('hasAnyCapture0')"><a name="hasAnyCapture0Anchor">hasAnyCapture</a></td><td>LambdaCaptureMatcher InnerMatcher</td></tr>
 <tr><td colspan="4" class="doc" id="hasAnyCapture0"><pre>Matches any capture in a lambda expression.
 
 Given
   void foo() {
     int t = 5;
     auto f = [=](){ return t; };
   }
Given:
   int z = 3;
 functionDecl(isExternC())
   matches the declaration of f and g, but not the declaration of h.
 varDecl(isExternC())
   matches the declaration of x and y, but not the declaration of z.
 </pre></td></tr>
 
 
+<tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1VarDecl.html">VarDecl</a>&gt;</td><td class="name" onclick="toggle('isInitCapture0')"><a name="isInitCapture0Anchor">isInitCapture</a></td><td></td></tr>
+<tr><td colspan="4" class="doc" id="isInitCapture0"><pre>Matches a variable serving as the implicit variable for a lambda init-
+capture.
+
+Example matches x (matcher = varDecl(isInitCapture()))
+auto f = [x=3]() { return x; };
+</pre></td></tr>
+
+
 <tr><td>Matcher&lt;<a href="https://clang.llvm.org/doxygen/classclang_1_1VarDecl.html">VarDecl</a>&gt;</td><td class="name" onclick="toggle('isStaticLocal0')"><a name="isStaticLocal0Anchor">isStaticLocal</a></td><td></td></tr>
 <tr><td colspan="4" class="doc" id="isStaticLocal0"><pre>Matches a static variable with local scope.
 
 Example matches y (matcher = varDecl(isStaticLocal()))
 void f() {
   int x;
   static int y;
 }

clang/include/clang/ASTMatchers/ASTMatchers.h

 AST_MATCHER_P(
     VarDecl, hasInitializer, internal::Matcher<Expr>,
     InnerMatcher) {
   const Expr *Initializer = Node.getAnyInitializer();
   return (Initializer != nullptr &&
           InnerMatcher.matches(*Initializer, Finder, Builder));
 }
 
+/// Matches a variable serving as the implicit variable for a lambda init-
+/// capture.
+///
+/// Example matches x (matcher = varDecl(isInitCapture()))
+/// \code
+/// auto f = [x=3]() { return x; };
+/// \endcode
+AST_MATCHER(VarDecl, isInitCapture) { return Node.isInitCapture(); }
+
+/// Matches each lambda capture in a lambda expression.
+///
+/// Given
+/// \code
+///   int main() {
+///     int x, y;
+///     float z;
+///     auto f = [=]() { return x + y + z; };
+///   }
+/// \endcode
+/// lambdaExpr(forEachLambdaCapture(
+///     lambdaCapture(capturesVar(varDecl(hasType(isInteger()))))))
+/// will trigger two matches, binding for 'x' and 'y' respectively.
+AST_MATCHER_P(LambdaExpr, forEachLambdaCapture, LambdaCaptureMatcher,
+              InnerMatcher) {
+  BoundNodesTreeBuilder Result;
+  bool Matched = false;
+  for (const auto &Capture : Node.captures()) {
+    if (Finder->isTraversalIgnoringImplicitNodes() && Capture.isImplicit())
+      continue;
+    BoundNodesTreeBuilder CaptureBuilder(*Builder);
+    if (InnerMatcher.matches(Capture, Finder, &CaptureBuilder)) {
+      Matched = true;
+      Result.addMatch(CaptureBuilder);
+    }
+  }
+  *Builder = std::move(Result);
+  return Matched;
+}
+
 /// \brief Matches a static variable with local scope.
 ///
 /// Example matches y (matcher = varDecl(isStaticLocal()))
 /// \code
 /// void f() {
 ///   int x;
 ///   static int y;
 /// }
for (const Expr *Arg : Node.arguments()) {
     if (InnerMatcher.matches(*Arg, Finder, &Result)) {
       *Builder = std::move(Result);
       return true;
     }
   }
   return false;
 }
 
+/// Matches lambda captures.
+///
+/// Given
+/// \code
+///   int main() {
+///     int x;
+///     auto f = [x](){};
+///     auto g = [x = 1](){};
+///   }
+/// \endcode
+/// In the matcher `lambdaExpr(hasAnyCapture(lambdaCapture()))`,
+/// `lambdaCapture()` matches `x` and `x=1`.
 extern const internal::VariadicAllOfMatcher<LambdaCapture> lambdaCapture;
 
 /// Matches any capture in a lambda expression.
 ///
 /// Given
 /// \code
 ///   void foo() {
 ///     int t = 5;

clang/lib/ASTMatchers/Dynamic/Registry.cpp

RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(floatLiteral);
   REGISTER_MATCHER(forCallable);
   REGISTER_MATCHER(forDecomposition);
   REGISTER_MATCHER(forEach);
   REGISTER_MATCHER(forEachArgumentWithParam);
   REGISTER_MATCHER(forEachArgumentWithParamType);
   REGISTER_MATCHER(forEachConstructorInitializer);
   REGISTER_MATCHER(forEachDescendant);
+  REGISTER_MATCHER(forEachLambdaCapture);
   REGISTER_MATCHER(forEachOverridden);
   REGISTER_MATCHER(forEachSwitchCase);
   REGISTER_MATCHER(forField);
   REGISTER_MATCHER(forFunction);
   REGISTER_MATCHER(forStmt);
   REGISTER_MATCHER(friendDecl);
   REGISTER_MATCHER(functionDecl);
   REGISTER_MATCHER(functionProtoType);
RegistryMaps::RegistryMaps() {
   REGISTER_MATCHER(isExplicitTemplateSpecialization);
   REGISTER_MATCHER(isExpr);
   REGISTER_MATCHER(isExternC);
   REGISTER_MATCHER(isFinal);
   REGISTER_MATCHER(isFirstPrivateKind);
   REGISTER_MATCHER(isImplicit);
   REGISTER_MATCHER(isInStdNamespace);
   REGISTER_MATCHER(isInTemplateInstantiation);
+  REGISTER_MATCHER(isInitCapture);
   REGISTER_MATCHER(isInline);
   REGISTER_MATCHER(isInstanceMessage);
   REGISTER_MATCHER(isInstanceMethod);
   REGISTER_MATCHER(isInstantiated);
   REGISTER_MATCHER(isInstantiationDependent);
   REGISTER_MATCHER(isInteger);
   REGISTER_MATCHER(isIntegral);
   REGISTER_MATCHER(isLambda);

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

 TEST_P(ASTMatchersTest, IsStaticLocal) {
   auto M = varDecl(isStaticLocal());
   EXPECT_TRUE(matches("void f() { static int X; }", M));
   EXPECT_TRUE(notMatches("static int X;", M));
   EXPECT_TRUE(notMatches("void f() { int X; }", M));
   EXPECT_TRUE(notMatches("int X;", M));
 }
 
+TEST_P(ASTMatchersTest, IsInitCapture) {
+  if (!GetParam().isCXX11OrLater()) {
+    return;
+  }
+  auto M = varDecl(hasName("vd"), isInitCapture());
+  EXPECT_TRUE(notMatches(
+      "int main() { int vd = 3; auto f = [vd]() { return vd; }; }", M));
+
+  if (!GetParam().isCXX14OrLater()) {
+    return;
+  }
+  EXPECT_TRUE(matches("int main() { auto f = [vd=3]() { return vd; }; }", M));
+  EXPECT_TRUE(matches(
+      "int main() { int x = 3; auto f = [vd=x]() { return vd; }; }", M));
+}
+
 TEST_P(ASTMatchersTest, StorageDuration) {
   StringRef T =
       "void f() { int x; static int y; } int a;static int b;extern int c;";
 
   EXPECT_TRUE(matches(T, varDecl(hasName("x"), hasAutomaticStorageDuration())));
   EXPECT_TRUE(
       notMatches(T, varDecl(hasName("y"), hasAutomaticStorageDuration())));
   EXPECT_TRUE(

clang/unittests/ASTMatchers/ASTMatchersTraversalTest.cpp

 }
 
 TEST(ForEachConstructorInitializer, MatchesInitializers) {
   EXPECT_TRUE(matches(
     "struct X { X() : i(42), j(42) {} int i, j; };",
     cxxConstructorDecl(forEachConstructorInitializer(cxxCtorInitializer()))));
 }
 
+TEST(ForEachLambdaCapture, MatchesCaptures) {
+  EXPECT_TRUE(matches(
+      "int main() { int x, y; auto f = [x, y]() { return x + y; }; }",
+      lambdaExpr(forEachLambdaCapture(lambdaCapture())), langCxx11OrLater()));
+  auto matcher = lambdaExpr(forEachLambdaCapture(
+      lambdaCapture(capturesVar(varDecl(hasType(isInteger())))).bind("LC")));
+  EXPECT_TRUE(matchAndVerifyResultTrue(
+      "int main() { int x, y; float z; auto f = [=]() { return x + y + z; }; }",
+      matcher, std::make_unique<VerifyIdIsBoundTo<LambdaCapture>>("LC", 2)));
+  EXPECT_TRUE(matchAndVerifyResultTrue(
+      "int main() { int x, y; float z; auto f = [x, y, z]() { return x + y + "
+      "z; }; }",
+      matcher, std::make_unique<VerifyIdIsBoundTo<LambdaCapture>>("LC", 2)));
+}
+
+TEST(ForEachLambdaCapture, IgnoreUnlessSpelledInSource) {
+  auto matcher =
+      traverse(TK_IgnoreUnlessSpelledInSource,
+               lambdaExpr(forEachLambdaCapture(
+                   lambdaCapture(capturesVar(varDecl(hasType(isInteger()))))
+                       .bind("LC"))));
+  EXPECT_TRUE(
+      notMatches("int main() { int x, y; auto f = [=]() { return x + y; }; }",
+                 matcher, langCxx11OrLater()));
+  EXPECT_TRUE(matchAndVerifyResultTrue(
+      "int main() { int x, y; float z; auto f = [=, &y]() { return x + y + z; "
+      "}; }",
+      matcher, std::make_unique<VerifyIdIsBoundTo<LambdaCapture>>("LC", 1)));
+}
+
 TEST(HasConditionVariableStatement, DoesNotMatchCondition) {
   EXPECT_TRUE(notMatches(
     "void x() { if(true) {} }",
     ifStmt(hasConditionVariableStatement(declStmt()))));
   EXPECT_TRUE(notMatches(
     "void x() { int x; if((x = 42)) {} }",
     ifStmt(hasConditionVariableStatement(declStmt()))));
 }