Improvements to Makefile (#370)

Improvement to `Makefile`. Also see
apple/container#822.

Author: dkovba

Makefile

@@ -13,10 +13,9 @@
 # limitations under the License.
 
 # Build configuration variables
-# The default version ID 0.0.0 indicates a local development build or PRB
 BUILD_CONFIGURATION ?= debug
 WARNINGS_AS_ERRORS ?= true
-SWIFT_CONFIGURATION = $(if $(filter-out false,$(WARNINGS_AS_ERRORS)),-Xswiftc -warnings-as-errors)
+SWIFT_CONFIGURATION := $(if $(filter-out false,$(WARNINGS_AS_ERRORS)),-Xswiftc -warnings-as-errors)
 
 # Commonly used locations
 SWIFT := "/usr/bin/swift"

vminitd/Makefile

@@ -14,17 +14,17 @@
 
 BUILD_CONFIGURATION := debug
 WARNINGS_AS_ERRORS ?= true
-SWIFT_WARNING_CONFIG = $(if $(filter-out false,$(WARNINGS_AS_ERRORS)),-Xswiftc -warnings-as-errors)
+SWIFT_WARNING_CONFIG := $(if $(filter-out false,$(WARNINGS_AS_ERRORS)),-Xswiftc -warnings-as-errors)
 SWIFT_CONFIGURATION := --swift-sdk aarch64-swift-linux-musl $(SWIFT_WARNING_CONFIG)
 
-SWIFT_VERSION = 6.2
-SWIFT_SDK_URL = https://download.swift.org/swift-6.2-release/static-sdk/swift-6.2-RELEASE/swift-6.2-RELEASE_static-linux-0.0.1.artifactbundle.tar.gz
-SWIFT_SDK_PATH = /tmp/$(notdir $(SWIFT_SDK_URL))
+SWIFT_VERSION := 6.2
+SWIFT_SDK_URL := https://download.swift.org/swift-6.2-release/static-sdk/swift-6.2-RELEASE/swift-6.2-RELEASE_static-linux-0.0.1.artifactbundle.tar.gz
+SWIFT_SDK_PATH := /tmp/$(notdir $(SWIFT_SDK_URL))
 
 SWIFTLY_URL := https://download.swift.org/swiftly/darwin/swiftly.pkg
-SWIFTLY_FILENAME = $(notdir $(SWIFTLY_URL))
+SWIFTLY_FILENAME := $(notdir $(SWIFTLY_URL))
 SWIFTLY_BIN_DIR ?= ~/.swiftly/bin
-VMINITD_BIN_PATH := $(shell swift build -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --show-bin-path)
+BUILD_BIN_DIR := $(shell swift build -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --show-bin-path)
 
 MACOS_VERSION := $(shell sw_vers -productVersion)
 MACOS_MAJOR := $(shell echo $(MACOS_VERSION) | cut -d. -f1)
@@ -40,8 +40,8 @@ all:
 	@rm -f ./bin/vmexec
 	@swift --version
 	@swift build -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION)
-	@install "$(VMINITD_BIN_PATH)/vminitd" ./bin/
-	@install "$(VMINITD_BIN_PATH)/vmexec" ./bin/
+	@install "$(BUILD_BIN_DIR)/vminitd" ./bin/
+	@install "$(BUILD_BIN_DIR)/vmexec" ./bin/
 
 .PHONY: cross-prep
 cross-prep: linux-sdk macos-sdk