cpp: Add some convenience functions

* lang/cpp/src/context.cpp (Context::create): New.
* lang/cpp/src/context.h: Update accordingly.
* lang/cpp/src/key.cpp, lang/cpp/src/key.h:
(Key::isBad, Subkey::isBad, UserID::isBad)
(UserID::Signature::isBad): Add shorthand for the isX checks.
* NEWS: Mention it.

--
I don't know how often I wrote:
if (key.isNull() || key.isExpired() || key.isRevoked() ...

And for the context it is good practice to use a unique ptr
so the API should make it easy.

NEWS

@@ -1,6 +1,14 @@
 Noteworthy changes in version 1.12.1 (unreleased)
 -------------------------------------------------
 
+ * Interface changes relative to the 1.12.0 release:
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ cpp: Context::create                       NEW.
+ cpp: Key::isBad                            NEW.
+ cpp: Subkey::isBad                         NEW.
+ cpp: UserID::isBad                         NEW.
+ cpp: UserID::Signature::isBad              NEW.
+
 
 Noteworthy changes in version 1.12.0 (2018-10-08)
 -------------------------------------------------

lang/cpp/src/context.cpp

@@ -228,6 +228,11 @@ Context *Context::createForProtocol(Protocol proto)
     return new Context(ctx);
 }
 
+std::unique_ptr<Context> Context::create(Protocol proto)
+{
+  return std::unique_ptr <Context> (createForProtocol(proto));
+}
+
 std::unique_ptr<Context> Context::createForEngine(Engine eng, Error *error)
 {
     gpgme_ctx_t ctx = 0;

lang/cpp/src/context.h

@@ -68,6 +68,8 @@ public:
     //
 
     static Context *createForProtocol(Protocol proto);
+    /** Same as above but returning a unique ptr. */
+    static std::unique_ptr<Context> create(Protocol proto);
     static std::unique_ptr<Context> createForEngine(Engine engine, Error *err = 0);
     virtual ~Context();
 

lang/cpp/src/key.cpp

@@ -1033,6 +1033,26 @@ time_t Key::lastUpdate() const
     return static_cast<time_t>(key ? key->last_update : 0);
 }
 
+bool Key::isBad() const
+{
+    return isNull() || isRevoked() || isExpired() || isDisabled() || isInvalid();
+}
+
+bool Subkey::isBad() const
+{
+    return isNull() || isRevoked() || isExpired() || isDisabled() || isInvalid();
+}
+
+bool UserID::isBad() const
+{
+    return isNull() || isRevoked() || isInvalid();
+}
+
+bool UserID::Signature::isBad() const
+{
+    return isNull() || isExpired() || isInvalid();
+}
+
 std::ostream &operator<<(std::ostream &os, const UserID &uid)
 {
     os << "GpgME::UserID(";

lang/cpp/src/key.h

@@ -98,6 +98,10 @@ public:
     bool isDisabled() const;
     bool isInvalid() const;
 
+    /*! Shorthand for isNull || isRevoked || isExpired ||
+     *                          isDisabled || isInvalid */
+    bool isBad() const;
+
     bool canEncrypt() const;
     /*!
       This function contains a workaround for old gpgme's: all secret
@@ -250,6 +254,10 @@ public:
     bool isInvalid() const;
     bool isDisabled() const;
 
+    /*! Shorthand for isNull || isRevoked || isExpired ||
+     *                          isDisabled || isInvalid */
+    bool isBad() const;
+
     bool canEncrypt() const;
     bool canSign() const;
     bool canCertify() const;
@@ -366,6 +374,9 @@ public:
     bool isRevoked() const;
     bool isInvalid() const;
 
+    /*! Shorthand for isNull || isRevoked || isInvalid */
+    bool isBad() const;
+
     /** TOFU info for this userid.
      * @returns The TOFU stats or a null TofuInfo.
      */
@@ -454,6 +465,9 @@ public:
     bool isExpired() const;
     bool isExportable() const;
 
+    /*! Shorthand for isNull || isExpired || isInvalid */
+    bool isBad() const;
+
     const char *signerUserID() const;
     const char *signerName() const;
     const char *signerEmail() const;