From c96a660e4d38ec2d3c5fd25fa74a04bc47c62845 Mon Sep 17 00:00:00 2001
From: Lukas Schrangl <schrangl@iap.tuwien.ac.at>
Date: Sun, 4 Aug 2019 12:11:33 +0200
Subject: Run latex after bibtex/biber only when necessary

Although comments in src/engine/SCons/Tool/tex.py indicated that latex
should only be run after biber/bibtex if the .bbl file had changed, it
was always run.
---
 CHANGES.txt                    |  3 +++
 SCons/Tool/tex.py              |  4 ++--
 test/TEX/biber_biblatex2.py    | 17 ++++++++++++++---
 test/TEX/bibtex-latex-rerun.py | 16 +++++++++++++---
 4 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index cae5783..2308a2f 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1066,6 +1066,9 @@ RELEASE 3.1.1 - Mon, 07 Aug 2019 20:09:12 -0500
         - JSON encoding errors for CacheDir config
         - JSON decoding errors for CacheDir config
 
+  From Lukas Schrangl:
+    - Run LaTeX after biber/bibtex only if necessary
+
 
 RELEASE 3.1.0 - Mon, 20 Jul 2019 16:59:23 -0700
 
diff --git a/SCons/Tool/tex.py b/SCons/Tool/tex.py
index 6d0a5fb..b9dd29e 100644
--- a/SCons/Tool/tex.py
+++ b/SCons/Tool/tex.py
@@ -345,7 +345,7 @@ def InternalLaTeXAuxAction(XXXLaTeXAction, target = None, source= None, env=None
                         result = BibTeXAction(bibfile, bibfile, env)
                         if result != 0:
                             check_file_error_message(env['BIBTEX'], 'blg')
-                        must_rerun_latex = True
+                        check_MD5(suffix_nodes[".bbl"], ".bbl")
 
         # Now decide if biber will need to be run.
         # When the backend for biblatex is biber (by choice or default) the
@@ -369,7 +369,7 @@ def InternalLaTeXAuxAction(XXXLaTeXAction, target = None, source= None, env=None
                         result = BiberAction(bibfile, bibfile, env)
                         if result != 0:
                             check_file_error_message(env['BIBER'], 'blg')
-                        must_rerun_latex = True
+                        check_MD5(suffix_nodes[".bbl"], ".bbl")
 
         # Now decide if latex will need to be run again due to index.
         if check_MD5(suffix_nodes['.idx'],'.idx') or (count == 1 and run_makeindex):
diff --git a/test/TEX/biber_biblatex2.py b/test/TEX/biber_biblatex2.py
index 92c7ea9..049f06e 100644
--- a/test/TEX/biber_biblatex2.py
+++ b/test/TEX/biber_biblatex2.py
@@ -72,7 +72,7 @@ sources_bib_content = r"""
 """
 test.write(['ref.bib'],sources_bib_content % '2013' )
 
-test.write(['bibertest.tex'],r"""
+sources_tex_content = r"""
 \documentclass{article}
 
 \usepackage{biblatex}
@@ -80,13 +80,14 @@ test.write(['bibertest.tex'],r"""
 
 \begin{document}
 
-Hello. This is boring.
+Hello. This is %s boring.
 \cite{mybook}
 And even more boring.
 
 \printbibliography
 \end{document}
-""")
+"""
+test.write(['bibertest.tex'], sources_tex_content % "")
 
 
 test.run()
@@ -110,7 +111,17 @@ for f in files:
 pdf_output_1 = test.read('bibertest.pdf')
 
 
+# Change tex, but don't change bib. In this case, pdf should still be rebuilt.
+test.write(['bibertest.tex'], sources_tex_content % "very")
+test.run()
+pdf_output_1a = test.read('bibertest.pdf')
+# If the PDF file is the same as it was previously, then it didn't
+# pick up the change in the tex file, so fail.
+test.fail_test(pdf_output_1 == pdf_output_1a)
+
 
+# Change bib.
+test.write(['bibertest.tex'], sources_tex_content % "")
 test.write(['ref.bib'],sources_bib_content % '1982')
 
 test.run()
diff --git a/test/TEX/bibtex-latex-rerun.py b/test/TEX/bibtex-latex-rerun.py
index f0f8c34..7334f1e 100644
--- a/test/TEX/bibtex-latex-rerun.py
+++ b/test/TEX/bibtex-latex-rerun.py
@@ -47,14 +47,14 @@ env = Environment(tools=['pdftex', 'tex'])
 env.PDF( 'bibtest.tex' )
 """)
 
-test.write(['bibtest.tex'], r"""
+sources_tex_content = r"""
 \documentclass{article}
 \begin{document}
-Learn about cool math in \cite{koblitz:elliptic_curves}.
+Learn about %s cool math in \cite{koblitz:elliptic_curves}.
 \bibliographystyle{alpha}
 \bibliography{sources}
 \end{document}
-""")
+"""
 
 sources_bib_content = r"""
 @book{koblitz:elliptic_curves,
@@ -67,14 +67,24 @@ sources_bib_content = r"""
 
 
 
+test.write(['bibtest.tex'], sources_tex_content % "")
 test.write('sources.bib', sources_bib_content % '1981')
 
 test.run()
 
 pdf_output_1 = test.read('bibtest.pdf')
 
+# Change tex, but don't change bib. In this case, pdf should still be rebuilt.
+test.write(['bibtest.tex'], sources_tex_content % "really")
+test.run()
+pdf_output_1a = test.read('bibtest.pdf')
+# If the PDF file is the same as it was previously, then it didn't
+# pick up the change in the tex file, so fail.
+test.fail_test(pdf_output_1 == pdf_output_1a)
 
 
+# Change bib.
+test.write(['bibtest.tex'], sources_tex_content % "")
 test.write('sources.bib', sources_bib_content % '1982')
 
 test.run()
-- 
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