commit-graph: simplify chunk writes into loop

In write_commit_graph_file() we now have one block of code filling the
array of 'struct chunk_info' with the IDs and sizes of chunks to be
written, and an other block of code calling the functions responsible
for writing individual chunks.  In case of optional chunks like Extra
Edge List an Base Graphs List there is also a condition checking
whether that chunk is necessary/desired, and that same condition is
repeated in both blocks of code. Other, newer chunks have similar
optional conditions.

Eliminate these repeated conditions by storing the function pointers
responsible for writing individual chunks in the 'struct chunk_info'
array as well, and calling them in a loop to write the commit-graph
file.  This will open up the possibility for a bit of foolproofing in
the following patch.

Helped-by: René Scharfe <l.s.r@web.de>
Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit-graph.c

@@ -1559,9 +1559,13 @@ static int write_graph_chunk_base(struct hashfile *f,
 	return 0;
 }
 
+typedef int (*chunk_write_fn)(struct hashfile *f,
+			      struct write_commit_graph_context *ctx);
+
 struct chunk_info {
 	uint32_t id;
 	uint64_t size;
+	chunk_write_fn write_fn;
 };
 
 static int write_commit_graph_file(struct write_commit_graph_context *ctx)
@@ -1624,27 +1628,34 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 
 	chunks[0].id = GRAPH_CHUNKID_OIDFANOUT;
 	chunks[0].size = GRAPH_FANOUT_SIZE;
+	chunks[0].write_fn = write_graph_chunk_fanout;
 	chunks[1].id = GRAPH_CHUNKID_OIDLOOKUP;
 	chunks[1].size = hashsz * ctx->commits.nr;
+	chunks[1].write_fn = write_graph_chunk_oids;
 	chunks[2].id = GRAPH_CHUNKID_DATA;
 	chunks[2].size = (hashsz + 16) * ctx->commits.nr;
+	chunks[2].write_fn = write_graph_chunk_data;
 	if (ctx->num_extra_edges) {
 		chunks[num_chunks].id = GRAPH_CHUNKID_EXTRAEDGES;
 		chunks[num_chunks].size = 4 * ctx->num_extra_edges;
+		chunks[num_chunks].write_fn = write_graph_chunk_extra_edges;
 		num_chunks++;
 	}
 	if (ctx->changed_paths) {
 		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMINDEXES;
 		chunks[num_chunks].size = sizeof(uint32_t) * ctx->commits.nr;
+		chunks[num_chunks].write_fn = write_graph_chunk_bloom_indexes;
 		num_chunks++;
 		chunks[num_chunks].id = GRAPH_CHUNKID_BLOOMDATA;
 		chunks[num_chunks].size = sizeof(uint32_t) * 3
 					  + ctx->total_bloom_filter_data_size;
+		chunks[num_chunks].write_fn = write_graph_chunk_bloom_data;
 		num_chunks++;
 	}
 	if (ctx->num_commit_graphs_after > 1) {
 		chunks[num_chunks].id = GRAPH_CHUNKID_BASE;
 		chunks[num_chunks].size = hashsz * (ctx->num_commit_graphs_after - 1);
+		chunks[num_chunks].write_fn = write_graph_chunk_base;
 		num_chunks++;
 	}
 
@@ -1680,19 +1691,12 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 			progress_title.buf,
 			num_chunks * ctx->commits.nr);
 	}
-	write_graph_chunk_fanout(f, ctx);
+
-	write_graph_chunk_oids(f, ctx);
+	for (i = 0; i < num_chunks; i++) {
-	write_graph_chunk_data(f, ctx);
+		if (chunks[i].write_fn(f, ctx))
-	if (ctx->num_extra_edges)
+			return -1;
-		write_graph_chunk_extra_edges(f, ctx);
-	if (ctx->changed_paths) {
-		write_graph_chunk_bloom_indexes(f, ctx);
-		write_graph_chunk_bloom_data(f, ctx);
-	}
-	if (ctx->num_commit_graphs_after > 1 &&
-	    write_graph_chunk_base(f, ctx)) {
-		return -1;
 	}
+
 	stop_progress(&ctx->progress);
 	strbuf_release(&progress_title);