Prepare for change of VAR_ARGS value

Change-Id: I0b1955bb660b5e19587799de657c63634705b99c

3 files changed, 16 insertions, 6 deletions

diff --git a/include/formula/funcvarargs.h b/include/formula/funcvarargs.h
index c0836a55a1e4..1be68692fe41 100644
--- a/include/formula/funcvarargs.h
+++ b/include/formula/funcvarargs.h
@@ -22,6 +22,9 @@
     reportdesign/source/ui/misc/FunctionHelper.cxx
     FunctionDescription::getVarArgsStart() has to provide some backward
     compatibility for implicit API stability.
+    The new VAR_ARGS value must be significantly greater than the old
+    PAIRED_VAR_ARGS (2*VAR_ARGS) value, in fact greater than any used number of
+    fixed parameters followed by optional paired parameters.
 
     @NOTE: also
     reportbuilder/java/org/libreoffice/report/pentaho/StarFunctionDescription.java
diff --git a/reportbuilder/java/org/libreoffice/report/pentaho/StarFunctionDescription.java b/reportbuilder/java/org/libreoffice/report/pentaho/StarFunctionDescription.java
index b743ae08e4a1..96c4346e9989 100644
--- a/reportbuilder/java/org/libreoffice/report/pentaho/StarFunctionDescription.java
+++ b/reportbuilder/java/org/libreoffice/report/pentaho/StarFunctionDescription.java
@@ -152,6 +152,7 @@ public final class StarFunctionDescription extends WeakBase
         final boolean infinite = functionDescription.isInfiniteParameterCount();
         if (infinite)
         {
+            // Identical value as VAR_ARGS from formula/funcvarargs.h
             count = 30;
         }
         final FunctionArgument[] args = new FunctionArgument[count];
diff --git a/reportdesign/source/ui/misc/FunctionHelper.cxx b/reportdesign/source/ui/misc/FunctionHelper.cxx
index 584a0288e4aa..349bc8d48061 100644
--- a/reportdesign/source/ui/misc/FunctionHelper.cxx
+++ b/reportdesign/source/ui/misc/FunctionHelper.cxx
@@ -20,6 +20,7 @@
 #include "FunctionHelper.hxx"
 
 #include <osl/diagnose.h>
+#include <formula/funcvarargs.h>
 
 
 namespace rptui
@@ -211,13 +212,18 @@ sal_uInt32 FunctionDescription::getVarArgsStart() const
     // Don't use defines/constants that could change in future, parameter count
     // could be part of an implicit stable API.
     // offapi/com/sun/star/report/meta/XFunctionDescription.idl doesn't tell.
-    const sal_uInt32 nVarArgs = 30;         // ugly hard coded VAR_ARGS of formula::ParaWin
-    const sal_uInt32 nPairedVarArgs = 60;   // ugly hard coded PAIRED_VAR_ARGS of formula::ParaWin
+    const sal_uInt32 nVarArgs30 = 30;         // ugly hard coded VAR_ARGS of formula::ParaWin
+    const sal_uInt32 nPairedVarArgs60 = 60;   // ugly hard coded PAIRED_VAR_ARGS of formula::ParaWin
     sal_uInt32 nLen = m_aParameter.getLength();
-    if (nLen >= nPairedVarArgs)
-        nLen -= nPairedVarArgs;
-    else if (nLen >= nVarArgs)
-        nLen -= nVarArgs;
+    // If the value of VAR_ARGS changes then adapt *and* maintain implicit API
+    // stability, ie. old code using the old VAR_ARGS and PAIRED_VAR_ARGS
+    // values must still be handled. It is *not* sufficient to simply change
+    // the values here.
+    static_assert(nVarArgs30 == VAR_ARGS && nPairedVarArgs60 == PAIRED_VAR_ARGS);
+    if (nLen >= nPairedVarArgs60)
+        nLen -= nPairedVarArgs60;
+    else if (nLen >= nVarArgs30)
+        nLen -= nVarArgs30;
     return nLen ? nLen - 1 : 0;
 }