plumbing: commitgraph, fix types and handle commit-graph-chains

Unfortunately the original variant makes some incorrect typing
assumptions about commit-graphs which make handling graph chains
difficult to do correctly. This creates a new subpackage and deprecates
the old one. It then adds support commit graph chains.

Signed-off-by: Andrew Thornton <art27@cantab.net>

1 files changed, 58 insertions, 55 deletions

diff --git a/plumbing/format/commitgraph/doc.go b/plumbing/format/commitgraph/doc.go
index 41cd8b1..c320e18 100644
--- a/plumbing/format/commitgraph/doc.go
+++ b/plumbing/format/commitgraph/doc.go
@@ -1,23 +1,26 @@
 // Package commitgraph implements encoding and decoding of commit-graph files.
 //
+// Deprecated: This package uses the wrong types for Generation and Index in CommitData.
+// Use the v2 package instead.
+//
 // Git commit graph format
 // =======================
 //
 // The Git commit graph stores a list of commit OIDs and some associated
 // metadata, including:
 //
-// - The generation number of the commit. Commits with no parents have
-//   generation number 1; commits with parents have generation number
-//   one more than the maximum generation number of its parents. We
-//   reserve zero as special, and can be used to mark a generation
-//   number invalid or as "not computed".
+//   - The generation number of the commit. Commits with no parents have
+//     generation number 1; commits with parents have generation number
+//     one more than the maximum generation number of its parents. We
+//     reserve zero as special, and can be used to mark a generation
+//     number invalid or as "not computed".
 //
 // - The root tree OID.
 //
 // - The commit date.
 //
-// - The parents of the commit, stored using positional references within
-//   the graph file.
+//   - The parents of the commit, stored using positional references within
+//     the graph file.
 //
 // These positional references are stored as unsigned 32-bit integers
 // corresponding to the array position within the list of commit OIDs. Due
@@ -35,68 +38,68 @@
 //
 // HEADER:
 //
-//   4-byte signature:
-//       The signature is: {'C', 'G', 'P', 'H'}
+//	4-byte signature:
+//	    The signature is: {'C', 'G', 'P', 'H'}
 //
-//   1-byte version number:
-//       Currently, the only valid version is 1.
+//	1-byte version number:
+//	    Currently, the only valid version is 1.
 //
-//   1-byte Hash Version (1 = SHA-1)
-//       We infer the hash length (H) from this value.
+//	1-byte Hash Version (1 = SHA-1)
+//	    We infer the hash length (H) from this value.
 //
-//   1-byte number (C) of "chunks"
+//	1-byte number (C) of "chunks"
 //
-//   1-byte (reserved for later use)
-//      Current clients should ignore this value.
+//	1-byte (reserved for later use)
+//	   Current clients should ignore this value.
 //
 // CHUNK LOOKUP:
 //
-//   (C + 1) * 12 bytes listing the table of contents for the chunks:
-//       First 4 bytes describe the chunk id. Value 0 is a terminating label.
-//       Other 8 bytes provide the byte-offset in current file for chunk to
-//       start. (Chunks are ordered contiguously in the file, so you can infer
-//       the length using the next chunk position if necessary.) Each chunk
-//       ID appears at most once.
+//	(C + 1) * 12 bytes listing the table of contents for the chunks:
+//	    First 4 bytes describe the chunk id. Value 0 is a terminating label.
+//	    Other 8 bytes provide the byte-offset in current file for chunk to
+//	    start. (Chunks are ordered contiguously in the file, so you can infer
+//	    the length using the next chunk position if necessary.) Each chunk
+//	    ID appears at most once.
 //
-//   The remaining data in the body is described one chunk at a time, and
-//   these chunks may be given in any order. Chunks are required unless
-//   otherwise specified.
+//	The remaining data in the body is described one chunk at a time, and
+//	these chunks may be given in any order. Chunks are required unless
+//	otherwise specified.
 //
 // CHUNK DATA:
 //
-//   OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
-//       The ith entry, F[i], stores the number of OIDs with first
-//       byte at most i. Thus F[255] stores the total
-//       number of commits (N).
-//
-//   OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
-//       The OIDs for all commits in the graph, sorted in ascending order.
-//
-//   Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
-//     * The first H bytes are for the OID of the root tree.
-//     * The next 8 bytes are for the positions of the first two parents
-//       of the ith commit. Stores value 0x7000000 if no parent in that
-//       position. If there are more than two parents, the second value
-//       has its most-significant bit on and the other bits store an array
-//       position into the Extra Edge List chunk.
-//     * The next 8 bytes store the generation number of the commit and
-//       the commit time in seconds since EPOCH. The generation number
-//       uses the higher 30 bits of the first 4 bytes, while the commit
-//       time uses the 32 bits of the second 4 bytes, along with the lowest
-//       2 bits of the lowest byte, storing the 33rd and 34th bit of the
-//       commit time.
-//
-//   Extra Edge List (ID: {'E', 'D', 'G', 'E'}) [Optional]
-//       This list of 4-byte values store the second through nth parents for
-//       all octopus merges. The second parent value in the commit data stores
-//       an array position within this list along with the most-significant bit
-//       on. Starting at that array position, iterate through this list of commit
-//       positions for the parents until reaching a value with the most-significant
-//       bit on. The other bits correspond to the position of the last parent.
+//	OID Fanout (ID: {'O', 'I', 'D', 'F'}) (256 * 4 bytes)
+//	    The ith entry, F[i], stores the number of OIDs with first
+//	    byte at most i. Thus F[255] stores the total
+//	    number of commits (N).
+//
+//	OID Lookup (ID: {'O', 'I', 'D', 'L'}) (N * H bytes)
+//	    The OIDs for all commits in the graph, sorted in ascending order.
+//
+//	Commit Data (ID: {'C', 'D', 'A', 'T' }) (N * (H + 16) bytes)
+//	  * The first H bytes are for the OID of the root tree.
+//	  * The next 8 bytes are for the positions of the first two parents
+//	    of the ith commit. Stores value 0x7000000 if no parent in that
+//	    position. If there are more than two parents, the second value
+//	    has its most-significant bit on and the other bits store an array
+//	    position into the Extra Edge List chunk.
+//	  * The next 8 bytes store the generation number of the commit and
+//	    the commit time in seconds since EPOCH. The generation number
+//	    uses the higher 30 bits of the first 4 bytes, while the commit
+//	    time uses the 32 bits of the second 4 bytes, along with the lowest
+//	    2 bits of the lowest byte, storing the 33rd and 34th bit of the
+//	    commit time.
+//
+//	Extra Edge List (ID: {'E', 'D', 'G', 'E'}) [Optional]
+//	    This list of 4-byte values store the second through nth parents for
+//	    all octopus merges. The second parent value in the commit data stores
+//	    an array position within this list along with the most-significant bit
+//	    on. Starting at that array position, iterate through this list of commit
+//	    positions for the parents until reaching a value with the most-significant
+//	    bit on. The other bits correspond to the position of the last parent.
 //
 // TRAILER:
 //
-// 	H-byte HASH-checksum of all of the above.
+//	H-byte HASH-checksum of all of the above.
 //
 // Source:
 // https://raw.githubusercontent.com/git/git/master/Documentation/technical/commit-graph-format.txt