Handling of TIMESTAMP in html footer and header

In ITK: InsightSoftwareConsortium/ITK#5190  there has been a discussion about the use of `TIMESTAMP` in the html footer (and header) in respect to reproducibility (and creation of difference sets for documentation sites).
When the date is replaced by the actual value all the html files are involved. I the ITK project a html string was used and its value was replaced by means of a JavaScript function during the load of the html page.

This technique has now been implemented in doxygen as well.

Author: albert-github

src/htmlgen.cpp

@@ -122,6 +122,32 @@ static void writeServerSearchBox(TextStream &t,const QCString &relPath,bool high
   }
 }
 
+const char *replaceDatetime =  "<span class=\"datetime\"></span>;";
+const char *replaceDate     =  "<span class=\"date\"></span>;";
+const char *replaceTime     =  "<span class=\"time\"></span>;";
+const char *replaceYear     =  "<span class=\"year\"></span>;";
+static void writeBuildDateJS(TextStream &t)
+{
+  t << "$(function(){\n";
+      t << "let elements = document.getElementsByClassName(\"datetime\");\n";
+      t << "for (let i = 0; i < elements.length; i++) {\n";
+      t << "   elements.item(i).textContent = \"" << dateToString(DateTimeType::DateTime) << "\";\n";
+      t << "}\n";
+      t << "let elementsD= document.getElementsByClassName(\"date\");\n";
+      t << "for (let i = 0; i < elementsD.length; i++) {\n";
+      t << "   elementsD.item(i).textContent = \"" << dateToString(DateTimeType::Date) << "\";\n";
+      t << "}\n";
+      t << "let elementsT = document.getElementsByClassName(\"time\");\n";
+      t << "for (let i = 0; i < elementsT.length; i++) {\n";
+      t << "   elementsT.item(i).textContent = \"" << dateToString(DateTimeType::Time) << "\";\n";
+      t << "}\n";
+      t << "let elementsY = document.getElementsByClassName(\"year\");\n";
+      t << "for (let i = 0; i < elementsY.length; i++) {\n";
+      t << "   elementsY.item(i).textContent = \"" << yearToString() << "\";\n";
+      t << "}\n";
+  t << "});\n";
+}
+
 //------------------------------------------------------------------------
 /// Convert a set of LaTeX  commands `\(re)newcommand`  to a form readable by MathJax
 /// LaTeX syntax:
@@ -398,11 +424,11 @@ static QCString substituteHtmlKeywords(const QCString &file,
   {
     case TIMESTAMP_t::YES:
     case TIMESTAMP_t::DATETIME:
-      generatedBy = theTranslator->trGeneratedAt(dateToString(DateTimeType::DateTime),
+      generatedBy = theTranslator->trGeneratedAt(replaceDatetime,
                                                  convertToHtml(Config_getString(PROJECT_NAME)));
       break;
     case TIMESTAMP_t::DATE:
-      generatedBy = theTranslator->trGeneratedAt(dateToString(DateTimeType::Date),
+      generatedBy = theTranslator->trGeneratedAt(replaceDate,
                                                  convertToHtml(Config_getString(PROJECT_NAME)));
       break;
     case TIMESTAMP_t::NO:
@@ -592,6 +618,11 @@ static QCString substituteHtmlKeywords(const QCString &file,
   result = substituteKeywords(file,result,
   {
     // keyword           value getter
+    { "$datetime",       [&]() { return replaceDatetime; } },
+    { "$date",           [&]() { return replaceDate;     } },
+    { "$time",           [&]() { return replaceTime;     } },
+    { "$year",           [&]() { return replaceYear;     } },
+
     { "$navpath",        [&]() { return navPath;        } },
     { "$stylesheet",     [&]() { return cssFile;        } },
     { "$treeview",       [&]() { return treeViewCssJs;  } },
@@ -1286,6 +1317,15 @@ void HtmlGenerator::init()
       }
     }
   }
+
+  { 
+    std::ofstream f = Portable::openOutputStream(dname+"/build_date.js");
+    if (f.is_open())
+    {
+      TextStream t(&f);
+      writeBuildDateJS(t);
+    }
+  }
 }
 
 void HtmlGenerator::cleanup()

src/latexgen.cpp

@@ -871,6 +871,11 @@ static QCString substituteLatexKeywords(const QCString &file,
   result = substituteKeywords(file,result,
   {
     // keyword                     value getter
+    { "$datetime",                 [&]() { return dateToString(DateTimeType::DateTime);         } },
+    { "$date",                     [&]() { return dateToString(DateTimeType::Date);             } },
+    { "$time",                     [&]() { return dateToString(DateTimeType::Time);             } },
+    { "$year",                     [&]() { return yearToString();                               } },
+
     { "$latexdocumentpre",         [&]() { return theTranslator->latexDocumentPre();            } },
     { "$latexdocumentpost",        [&]() { return theTranslator->latexDocumentPost();           } },
     { "$generatedby",              [&]() { return generatedBy;                                  } },

src/util.cpp

@@ -3720,10 +3720,6 @@ QCString substituteKeywords(const QCString &file,const QCString &s,const QCStrin
   {
     // keyword          value getter
     { "$title",           [&]() { return !title.isEmpty() ? title : projName;       } },
-    { "$datetime",        [&]() { return dateToString(DateTimeType::DateTime);      } },
-    { "$date",            [&]() { return dateToString(DateTimeType::Date);          } },
-    { "$time",            [&]() { return dateToString(DateTimeType::Time);          } },
-    { "$year",            [&]() { return yearToString();                            } },
     { "$doxygenversion",  [&]() { return getDoxygenVersion();                       } },
     { "$projectname",     [&]() { return projName;                                  } },
     { "$projectnumber",   [&]() { return projNum;                                   } },

templates/html/header.html

@@ -16,6 +16,7 @@
 <!--END FULL_SIDEBAR-->
 <script type="text/javascript" src="$relpath^jquery.js"></script>
 <script type="text/javascript" src="$relpath^dynsections.js"></script>
+<script type="text/javascript" src="$relpath^build_date.js"></script>
 <!--BEGIN COPY_CLIPBOARD-->
 <script type="text/javascript" src="$relpath^clipboard.js"></script>
 <!--END COPY_CLIPBOARD-->