compiletest silently fails on a name-value directive with a known name but missing colon but does not report an error

compiletest expects that a name-value directive, like //@ revisions: foo, to have the colon :

https://github.com/rust-lang/rust/blob/b14d8b2ef20c64c1002e2c6c724025c3d0846b91/src/tools/compiletest/src/header.rs#L1137-L1146

If the name-value directive contains a known directive name like revisions but does not have the colon (i.e. //@ revisions foo), then:

• compiletest known directive check accepts the known directive name revisions
• parse_name_value_directive expects revisions: but only got revisions, so parsing fails
• no other compiletest directive parsing rules accept revisions directive name
• no errors raised yet there is no effect (no revisions in this example).

compiletest should not silently fail here because it's very surprising and a pain to debug unless you know exactly what's wrong.

The relevant code is in src/tools/compiletest/src/header.rs around the linked lines, with parsing handled by parse_name_value_directive. Start there and trace how a known directive name without ':' is handled; done means the malformed directive reports an error instead of being silently ignored, with regression coverage in the relevant compiletest tests.