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Improve prompt generating performance by caching prompt parts(%m, %M)#1127

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tompng merged 3 commits intoruby:masterfrom
tompng:prompt_main_string_performance
Oct 24, 2025
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Improve prompt generating performance by caching prompt parts(%m, %M)#1127
tompng merged 3 commits intoruby:masterfrom
tompng:prompt_main_string_performance

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@tompng tompng commented Oct 17, 2025

Fixes #1126

In prompt calculation, main.to_s was called on every keystroke and every line in multiline input.
Cache prompt parts(%m and %M) so that main.to_s is only called once per read-eval cycle.

Also fixes this problem.

irb(main):001> def self.to_s = 'a' * rand(1..10)
=> :to_s
# before
irb(aaa):002* def f 
irb(aaaaaaa):003*   puts 'Hello'
irb(aa):004*   puts 'World'
irb(aaaa):005> end

# after
irb(aaaa):002* def f
irb(aaaa):003*   puts 'Hello'
irb(aaaa):004*   puts 'World'
irb(aaaa):005> end

@tompng tompng force-pushed the prompt_main_string_performance branch from cd56ed4 to fdea403 Compare October 18, 2025 11:01
@tompng
Improve prompt generating performance by caching prompt parts(%m, %M)
35eb9e2 
In prompt calculation, `main.to_s` was called on every keystroke and every line in multiline input.
Cache prompt parts(%m, %M) so that `main.to_s` is only called once per read-eval cycle.
@tompng tompng force-pushed the prompt_main_string_performance branch from fdea403 to 35eb9e2 Compare October 18, 2025 11:05
st0012
st0012 reviewed Oct 18, 2025
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lib/irb.rb Outdated
end

def readmultiline
@prompt_part_cache = {}
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@st0012 st0012 Oct 18, 2025

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I think we can create a wrapper to ensure wherever we can generate prompt we have this set and cleaned. Like

with_prompt_part_cached do
  ...
end

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@tompng tompng Oct 18, 2025

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Nice catch! updated

st0012
st0012 approved these changes Oct 22, 2025
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@tompng @st0012
Add prompt_part_cache nil-able reason comment
4349ca3 
Co-authored-by: Stan Lo <stan001212@gmail.com>
@tompng tompng merged commit c95ee78 into ruby:master Oct 24, 2025
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@tompng tompng deleted the prompt_main_string_performance branch October 24, 2025 15:53
@tompng tompng added the enhancement New feature or request label Nov 1, 2025
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Bug: %m in default IRB prompt can make the console unusably slow for objects with huge to_s/inspect

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