Package inputenc Error: Unicode char ̀ (U+300) (inputenc) not set up for use with LaTeX

Question

I am struggling understanding how to solve this error:

Package inputenc Error: Unicode char ̀ (U+300) (inputenc) not set up for use with LaTeX.

I have seen this related question, but the problem is that I have no idea where I have used this character and it seems I can't find it with find command.

Answer 1

U+0300 is a combining grave accent. PDFTeX and the 8-bit inputenc package cannot handle combining Unicode characters, only precomposed characters (NFC form).

The following MWE will reproduce your bug, if compiled in PDFTeX:

\documentclass{article}
\tracinglostchars=2
\usepackage[T1]{fontenc}

\begin{document}
à
\end{document}

This is because à is in decomposed form (U+0061 U+0300) instead of the NFC form, à (U+00E0). This is just one example, and there are several other places it could appear. (The most-famous example in English probably is Shakespare’s use of “punishèd.”)

If you compile with LuaLaTeX instead of PDFLaTeX, the engine will understand the combining character, but your 8-bit font will not contain it, so it will not display. The \tracinglostchars=2 line will at least give you a warning message about it.

Since the code I gave would never have compiled, though, it’s not likely that your old document has anything like that in it. Some users report that \'{\i} in their bibliographies causes this bug. In old versions of TeX, you needed to superimpose accents on a dotless ı, not over an i with a dot. That is no longer necessary, as \'{i} will be defined as a text composite.

This gives you the following options:

Use a Unicode Engine

If you remove the 8-bit font packages such as fontenc and inputenc, and compile with LuaTeX or XeTeX, it works:

\documentclass{article}
\tracinglostchars=2
\usepackage{fontspec}

\begin{document}
à
\end{document}

Convert to Precomposed Characters

I happen to have written a little program that normalizes UTF-8 input to NFC form, or you can do a search-and-replace.

This works, because it contains no combining characters, only precomposed characters:

\documentclass{article}
\tracinglostchars=2
\usepackage[T1]{fontenc}

\begin{document}
à
\end{document}

Use Accent Macros

If you must use PDFTeX, and there is no precomposed character for the the grapheme you want, you could write it as

\documentclass{article}
\tracinglostchars=2
\usepackage[T1]{fontenc}

\begin{document}
\`{a}
\end{document}