CPack: Add appimagetool environment options

The following options were added to complement what is possible
to control of appimagetool:
 - CPACK_APPIMAGE_ARCH
 - CPACK_APPIMAGE_SIGN_PASSPHRASE
 - CPACK_APPIMAGE_VERSION

Issue: #27556

Help/cpack_gen/appimage.rst

@@ -58,6 +58,14 @@ Qt plugins.
 You must also set :variable:`CPACK_PACKAGE_ICON` with the same value
 listed in the Desktop file.
 
+.. note::
+
+  The ``appimagetool`` uses environment variables to define its behavior.
+  These variables are exposed here for convenience, but it is also possible
+  to pass environment variables to it by setting the environment of a
+  :ref:`Package Preset` in a ``CMakePresets.json`` file, see
+  :manual:`cmake-presets(7)`.
+
 Variables Specific to CPack AppImage Generator
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -166,3 +174,34 @@ Variables Specific to CPack AppImage Generator
   :variable:`CPACK_APPIMAGE_SIGN`.
 
   :Default: Unset
+
+.. variable:: CPACK_APPIMAGE_SIGN_PASSPHRASE
+
+  .. versionadded:: 4.6
+
+  If the :variable:`CPACK_APPIMAGE_SIGN_KEY` is encrypted and requires a
+  passphrase to be used for signing (and, for some reason, GnuPG cannot be
+  used interactively, e.g., in a CI environment), this environment variable
+  can be used to safely pass the key.
+
+  :Default: Unset
+
+.. variable:: CPACK_APPIMAGE_ARCH
+
+  .. versionadded:: 4.6
+
+  Needs to be set whenever :variable:`CMAKE_SYSTEM_PROCESSOR` is not transformed
+  to a proper architecture and ``appimagetool`` cannot automatically determine the
+  architecture of the binaries inside the AppDir to choose a suitable runtime
+  (e.g., when binaries for multiple architectures or just shell scripts are
+  contained in there).
+
+  :Default: CMAKE_SYSTEM_PROCESSOR
+
+.. variable:: CPACK_APPIMAGE_VERSION
+
+  .. versionadded:: 4.6
+
+  This value will be inserted by appimagetool into the root desktop file.
+
+  :Default: :variable:`CPACK_PACKAGE_VERSION`

Help/release/dev/cpack-appimage.rst

@@ -0,0 +1,7 @@
+cpack-appimage
+--------------
+
+* The :cpack_gen:`CPack AppImage Generator` gained
+  :variable:`CPACK_APPIMAGE_VERSION`,
+  :variable:`CPACK_APPIMAGE_ARCH`, and
+  :variable:`CPACK_APPIMAGE_SIGN_PASSPHRASE` options.

Source/CPack/cmCPackAppImageGenerator.cxx

@@ -58,6 +58,30 @@ int cmCPackAppImageGenerator::InitializeInternal()
     return 0;
   }
 
+  if (cmValue packageVersion = this->GetOption("CPACK_PACKAGE_VERSION")) {
+    this->SetOptionIfNotSet("CPACK_APPIMAGE_VERSION", packageVersion);
+  }
+
+  if (!this->IsSet("CPACK_APPIMAGE_ARCH")) {
+    if (cmValue systemProcessor = this->GetOption("CMAKE_SYSTEM_PROCESSOR")) {
+      if (systemProcessor == "x86_64" || systemProcessor == "amd64") {
+        this->SetOption("CPACK_APPIMAGE_ARCH", "x86_64");
+      } else if (systemProcessor == "i386" || systemProcessor == "i686" ||
+                 systemProcessor == "x86") {
+        this->SetOption("CPACK_APPIMAGE_ARCH", "i686");
+      } else if (systemProcessor == "aarch64" || systemProcessor == "arm64") {
+        this->SetOption("CPACK_APPIMAGE_ARCH", "aarch64");
+      } else if (cmSystemTools::StringStartsWith(systemProcessor, "arm")) {
+        this->SetOption("CPACK_APPIMAGE_ARCH", "armhf");
+      } else {
+        cmCPackLogger(cmCPackLog::LOG_OUTPUT,
+                      "Could not transform CMAKE_SYSTEM_PROCESSOR, counting "
+                      "on appimagetool architecture detection."
+                        << std::endl);
+      }
+    }
+  }
+
   return Superclass::InitializeInternal();
 }
 
@@ -298,6 +322,13 @@ int cmCPackAppImageGenerator::PackageFiles()
     }
   };
 
+  auto addEnvOption = [this](std::string const& op, std::string envName) {
+    auto opt = this->GetOption(op);
+    if (opt) {
+      cmSystemTools::PutEnv(cmStrCat(envName, '=', *opt));
+    }
+  };
+
   addOption("CPACK_APPIMAGE_UPDATE_INFORMATION", "--updateinformation");
 
   addOptionFlag("CPACK_APPIMAGE_GUESS_UPDATE_INFORMATION", "--guess");
@@ -316,6 +347,13 @@ int cmCPackAppImageGenerator::PackageFiles()
 
   addOption("CPACK_APPIMAGE_SIGN_KEY", "--sign-key");
 
+  addEnvOption("CPACK_APPIMAGE_ARCH", "ARCH");
+
+  addEnvOption("CPACK_APPIMAGE_SIGN_PASSPHRASE",
+               "APPIMAGETOOL_SIGN_PASSPHRASE");
+
+  addEnvOption("CPACK_APPIMAGE_VERSION", "VERSION");
+
   cmCPackLogger(cmCPackLog::LOG_OUTPUT,
                 "Running AppImageTool: "
                   << cmSystemTools::PrintSingleCommand(command) << std::endl);