merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/commit-slab.h

@@ -0,0 +1,51 @@
+#ifndef COMMIT_SLAB_H
+#define COMMIT_SLAB_H
+
+#include "commit-slab-decl.h"
+#include "commit-slab-impl.h"
+
+/*
+ * define_commit_slab(slabname, elemtype) creates boilerplate code to define
+ * a new struct (struct slabname) that is used to associate a piece of data
+ * of elemtype to commits, and a few functions to use that struct.
+ *
+ * After including this header file, using:
+ *
+ * define_commit_slab(indegree, int);
+ *
+ * will let you call the following functions:
+ *
+ * - int *indegree_at(struct indegree *, struct commit *);
+ *
+ *   This function locates the data associated with the given commit in
+ *   the indegree slab, and returns the pointer to it.  The location to
+ *   store the data is allocated as necessary.
+ *
+ * - int *indegree_peek(struct indegree *, struct commit *);
+ *
+ *   This function is similar to indegree_at(), but it will return NULL
+ *   until a call to indegree_at() was made for the commit.
+ *
+ * - void init_indegree(struct indegree *);
+ *   void init_indegree_with_stride(struct indegree *, int);
+ *
+ *   Initializes the indegree slab that associates an array of integers
+ *   to each commit. 'stride' specifies how big each array is.  The slab
+ *   that is initialized by the variant without "_with_stride" associates
+ *   each commit with an array of one integer.
+ *
+ * - void clear_indegree(struct indegree *);
+ *
+ *   Empties the slab.  The slab can be reused with the same stride
+ *   without calling init_indegree() again or can be reconfigured to a
+ *   different stride by calling init_indegree_with_stride().
+ *
+ *   Call this function before the slab falls out of scope to avoid
+ *   leaking memory.
+ */
+
+#define define_commit_slab(slabname, elemtype) \
+	declare_commit_slab(slabname, elemtype); \
+	implement_static_commit_slab(slabname, elemtype)
+
+#endif /* COMMIT_SLAB_H */