Adding --target flag to build CMake target by name (#228)

src/fprime/fbuild/cli.py

@@ -12,7 +12,7 @@
 
 from fprime.common.utils import confirm
 from fprime.fbuild.builder import Build
-from fprime.fbuild.target import Target
+from fprime.fbuild.target import Target, DesignateTargetAction
 from fprime.fbuild.types import BuildType
 
 
@@ -180,12 +180,23 @@ def add_target_parser(
             if target.allows_pass_args()
             else ""
         )
-        parser.add_argument(
-            f"--{flag}",
-            action="store_true",
-            default=False,
-            help=f"{target.desc}{extra_help}",
-        )
+        # Target flag special handling
+        if flag == "target":
+            parser.add_argument(
+                f"--target",
+                type=str,
+                action=DesignateTargetAction,
+                default=None,
+                nargs=1,
+                help=f"{target.desc}",
+            )
+        else:
+            parser.add_argument(
+                f"--{flag}",
+                action="store_true",
+                default=False,
+                help=f"{target.desc}{extra_help}",
+            )
     for flag, description in filter(
         lambda flag_desc: flag_desc[0] not in flags, target.option_args()
     ):

src/fprime/fbuild/target.py

@@ -9,6 +9,7 @@
 import functools
 import itertools
 from abc import ABC, abstractmethod
+from argparse import Action
 from enum import Enum
 from pathlib import Path
 from typing import Dict, List, Set, Tuple
@@ -341,6 +342,43 @@ def is_supported(self, builder: "Build", context: Path):
         return self.build_target in build_target_names
 
 
+class DesignateTargetAction(Action):
+    """This class, when used as the action will set the target of all DesignatedBuildSystemTarget
+
+    argparse.Action actions can be used to handle custom behavior when parsing commands. This class will use the
+    --target flag to specify the build target on all known DesignatedBuildSystemTarget that have registered with this
+    class.
+    """
+
+    _DESIGNEES = []
+
+    @classmethod
+    def register_designee(cls, designee):
+        """Register designee to this action"""
+        cls._DESIGNEES.append(designee)
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        """Required __call__ function triggered by the parse"""
+        assert len(values) == 1, "Values object should contain 1 value"
+        for designee in self._DESIGNEES:
+            designee.set_target(values[0])
+        # The build target detection looks for true/false flags to be set. Mimic this by setting 'target' to True
+        setattr(namespace, "target", True)
+
+
+class DesignatedBuildSystemTarget(BuildSystemTarget):
+    """Invokes a designated target using the --target flag"""
+
+    def __init__(self, _, *args, **kwargs):
+        """Constructor setting child targets"""
+        super().__init__(None, *args, **kwargs)
+        DesignateTargetAction.register_designee(self)
+
+    def set_target(self, target):
+        """Set the target to build"""
+        self.build_target = target
+
+
 class DelegatorTarget(Target):
     """Delegates to another target
 

src/fprime/fbuild/target_definitions.py

@@ -6,7 +6,7 @@
 """
 
 from .gcovr import GcovrTarget
-from .target import BuildSystemTarget, TargetScope
+from .target import BuildSystemTarget, DesignatedBuildSystemTarget, TargetScope
 from .types import BuildType
 
 #### "build" targets for components, deployments, unittests for both normal and testing builds ####
@@ -27,12 +27,29 @@
 BuildSystemTarget(
     "all",
     mnemonic="build",
-    desc="Build components, ports, UTs, and deployments for unittest build",
+    desc="Build all components, ports, UTs, and deployments for unittest build",
     scope=TargetScope.GLOBAL,
     flags={"all", "ut"},
     build_type=BuildType.BUILD_TESTING,
 )
 
+DesignatedBuildSystemTarget(
+    "target",
+    mnemonic="build",
+    desc="Build a specific CMake target by name",
+    scope=TargetScope.GLOBAL,
+    flags={"target"},
+)
+
+DesignatedBuildSystemTarget(
+    "target",
+    mnemonic="build",
+    desc="Build a specific CMake target by name using the UT build",
+    scope=TargetScope.GLOBAL,
+    flags={"ut", "target"},
+    build_type=BuildType.BUILD_TESTING,
+)
+
 #### Check targets ####
 check = BuildSystemTarget(
     "check",