Diagnose LaTeX Compilation

Turn a failed build into a located, classified, minimally-fixed error. Never mass-rewrite the source to "make it compile", find the one thing that broke.

In Papyrus the app owns compilation (Cmd+S / Ctrl+S) and shows the AUTHOR a clickable diagnostics list. You cannot see that list: read the compiler log the app leaves in the project's top-level directory (<main>.log, named after the main .tex), or ask the author to paste the error. Do not run the compiler yourself in Papyrus (see papyrus-writing). Running the compiler directly applies only outside the app.

Step 1, Read the FIRST real error

Work from the first error, not the last: LaTeX errors cascade, and the tail of the log is usually damage from the head. The app's list is grouped by kind (file:line errors, then ! errors, then warnings, then boxes), not log order, and is parsed from only the last 20,000 characters of the final pass, so its top row may not be the first error; the .log on disk is complete. In a raw log, the first file:line: message (or ! …) line is the one to fix.

-file-line-error makes a compiler print file:line: message. If citations/refs are wrong (not the compile itself), the full cycle is pdflatex → bibtex/biber → pdflatex → pdflatex; Tectonic runs that cycle itself. In Papyrus, when the app compiles with pdflatex it runs the bibtex cycle for you if the document cites anything, but never biber: a biblatex document on the biber backend will not resolve its citations there, tell the author rather than editing around it.