src/sage/misc/latex.py: fix view()

Rewriting the view() function to use python's tempfile module instead
of sage's own tmp_dir() accidentally broke this function, because the
viewer program needs the file to be slightly less temporary than we
made it. The viewer would launch, but then view() would immediately
return, causing the file that the viewer was about to look for to be
deleted.

To fix it, we now launch the viewer program synchronously within a
helper function, but launch that helper function asynchronously in a
new thread. This allows us to clean up the temporary directory only
after the subprocess has completed, but still lets view() return
immediately.

Closes: #36526

src/sage/misc/latex.py

@@ -29,7 +29,7 @@
 import random
 import re
 import shutil
-from subprocess import call, PIPE
+from subprocess import call, run, PIPE
 from tempfile import TemporaryDirectory
 
 from sage.misc.cachefunc import cached_function, cached_method
@@ -1923,27 +1923,48 @@ def view(objects, title='Sage', debug=False, sep='', tiny=False,
     if pdflatex or (viewer == "pdf" and engine == "latex"):
         engine = "pdflatex"
     # command line or notebook with viewer
-    with TemporaryDirectory() as tmp:
-        tex_file = os.path.join(tmp, "sage.tex")
-        with open(tex_file, 'w') as file:
-            file.write(s)
-        suffix = _run_latex_(tex_file, debug=debug, engine=engine, png=False)
-        if suffix == "pdf":
-            from sage.misc.viewer import pdf_viewer
-            viewer = pdf_viewer()
-        elif suffix == "dvi":
-            from sage.misc.viewer import dvi_viewer
-            viewer = dvi_viewer()
-        else:
-            print("Latex error")
-            return
-        output_file = os.path.join(tmp, "sage." + suffix)
-        # this should get changed if we switch the stuff in misc.viewer to
-        # producing lists
-        if debug:
-            print('viewer: "{}"'.format(viewer))
-        call('%s %s' % (viewer, output_file), shell=True,
-             stdout=PIPE, stderr=PIPE)
+
+    # We can't automatically delete the temporary file in this case
+    # because we need it to live at least long enough for the viewer
+    # to open it. Since we're launching the viewer asynchronously,
+    # that would be tricky.
+    tmp = TemporaryDirectory()
+
+    tex_file = os.path.join(tmp.name, "sage.tex")
+    with open(tex_file, 'w') as file:
+        file.write(s)
+    suffix = _run_latex_(tex_file, debug=debug, engine=engine, png=False)
+    if suffix == "pdf":
+        from sage.misc.viewer import pdf_viewer
+        viewer = pdf_viewer()
+    elif suffix == "dvi":
+        from sage.misc.viewer import dvi_viewer
+        viewer = dvi_viewer()
+    else:
+        print("Latex error")
+        tmp.cleanup()
+        return
+    output_file = os.path.join(tmp.name, "sage." + suffix)
+    # this should get changed if we switch the stuff in misc.viewer to
+    # producing lists
+    if debug:
+        print('viewer: "{}"'.format(viewer))
+
+    # Return immediately but only clean up the temporary file after
+    # the viewer has closed. This function is synchronous and waits
+    # for the process to complete...
+    def run_viewer():
+        run([viewer, output_file], capture_output=True)
+        tmp.cleanup()
+
+    # ...but we execute it asynchronously so that view() completes
+    # immediately. The "daemon" flag is important because, without it,
+    # sage won't quit until the viewer does.
+    from threading import Thread
+    t = Thread(target=run_viewer)
+    t.daemon = True
+    t.start()
+
     return