8337680: failure_handler does not handle repeated commands well

[shivshah-oracle]

The failure handler keys each HTML section id by the command's name path, so when a command name occurs again after an intervening command - the same command repeated, or the same top-level tool reused, as in "jcmd.compiler.codecache jinfo jcmd.compiler.codelist" - a second section with the same id is written. Anchors and the data-toggle / data-show javascript resolve ids via document.getElementById, which returns the first match, so the later occurrence's output is unreachable. These are the two cases reported in the bug.

Fix: the root section keeps a registry of issued ids; a repeated id gets the first free numeric suffix ("jcmd-2", ...). Displayed names are unchanged, adjacent commands with a shared prefix still share their sections, children of a suffixed section are unique automatically, and the registry also prevents collisions with a command literally named like a suffix. The only external id reconstruction, ToolKit.link(), is keyed by PID and unaffected.

Ids can still repeat across appended fragments (each invocation appends a complete HTML document); that is pre-existing and tracked as JDK-8389541.

Verified with a standalone driver using both sequences from the bug: six duplicated ids before the fix, none after, every run's output reachable. New HtmlSectionTest (plain JUnit, like the existing unit tests) covers both reported cases, per-occurrence output association, triple repetition, the "jcmd-2" name collision, and the unchanged adjacent / shared-prefix behavior - 6/6 pass.

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• JDK-8337680: failure_handler does not handle repeated commands well (Bug - P4)

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