Banner placeholders use default values too soon

[Saucistophe]

The ResourceBanner uses placeholders with the regular syntax ${variable.name} syntax.

There are only a few variables supported, which is fine; and some of them, such as the application version, is not resolved when starting the project from IDE (as opposed from the jar).

I wanted to use default values, for instance ${application.version:dev}; when I do that, the printed version becomes dev regardless of whether it's defined.

I reproduced the issue in unit tests in ResourceBannerTests, and I think it is due to the way we handle resolvers:

for (PropertyResolver resolver : getPropertyResolvers(environment, sourceClass)) {
    banner = resolver.resolvePlaceholders(banner);
}

If the first resolver fails to find the value, it outputs the default value and it's final.

[krzyk]

@philwebb Can I work on this one?

[wilkinsona]

It's all yours, @krzyk. Thank you.

[Saucistophe]

If that can help, here is the test I wrote:

	@Test
	void renderDefaultValues() {
		Resource resource = new ByteArrayResource(
				"banner ${a}${spring-boot.formatted-version:default-value}".getBytes());
		String banner = printBanner(resource, "10.2", "2.0", null);
		assertThat(banner).startsWith("banner 1 (v10.2)");
	}

..Which yields:

java.lang.AssertionError: 
Expecting actual:
  "banner 1default-value
"
to start with:
  "banner 1 (v10.2)"

[wilkinsona]

Closing in favor of #34764. Thanks for the PR, @krzyk.