fix: use pre-installed Amazon.Lambda.Tools for dotnet6 builds

aws_lambda_builders/workflows/dotnet_clipackage/actions.py

@@ -28,9 +28,21 @@ class GlobalToolInstallAction(BaseAction):
     DESCRIPTION = "Install or update the Amazon.Lambda.Tools .NET Core Global Tool."
     PURPOSE = Purpose.COMPILE_SOURCE
 
-    def __init__(self, subprocess_dotnet):
+    def __init__(self, subprocess_dotnet, runtime=None):
         super(GlobalToolInstallAction, self).__init__()
         self.subprocess_dotnet = subprocess_dotnet
+        self.runtime = runtime
+
+    def _existing_tool_available(self):
+        """
+        Returns True if a working Amazon.Lambda.Tools is already available on the PATH
+        (e.g. pre-installed in the SAM build image).
+        """
+        try:
+            self.subprocess_dotnet.run(["lambda", "help"])
+            return True
+        except DotnetCLIExecutionError:
+            return False
 
     def execute(self):
         # run Amazon.Lambda.Tools update in sync block in case build is triggered in parallel
@@ -42,6 +54,15 @@ def execute(self):
                 LOG.info("Skipping to update Amazon.Lambda.Tools install/update, since it is updated recently")
                 return
 
+            # Amazon.Lambda.Tools 7.0.0 dropped support for dotnet6 (EOL runtime), so
+            # installing/updating to latest breaks dotnet6 builds. If a working tool is
+            # already available (e.g. pre-installed in the SAM build image), use it as is.
+            # Deliberately not setting __tools_installed here so other runtimes in the
+            # same process still install/update to latest as before.
+            if self.runtime == "dotnet6" and self._existing_tool_available():
+                LOG.info("Skipping Amazon.Lambda.Tools install/update for dotnet6; using the pre-installed version")
+                return
+
             try:
                 LOG.debug("Installing Amazon.Lambda.Tools Global Tool")
                 self.subprocess_dotnet.run(["tool", "install", "-g", "Amazon.Lambda.Tools", "--ignore-failed-sources"])

aws_lambda_builders/workflows/dotnet_clipackage/workflow.py

@@ -29,7 +29,7 @@ def __init__(self, source_dir, artifacts_dir, scratch_dir, manifest_path, runtim
 
         options = kwargs["options"] if "options" in kwargs else {}
         subprocess_dotnetcli = SubprocessDotnetCLI(os_utils=OSUtils())
-        dotnetcli_install = GlobalToolInstallAction(subprocess_dotnet=subprocess_dotnetcli)
+        dotnetcli_install = GlobalToolInstallAction(subprocess_dotnet=subprocess_dotnetcli, runtime=runtime)
 
         dotnetcli_deployment = RunPackageAction(
             source_dir,

tests/unit/workflows/dotnet_clipackage/test_actions.py

@@ -62,6 +62,43 @@ def test_global_tool_parallel(self):
             ["tool", "install", "-g", "Amazon.Lambda.Tools", "--ignore-failed-sources"]
         )
 
+    def test_dotnet6_skips_install_when_tool_preinstalled(self):
+        # `dotnet lambda help` succeeds -> a working tool is already available (e.g. SAM build image)
+        action = GlobalToolInstallAction(self.subprocess_dotnet, runtime="dotnet6")
+        action.execute()
+        self.subprocess_dotnet.run.assert_called_once_with(["lambda", "help"])
+
+    def test_dotnet6_installs_when_no_tool_preinstalled(self):
+        # `dotnet lambda help` fails -> no tool available, fall back to normal install
+        self.subprocess_dotnet.run.side_effect = [DotnetCLIExecutionError(message="No tool"), None]
+        action = GlobalToolInstallAction(self.subprocess_dotnet, runtime="dotnet6")
+        action.execute()
+        self.subprocess_dotnet.run.assert_any_call(["lambda", "help"])
+        self.subprocess_dotnet.run.assert_any_call(
+            ["tool", "install", "-g", "Amazon.Lambda.Tools", "--ignore-failed-sources"]
+        )
+
+    def test_other_runtimes_do_not_probe_for_preinstalled_tool(self):
+        action = GlobalToolInstallAction(self.subprocess_dotnet, runtime="dotnet8")
+        action.execute()
+        self.subprocess_dotnet.run.assert_called_once_with(
+            ["tool", "install", "-g", "Amazon.Lambda.Tools", "--ignore-failed-sources"]
+        )
+
+    def test_dotnet8_after_dotnet6_skip_still_installs(self):
+        # dotnet6 skips because a working tool is pre-installed, but it must NOT mark the
+        # tool as installed for the process - a subsequent dotnet8 build still installs
+        # or updates to latest as before
+        dotnet6_action = GlobalToolInstallAction(self.subprocess_dotnet, runtime="dotnet6")
+        dotnet6_action.execute()
+        self.subprocess_dotnet.reset_mock()
+
+        dotnet8_action = GlobalToolInstallAction(self.subprocess_dotnet, runtime="dotnet8")
+        dotnet8_action.execute()
+        self.subprocess_dotnet.run.assert_called_once_with(
+            ["tool", "install", "-g", "Amazon.Lambda.Tools", "--ignore-failed-sources"]
+        )
+
 
 class TestRunPackageAction(TestCase):
     @patch("aws_lambda_builders.workflows.dotnet_clipackage.dotnetcli.SubprocessDotnetCLI")