SVN Code merging between multiple branches problems

Question

We use SVN 1.6 We like to perform code merging between branches and we are in a dilemma situation.

Branch A exists
Folks making code changes on Branch A
Branch B created from branch A
Folks making code changes on both branches A and B
Branch A sync code merging to Branch B
After some time
Branch C created from branch A
Branch A continues sync code merging to Branch B (for a short time)
Folks making code changes on Branch C Folks stop code changes on Branch A and branch "frozen", no more ci
Folks making code changes on Branch B
Branch C sync code merging to Branch B
Folks making code changes on Branches B and C
After some long period of time

Now Dilemma: We like to merge Branch B to Branch C

Because Branch B is from Branch A and not Branch C, we could not apply --reintegrate option for code merging from B to C because they don't share common ancestry

What's the least risky way to merge (without the --reintegrate option) to prevent "double merges/duplicated code" of (C in B) into branch C ?

Answer 1

Visualize your branch structure by a simple drawing. My understanding of your problem is:

               C ---- C ---- C ----- C
              /        \      \
A --- A ---- A --- A    \      \      ???
 \     \      \     \    \      \
  B --- B ---- B --- B -- B ---- B ---- B

I would integrate C and B in A. If that is not an option you could do it in 3 steps / 3 series of steps:

1. Merge all changes done in B into C but not those merged from A. Do this until you reach the last merge from A to B (which is not in C)
2. Merge this last merge from A to B also into C
3. Merge the remaining changes made on B (after the last merge from A), but leave out the changes included from C

I am not completely clear about your structure. If it would be

               C ---- C ---- C ----- C
              /        \      \
A --- A ---- A --- A    \      \      ???
 \     \            \    \      \
  B --- B ---- B --- B -- B ---- B ---- B

I would take the last changes from A directly into C.