Added per-node 'is_precious' flag to indicate that outputs are precious.

Closes GH-25.

src/build.c

@@ -162,7 +162,10 @@ run_job(td_job_queue *queue, td_node *node, const char *line_prefix)
 
 	engine->stats.build_time += t2 - t1;
 
-	if (0 != result)
+	/* If the build failed, and the node isn't set to keep all its output files
+	 * in all possible cases (precious), then delete all output files as we
+	 * can't assume anything about their state. */
+	if (0 != result && 0 == (TD_NODE_PRECIOUS & node->flags))
 	{
 		pthread_mutex_unlock(&queue->mutex);
 		/* remove all output files */
@@ -171,7 +174,10 @@ run_job(td_job_queue *queue, td_node *node, const char *line_prefix)
 		pthread_mutex_lock(&queue->mutex);
 	}
 
-	/* mark all output files as dirty */
+	/* Mark all output files as dirty regardless of whether the build succeeded
+	 * or not. If it succeeded, we must assume the build overwrote them.
+	 * Otherwise, it's likely we've deleted them. In any case, touching them
+	 * again isn't going to hurt anything.*/
 	for (i = 0, count = node->output_count; i < count; ++i)
 		td_touch_file(node->outputs[i]);
 

src/engine.c

@@ -1015,6 +1015,13 @@ make_node(lua_State *L)
 	}
 	lua_pop(L, 1);
 
+	lua_getfield(L, 2, "is_precious");
+	if (lua_toboolean(L, -1))
+		node->flags = TD_NODE_PRECIOUS;
+	else
+		node->flags = 0;
+	lua_pop(L, 1);
+
 	node->deps = setup_deps(L, self, node, &node->dep_count);
 
 	setup_file_signers(L, self, node);
@@ -1245,6 +1252,10 @@ clean_file(td_engine *engine, td_node *node, td_file **dirs, int *dir_count, td_
 		dirs[index] = dir;
 	}
 
+	/* Don't delete the output of precious nodes. */
+	if (TD_NODE_PRECIOUS & node->flags)
+		return;
+
 	stat = td_stat_file(engine, file);
 
 	if (TD_STAT_EXISTS & stat->flags)

src/engine.h

@@ -142,6 +142,12 @@ typedef struct td_ancestor_data
 	time_t access_time;
 } td_ancestor_data;
 
+enum {
+	/* Don't delete node outputs on build error or when cleaning. Useful for
+	 * build jobs that take a very long time to run. */
+	TD_NODE_PRECIOUS = 1 << 0,
+};
+
 typedef struct td_node
 {
 	/* An annotation that should print when building this node.
@@ -182,6 +188,8 @@ typedef struct td_node
 	td_digest guid;
 	const td_ancestor_data *ancestor_data;
 
+	int flags;
+
 	td_job job;
 } td_node;