SpringBoot Banner placeholders use default values too soon

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.

Comment From: krzyk

@philwebb Can I work on this one?

Comment From: wilkinsona

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

Comment From: 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)"

Comment From: wilkinsona

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