sagemathgh-36529: 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 with a coroutine and wait
for it (asynchronously) to return. Only when it has returned will we
delete the file it's viewing.

Closes: sagemath#36526
    
URL: sagemath#36529
Reported by: Michael Orlitzky
Reviewer(s): Eric Gourgoulhon

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