[clang-tidy] Add check to detect dangling references in value handlers.

Summary:
Add check misc-dangling-handle to detect dangling references in value
handlers like std::experimental::string_view.
It provides a configuration option to specify other handle types that
should also be checked.

Right now it detects:
 - Construction from temporaries.
 - Assignment from temporaries.
 - Return statements from temporaries or locals.
 - Insertion into containers from temporaries.

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D17811

llvm-svn: 264759

2 files changed, 35 insertions, 0 deletions

diff --git a/clang-tools-extra/docs/clang-tidy/checks/list.rst b/clang-tools-extra/docs/clang-tidy/checks/list.rst
index 8e1bc15f0f4..36ea07fe359 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -50,6 +50,7 @@ Clang-Tidy Checks
    misc-assert-side-effect
    misc-assign-operator-signature
    misc-bool-pointer-implicit-conversion
+   misc-dangling-handle
    misc-definitions-in-headers
    misc-forward-declaration-namespace
    misc-inaccurate-erase
diff --git a/clang-tools-extra/docs/clang-tidy/checks/misc-dangling-handle.rst b/clang-tools-extra/docs/clang-tidy/checks/misc-dangling-handle.rst
new file mode 100644
index 00000000000..06601c68520
--- /dev/null
+++ b/clang-tools-extra/docs/clang-tidy/checks/misc-dangling-handle.rst
@@ -0,0 +1,34 @@
+.. title:: clang-tidy - misc-dangling-handle
+
+misc-dangling-handle
+====================
+
+Detect dangling references in value handlers like
+`std::experimental::string_view`.
+These dangling references can come from constructing handles from temporary
+values, where the temporary is destroyed soon after the handle is created.
+
+By default only `std::experimental::basic_string_view` is considered.
+This list can be modified by passing a ; separated list of class names using
+the HandleClasses option.
+
+Examples:
+
+.. code-block:: c++
+
+  string_view View = string();  // View will dangle.
+  string A;
+  View = A + "A";  // still dangle.
+
+  vector<string_view> V;
+  V.push_back(string());  // V[0] is dangling.
+  V.resize(3, string());  // V[1] and V[2] will also dangle.
+
+  string_view f() {
+    // All these return values will dangle.
+    return string();
+    string S;
+    return S;
+    char Array[10]{};
+    return Array;
+  }