expand template vars in targets config

internal/crosscompile/crosscompile_test.go

@@ -301,3 +301,126 @@ func TestUseWithTarget(t *testing.T) {
 		t.Error("Expected LDFLAGS to be set for native build")
 	}
 }
+
+func TestExpandEnv(t *testing.T) {
+	envs := map[string]string{
+		"port": "/dev/ttyUSB0",
+		"hex":  "firmware.hex",
+		"bin":  "firmware.bin",
+		"root": "/usr/local/llgo",
+	}
+
+	tests := []struct {
+		template string
+		expected string
+	}{
+		{
+			"avrdude -c arduino -p atmega328p -P {port} -U flash:w:{hex}:i",
+			"avrdude -c arduino -p atmega328p -P /dev/ttyUSB0 -U flash:w:firmware.hex:i",
+		},
+		{
+			"simavr -m atmega328p -f 16000000 {}",
+			"simavr -m atmega328p -f 16000000 firmware.hex", // {} expands to hex (first priority)
+		},
+		{
+			"-I{root}/lib/CMSIS/CMSIS/Include",
+			"-I/usr/local/llgo/lib/CMSIS/CMSIS/Include",
+		},
+		{
+			"no variables here",
+			"no variables here",
+		},
+		{
+			"",
+			"",
+		},
+	}
+
+	for _, test := range tests {
+		result := expandEnv(test.template, envs)
+		if result != test.expected {
+			t.Errorf("expandEnv(%q) = %q, want %q", test.template, result, test.expected)
+		}
+	}
+}
+
+func TestExpandEnvSlice(t *testing.T) {
+	envs := map[string]string{
+		"root": "/usr/local/llgo",
+		"port": "/dev/ttyUSB0",
+	}
+
+	input := []string{
+		"-I{root}/include",
+		"-DPORT={port}",
+		"static-flag",
+	}
+
+	expected := []string{
+		"-I/usr/local/llgo/include",
+		"-DPORT=/dev/ttyUSB0",
+		"static-flag",
+	}
+
+	result := expandEnvSlice(input, envs)
+
+	if len(result) != len(expected) {
+		t.Fatalf("expandEnvSlice length mismatch: got %d, want %d", len(result), len(expected))
+	}
+
+	for i, exp := range expected {
+		if result[i] != exp {
+			t.Errorf("expandEnvSlice[%d] = %q, want %q", i, result[i], exp)
+		}
+	}
+}
+
+func TestExpandEnvWithDefault(t *testing.T) {
+	envs := map[string]string{
+		"port": "/dev/ttyUSB0",
+		"hex":  "firmware.hex",
+		"bin":  "firmware.bin",
+		"img":  "image.img",
+	}
+
+	tests := []struct {
+		template     string
+		defaultValue string
+		expected     string
+	}{
+		{
+			"simavr {}",
+			"", // No default - should use hex (priority)
+			"simavr firmware.hex",
+		},
+		{
+			"simavr {}",
+			"custom.elf", // Explicit default
+			"simavr custom.elf",
+		},
+		{
+			"qemu -kernel {}",
+			"vmlinux", // Custom kernel
+			"qemu -kernel vmlinux",
+		},
+		{
+			"no braces here",
+			"ignored",
+			"no braces here",
+		},
+	}
+
+	for i, test := range tests {
+		var result string
+		if test.defaultValue == "" {
+			result = expandEnvWithDefault(test.template, envs)
+		} else {
+			result = expandEnvWithDefault(test.template, envs, test.defaultValue)
+		}
+
+		if result != test.expected {
+			t.Errorf("Test %d: expandEnvWithDefault(%q, envs, %q) = %q, want %q",
+				i, test.template, test.defaultValue, result, test.expected)
+		}
+	}
+}