support for imgmath_latex=tectonic (#11281)

* add rudimentary support for using tectonic with imgmath

* fix typo

* addressing PR comment

* revert changes to preview.tex_t; add dvips by default for SVG

* bugfix

sphinx/ext/imgmath.py

@@ -80,13 +80,17 @@ def write_svg_depth(filename: str, depth: int) -> None:
 
 
 def generate_latex_macro(image_format: str,
-                         math: str, config: Config, confdir: str = '') -> str:
+                         math: str,
+                         config: Config,
+                         confdir: str = '') -> str:
     """Generate LaTeX macro."""
     variables = {
         'fontsize': config.imgmath_font_size,
         'baselineskip': int(round(config.imgmath_font_size * 1.2)),
         'preamble': config.imgmath_latex_preamble,
-        'tightpage': '' if image_format == 'png' else ',tightpage',
+        # the dvips option is important when imgmath_latex in ["xelatex", "tectonic"],
+        # it has no impact when imgmath_latex="latex"
+        'tightpage': '' if image_format == 'png' else ',dvips,tightpage',
         'math': math,
     }
 
@@ -123,10 +127,14 @@ def compile_math(latex: str, builder: Builder) -> str:
     with open(filename, 'w', encoding='utf-8') as f:
         f.write(latex)
 
+    imgmath_latex_name = path.basename(builder.config.imgmath_latex)
+
     # build latex command; old versions of latex don't have the
     # --output-directory option, so we have to manually chdir to the
     # temp dir to run it.
-    command = [builder.config.imgmath_latex, '--interaction=nonstopmode']
+    command = [builder.config.imgmath_latex]
+    if imgmath_latex_name not in ['tectonic']:
+        command.append('--interaction=nonstopmode')
     # add custom args from the config file
     command.extend(builder.config.imgmath_latex_args)
     command.append('math.tex')
@@ -134,7 +142,10 @@ def compile_math(latex: str, builder: Builder) -> str:
     try:
         subprocess.run(command, capture_output=True, cwd=tempdir, check=True,
                        encoding='ascii')
-        return path.join(tempdir, 'math.dvi')
+        if imgmath_latex_name in ['xelatex', 'tectonic']:
+            return path.join(tempdir, 'math.xdv')
+        else:
+            return path.join(tempdir, 'math.dvi')
     except OSError as exc:
         logger.warning(__('LaTeX command %r cannot be run (needed for math '
                           'display), check the imgmath_latex setting'),