RFR: 8333211: NMT Reports: replace manual indentation handling with auto indent [v2]

[Ashutosh Mehra]

On Tue, 4 Jun 2024 11:47:29 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Hi,
>> 
>> this is the first of a few patches I plan to reduce NMT code complexity.
>> 
>> In NMT reporting, indentations are manually hard-coded. That makes the code brittle and frustrating to maintain. One cannot, e.g., re-use a printing subfunction in differently aligned portions without some awkward gymnastics (e.g. handing indentation as argument to the sub routine).
>> 
>> This patch adds a simple automatic indentation feature to `outputStream` and then uses that feature to simplify NMT reporting. NMT reporting becomes more malleable and easier to change. 
>> 
>> I plan to reuse this feature for a couple of non-NMT things.
>> 
>> ---
>> 
>> The new "autoindent" mode in `outputStream` is off by default. If enabled, the stream automatically adds indentations at new lines.
>> 
>> The added code is small and minimally invasive. It builds atop the existing manual indentation. It trades completeness for simplicity: 
>> - it only works for a selected set of APIs (`print`, `print_cr`, `print_raw`, `print_raw_cr`). 
>> - it does not work for multiline output: `print("line\nline\nline")` needs to be broken up into individual `print` calls
>> 
>> Despite these limitations, the feature works fine and I expect covers 99% of all use cases.
>> 
>> In the NMT reports, I replaced the many manual indentations with a few incarnations of `streamIndentor`. The changes in detail:
>> 
>> - to prevent backward compatibility issues, I am careful to limit the autoindent mode to NMT reporting.
>> - I replaced manual indentation with a few `streamIndentor` placements
>> - I removed the now useless `print_(malloc|virtual_memory|arena)_line`
>> 
>> - Some minor cleanups:
>>   - merged the `outputStream` constructors into one
>>   - moved indentation level and autoindent flag to the private section of `outputStream`
>>   - removed some unused accessors in `outputStream`
>>   - tightened printing code in NMT reporting, e.g. replaced `print_cr(" ")` with `cr()`
>>   - removed the now unused `NativeCallStack::print_on(outputStream* out, int indent)` which hands in indentation. 
>> 
>> The last point I see as the real benefit of autoindent; we now don't have to manually hand indentation levels to printing subroutines. Subroutines can be oblivious to indentation - their printouts will be correctly indented regardless of indentation level.
>> 
>> -----
>> 
>> Testing:
>> 
>> - GHAs
>> - I ran NMT jtreg tests manually
>> - I was careful to preserve the formatting of the existing reports. Therefore I tested all four variants: ...
>
> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - restore indentation() accessor
>  - Merge branch 'master' into nmt-reporting-better-indentation
>  - NMT reporting, better indentation

Looks good to me

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Marked as reviewed by asmehra (Committer).

PR Review: https://git.openjdk.org/jdk/pull/19461#pullrequestreview-2102888693