No state hint when the call that reaches the needed state has a conditional postcondition (mode == 2 ? a(this) : b(this)) #455

Impact: if the only call that reaches the needed state has a conditional postcondition (mode == 2 ? compressionExplicit(this) : startCompression(this)), the error gets no hint at all. That is exactly the case where a hint helps most, because the developer has to find both the call and the argument value.

Minimal reproducer (an external spec and a client, in one directory)

// ImageWriteParamRefinements.java
@ExternalRefinementsFor("javax.imageio.ImageWriteParam")
@StateSet({"startCompression", "compressionExplicit", "compressionSet"})
public interface ImageWriteParamRefinements {
    @StateRefinement(to = "startCompression(this)")
    void ImageWriteParam(Locale locale);

    @StateRefinement(to = "mode == 2 ? compressionExplicit(this) : startCompression(this)")
    void setCompressionMode(int mode);

    @StateRefinement(from = "compressionExplicit(this)", to = "compressionSet(this)")
    void setCompressionType(String compressionType);
}

// Recoder.java
public class Recoder {
    static ImageWriteParam params() {
        ImageWriteParam wParam = new ImageWriteParam(Locale.ROOT);
        wParam.setCompressionType("JPEG");
        return wParam;
    }
}

Actual (main @ 19991d3): found startCompression(wParam⁹) but expected compressionExplicit(wParam⁹), with no hints.

When setCompressionMode is written as from = "startCompression(this)", to = "compressionExplicit(this)" instead, the same program does get hints:

Hints:
  - Call wParam.setCompressionMode(int) before this call to move wParam from startCompression to compressionExplicit
  - In state startCompression, wParam can call: setCompressionMode(int)

Expected: a hint that also gives the condition, e.g. "Call wParam.setCompressionMode(int) with mode == 2 before this call to move wParam from startCompression to compressionExplicit".

Related: #381, which uses this same example.

Real-world scenario. One of the exercises for the error-message study is dcm4che's Transcoder. It calls setCompressionType without setCompressionMode(ImageWriteParam.MODE_EXPLICIT), which throws IllegalStateException: Compression mode not MODE_EXPLICIT!, and the developers fixed it by adding that call (40bf9c66). The state machine view shows the way out (setCompressionMode, mode == 2), but the error itself has no hint.

In VS Code (dcm4che study exercise, verifier main @ 19991d3, extension main @ 80bed18). The Verification tab has no hint:

The State Machine tab does show the way out, setCompressionMode with mode == 2: