T.P.PDF: reliably detect when TOC has changed.

Sometimes the TOC changes but there are no warnings: this happens
when no labels are present.  In this case we must rerun LaTeX.
So we now take the sha1 hash of the TOC file and rerun LaTeX if it
changes between runs.

Closes #9295.

src/Text/Pandoc/PDF.hs

@@ -411,9 +411,10 @@ runTeXProgram program args tmpDir = do
                          , k /= "TEXINPUTS" && k /= "TEXMFOUTPUT"]
     liftIO (UTF8.readFile file) >>=
       showVerboseInfo (Just tmpDir) program programArgs env''
-    go file env'' programArgs (1 :: Int)
+    go file env'' programArgs (1 :: Int) Nothing
  where
-   go file env'' programArgs runNumber = do
+   go file env'' programArgs runNumber oldTocHash = do
+     let maxruns = 4 -- stop if warnings present after 4 runs
      report $ MakePDFInfo ("LaTeX run number " <> tshow runNumber) mempty
      (exit, out) <- liftIO $ E.catch
        (pipeProcess (Just env'') program programArgs BL.empty)
@@ -426,12 +427,23 @@ runTeXProgram program args tmpDir = do
                        then readFileLazy logFile
                        else return mempty
      let rerunWarnings = checkForRerun logContents
-     if not (null rerunWarnings) && runNumber < 4
+     tocHash <- do
+       let tocFile = replaceExtension file ".toc"
+       tocFileExists <- fileExists tocFile
+       if tocFileExists
+          then do
+            tocContents <- readFileLazy tocFile
+            pure $ Just $! sha1 tocContents
+          else pure Nothing
+     -- compare hash of toc to former hash to see if it changed (#9295)
+     let rerunWarnings' = rerunWarnings ++
+                           ["TOC changed" | tocHash /= oldTocHash ]
+     if not (null rerunWarnings') && runNumber < maxruns
         then do
           report $ MakePDFInfo "Rerun needed"
                     (T.intercalate "\n"
-                      (map (UTF8.toText . BC.toStrict) rerunWarnings))
-          go file env'' programArgs (runNumber + 1)
+                      (map (UTF8.toText . BC.toStrict) rerunWarnings'))
+          go file env'' programArgs (runNumber + 1) tocHash
        else do
           let pdfFile = replaceExtension file ".pdf"
           (log', pdf) <- getResultingPDF (Just logFile) pdfFile