merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 165 insertions, 9 deletions

diff --git a/third_party/git/diff.h b/third_party/git/diff.h
index c2c3056810..11de52e9e9 100644
--- a/third_party/git/diff.h
+++ b/third_party/git/diff.h
@@ -9,6 +9,49 @@
 #include "object.h"
 #include "oidset.h"
 
+/**
+ * The diff API is for programs that compare two sets of files (e.g. two trees,
+ * one tree and the index) and present the found difference in various ways.
+ * The calling program is responsible for feeding the API pairs of files, one
+ * from the "old" set and the corresponding one from "new" set, that are
+ * different.
+ * The library called through this API is called diffcore, and is responsible
+ * for two things.
+ *
+ * - finding total rewrites (`-B`), renames (`-M`) and copies (`-C`), and
+ * changes that touch a string (`-S`), as specified by the caller.
+ *
+ * - outputting the differences in various formats, as specified by the caller.
+ *
+ * Calling sequence
+ * ----------------
+ *
+ * - Prepare `struct diff_options` to record the set of diff options, and then
+ * call `repo_diff_setup()` to initialize this structure.  This sets up the
+ * vanilla default.
+ *
+ * - Fill in the options structure to specify desired output format, rename
+ * detection, etc.  `diff_opt_parse()` can be used to parse options given
+ * from the command line in a way consistent with existing git-diff family
+ * of programs.
+ *
+ * - Call `diff_setup_done()`; this inspects the options set up so far for
+ * internal consistency and make necessary tweaking to it (e.g. if textual
+ * patch output was asked, recursive behaviour is turned on); the callback
+ * set_default in diff_options can be used to tweak this more.
+ *
+ * - As you find different pairs of files, call `diff_change()` to feed
+ * modified files, `diff_addremove()` to feed created or deleted files, or
+ * `diff_unmerge()` to feed a file whose state is 'unmerged' to the API.
+ * These are thin wrappers to a lower-level `diff_queue()` function that is
+ * flexible enough to record any of these kinds of changes.
+ *
+ * - Once you finish feeding the pairs of files, call `diffcore_std()`.
+ * This will tell the diffcore library to go ahead and do its work.
+ *
+ * - Calling `diff_flush()` will produce the output.
+ */
+
 struct combine_diff_path;
 struct commit;
 struct diff_filespec;
@@ -65,21 +108,66 @@ typedef struct strbuf *(*diff_prefix_fn_t)(struct diff_options *opt, void *data)
 
 #define DIFF_FLAGS_INIT { 0 }
 struct diff_flags {
+
+	/**
+	 * Tells if tree traversal done by tree-diff should recursively descend
+	 * into a tree object pair that are different in preimage and postimage set.
+	 */
 	unsigned recursive;
 	unsigned tree_in_recursive;
+
+	/* Affects the way how a file that is seemingly binary is treated. */
 	unsigned binary;
 	unsigned text;
+
+	/**
+	 * Tells the patch output format not to use abbreviated object names on the
+	 * "index" lines.
+	 */
 	unsigned full_index;
+
+	/* Affects if diff-files shows removed files. */
 	unsigned silent_on_remove;
+
+	/**
+	 * Tells the diffcore library that the caller is feeding unchanged
+	 * filepairs to allow copies from unmodified files be detected.
+	 */
 	unsigned find_copies_harder;
+
 	unsigned follow_renames;
 	unsigned rename_empty;
+
+	/* Internal; used for optimization to see if there is any change. */
 	unsigned has_changes;
+
 	unsigned quick;
+
+	/**
+	 * Tells diff-files that the input is not tracked files but files in random
+	 * locations on the filesystem.
+	 */
 	unsigned no_index;
+
+	/**
+	 * Tells output routine that it is Ok to call user specified patch output
+	 * routine.  Plumbing disables this to ensure stable output.
+	 */
 	unsigned allow_external;
+
+	/**
+	 * For communication between the calling program and the options parser;
+	 * tell the calling program to signal the presence of difference using
+	 * program exit code.
+	 */
 	unsigned exit_with_status;
+
+	/**
+	 * Tells the library that the calling program is feeding the filepairs
+	 * reversed; `one` is two, and `two` is one.
+	 */
 	unsigned reverse_diff;
+
 	unsigned check_failed;
 	unsigned relative_name;
 	unsigned ignore_submodules;
@@ -131,36 +219,75 @@ enum diff_submodule_format {
 	DIFF_SUBMODULE_INLINE_DIFF
 };
 
+/**
+ * the set of options the calling program wants to affect the operation of
+ * diffcore library with.
+ */
 struct diff_options {
 	const char *orderfile;
+
+	/**
+	 * A constant string (can and typically does contain newlines to look for
+	 * a block of text, not just a single line) to filter out the filepairs
+	 * that do not change the number of strings contained in its preimage and
+	 * postimage of the diff_queue.
+	 */
 	const char *pickaxe;
+
 	const char *single_follow;
 	const char *a_prefix, *b_prefix;
 	const char *line_prefix;
 	size_t line_prefix_length;
+
+	/**
+	 * collection of boolean options that affects the operation, but some do
+	 * not have anything to do with the diffcore library.
+	 */
 	struct diff_flags flags;
 
 	/* diff-filter bits */
 	unsigned int filter;
 
 	int use_color;
+
+	/* Number of context lines to generate in patch output. */
 	int context;
+
 	int interhunkcontext;
+
+	/* Affects the way detection logic for complete rewrites, renames and
+	 * copies.
+	 */
 	int break_opt;
 	int detect_rename;
+
 	int irreversible_delete;
 	int skip_stat_unmatch;
 	int line_termination;
+
+	/* The output format used when `diff_flush()` is run. */
 	int output_format;
+
 	unsigned pickaxe_opts;
+
+	/* Affects the way detection logic for complete rewrites, renames and
+	 * copies.
+	 */
 	int rename_score;
 	int rename_limit;
+
 	int needed_rename_limit;
 	int degraded_cc_to_c;
 	int show_rename_progress;
 	int dirstat_permille;
 	int setup;
+
+	/* Number of hexdigits to abbreviate raw format output to. */
 	int abbrev;
+
+	/* If non-zero, then stop computing after this many changes. */
+	int max_changes;
+
 	int ita_invisible_in_index;
 /* white-space error highlighting */
 #define WSEH_NEW (1<<12)
@@ -192,6 +319,7 @@ struct diff_options {
 	/* to support internal diff recursion by --follow hack*/
 	int found_follow;
 
+	/* Callback which allows tweaking the options in diff_setup_done(). */
 	void (*set_default)(struct diff_options *);
 
 	FILE *file;
@@ -245,6 +373,22 @@ void diff_emit_submodule_error(struct diff_options *o, const char *err);
 void diff_emit_submodule_pipethrough(struct diff_options *o,
 				     const char *line, int len);
 
+struct diffstat_t {
+	int nr;
+	int alloc;
+	struct diffstat_file {
+		char *from_name;
+		char *name;
+		char *print_name;
+		const char *comments;
+		unsigned is_unmerged:1;
+		unsigned is_binary:1;
+		unsigned is_renamed:1;
+		unsigned is_interesting:1;
+		uintmax_t added, deleted;
+	} **files;
+};
+
 enum color_diff {
 	DIFF_RESET = 0,
 	DIFF_CONTEXT = 1,
@@ -270,6 +414,7 @@ enum color_diff {
 	DIFF_FILE_OLD_BOLD = 21,
 	DIFF_FILE_NEW_BOLD = 22,
 };
+
 const char *diff_get_color(int diff_use_color, enum color_diff ix);
 #define diff_get_color_opt(o, ix) \
 	diff_get_color((o)->use_color, ix)
@@ -284,11 +429,11 @@ struct combine_diff_path *diff_tree_paths(
 	struct combine_diff_path *p, const struct object_id *oid,
 	const struct object_id **parents_oid, int nparent,
 	struct strbuf *base, struct diff_options *opt);
-int diff_tree_oid(const struct object_id *old_oid,
-		  const struct object_id *new_oid,
-		  const char *base, struct diff_options *opt);
-int diff_root_tree_oid(const struct object_id *new_oid, const char *base,
-		       struct diff_options *opt);
+void diff_tree_oid(const struct object_id *old_oid,
+		   const struct object_id *new_oid,
+		   const char *base, struct diff_options *opt);
+void diff_root_tree_oid(const struct object_id *new_oid, const char *base,
+			struct diff_options *opt);
 
 struct combine_diff_path {
 	struct combine_diff_path *next;
@@ -307,11 +452,11 @@ struct combine_diff_path {
 		st_mult(sizeof(struct combine_diff_parent), (n)))
 
 void show_combined_diff(struct combine_diff_path *elem, int num_parent,
-			int dense, struct rev_info *);
+			struct rev_info *);
 
-void diff_tree_combined(const struct object_id *oid, const struct oid_array *parents, int dense, struct rev_info *rev);
+void diff_tree_combined(const struct object_id *oid, const struct oid_array *parents, struct rev_info *rev);
 
-void diff_tree_combined_merge(const struct commit *commit, int dense, struct rev_info *rev);
+void diff_tree_combined_merge(const struct commit *commit, struct rev_info *rev);
 
 void diff_set_mnemonic_prefix(struct diff_options *options, const char *a, const char *b);
 
@@ -334,6 +479,10 @@ void diff_change(struct diff_options *,
 
 struct diff_filepair *diff_unmerge(struct diff_options *, const char *path);
 
+void compute_diffstat(struct diff_options *options, struct diffstat_t *diffstat,
+		      struct diff_queue_struct *q);
+void free_diffstat_info(struct diffstat_t *diffstat);
+
 #define DIFF_SETUP_REVERSE      	1
 #define DIFF_SETUP_USE_SIZE_CACHE	4
 
@@ -438,7 +587,7 @@ int run_diff_index(struct rev_info *revs, int cached);
 
 int do_diff_cache(const struct object_id *, struct diff_options *);
 int diff_flush_patch_id(struct diff_options *, struct object_id *, int, int);
-void flush_one_hunk(struct object_id *, git_SHA_CTX *);
+void flush_one_hunk(struct object_id *result, git_hash_ctx *ctx);
 
 int diff_result_code(struct diff_options *, int);
 
@@ -450,6 +599,13 @@ int index_differs_from(struct repository *r, const char *def,
 		       int ita_invisible_in_index);
 
 /*
+ * Emit an interdiff of two object ID's to 'diff_options.file' optionally
+ * indented by 'indent' spaces.
+ */
+void show_interdiff(const struct object_id *, const struct object_id *,
+		    int indent, struct diff_options *);
+
+/*
  * Fill the contents of the filespec "df", respecting any textconv defined by
  * its userdiff driver.  The "driver" parameter must come from a
  * previous call to get_textconv(), and therefore should either be NULL or have