Extensions not appended to graphics when file exists

[joel-coffman]

Brief outline of the bug

Not sure if this issue is a bug or simply inconsistent behavior due to kernel changes related to the handling of file names. When including an image and the file name contains a dot (.), known extensions (e.g., .png) are automatically appended unless a file with the "base" name exists when using LaTeX2e <2020-02-02> patch level 2. For example, including the image latex-project-logo.svg.png fails when the file latex-project-logo.svg exists. In contrast, prior versions compile successfully when both files exist.

Minimal example showing the bug

\RequirePackage{latexbug}       % <--should be always the first line (see CONTRIBUTING)!
\documentclass{article}

% Any preamble code goes here
\usepackage{graphicx}


\begin{document}

  % Demonstration of issue here
  \includegraphics{latex-project-logo.svg}
  
\end{document}

Compilation fails with the following error message:

LaTeX Error: Unknown graphics extension: .svg.

To be clear, the directory contains the following files:

• latex-project-logo.svg
• latex-project-logo.svg.png
• mwe.tex

Due to kernel changes related to the handling of file names, a slight change is needed to compile this document for older kernels:

-\includegraphics{latex-project-logo.svg}
+\includegraphics{{{latex-project-logo.svg}}}

With this change, the same document compiles on the following systems (pdfTeX and LaTeX versions copied from output):

• Ubuntu 18.04: pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian); LaTeX2e <2017-04-15>
• Ubuntu 19.10: pdfTeX, Version 3.14159265-2.6-1.40.20 (TeX Live 2019/Debian); LaTeX2e <2018-12-01>
• Debian 10: pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2019/dev/Debian); LaTeX2e <2018-12-01>

Log file (required) and possibly PDF file

mwe.log

latex-project-logo.svg.gz (compressed due to GitHub's restrictions on types of attachments)

[joel-coffman]

Commit dba9642 appears to contain some relevant code. Because latex-project-logo.svg exists, \Gin@ext is defined and so the code that appends extensions is skipped (see required/graphics/graphics.dtx line 1136 and following).

Possibly related issues / discussions:

• 2019-10-01 graphics release breaks formerly used {foo.bar}.png syntax for filenames with multiple dots (2019-10-01 graphics release breaks formerly used {foo.bar}.png syntax for filenames with multiple dots #204)
• Including files with "double extensions" or dots in their path (Including files with "double extensions" or dots in their path mrpiggi/svg#27)
• regression/bug in graphics inclusion with double extension (tex-live mailing list)