By default hpp files are not opened with CDT editor anymore if tm4e language pack is installed

[iloveeclipse]

Initially reported at tm4e: eclipse-tm4e/tm4e#437

1. Get 4.25 SDK
2. Create simple project and empty hello.hpp file
3. Install CDT SDK into it, restart
4. Double click on hello.hpp - it is opened in default C++ editor from CDT.
5. Right click in explorer -> "Open with" shows C++ editor in the proposed editors list
6. Close C++ editor.
7. Install org.eclipse.tm4e (TextMate support in Eclipse IDE, 0.5.1.202207061559) and org.eclipse.tm4e.language_pack (TextMate Language Pack, 0.1.0.202206131926)
8. Restart Eclipse
9. Double click on hello.hpp - it is opened in generic text editor, NOT with CDT C++ editor.
10. Right click in explorer -> "Open with" does NOT show C++ editor in the proposed editors list

Both CDT and tm4e define content types for hpp files, CDT with high prio, tm4e with low:
https://github.com/eclipse/tm4e/blob/972061af2add6231c5667e31f83d393c102bdf9b/org.eclipse.tm4e.language_pack/plugin.xml#L69

Commenting line above in tm4e plugin.xml fixes the issue.

This seem to be a bug in the platform. CDT contribution priority is high, tm4e is low. tm4e generic editor shouldn't ever be opened by default if CDT is installed.

However, interesting fact is that cpp files can still be opened with CDT C++ editor (even if tm4e also defines the content type for them, in the same line with hpp files).

May be related code:

eclipse.platform/runtime/bundles/org.eclipse.core.contenttype/src/org/eclipse/core/internal/content/ContentTypeCatalog.java

Line 47 in c198507

private final Comparator<IContentType> policyConstantGeneralIsBetter = (IContentType o1, IContentType o2) -> {

[mickaelistria]

The isuse is more on the policySpecificIsBetter which I believe editor association is using. It checks for the depth as an indicator of specialization, but this is only useful when comparing content type with one being an ancestor of the other (so we want the "child" to be used instead of the ancestor). In other cases, where content type are not on the same lineage, then the priority is more important than the depth.

[mickaelistria]

See also #350 and #351.

[jonahgraham]

Verified in I20230414-1800 that following steps in OP the C++ files open in CDT.