War story: the hardest bug I ever debugged

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462 points jakevoytko | 1 comments | 24 Mar 25 14:37 UTC | HN request time: 0.001s | source

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epolanski ◴[27 Mar 25 14:16 UTC] No.43493909[source]▶

The worst bug I've ever encountered was a JS file that kept not running, with very cryptic and hard to understand trace that made no sense. TypeScript and others parsed it fine without any issues.

After 3 days of literally trying everything, I don't know why, I thought of rewriting the file character by character by hand and it worked. What was happening?

Eventually opened the two files side by side in a hex editor and here it is: several exotic unicode characters for "empty" space.

replies(2): >>43495967 #>>43496679 #

skeaker ◴[27 Mar 25 17:42 UTC] No.43495967[source]▶

>>43493909 #

I've seen this happen as the result of errant copy-pasting.

replies(1): >>43496380 #

1. shoo ◴[27 Mar 25 18:16 UTC] No.43496380[source]▶

>>43495967 #

I've seen this happen in enterprise systems integration work, where some data interchange spec is authored as a Word document, and it has tables defining valid string values for certain fields, and Word helpfully replaces plain ascii dashes in the string constants with pretty long dashes, and team A builds their side hand-typing these constants as plain ascii, and team B builds their side by copy-pasting the exact unicode strings out of the Word doc.

Not a hard thing to debug once the issue is noticed, and completely preventable (write specs in plain text).

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