Thanks everyone for your reviews. I believe I've addressed all review
comments, including the one from Elijah about the test failing with
sha256 (which turns out to be because I didn't add a call to
setup_git_directory(), which the other test helpers do).

Jonathan Tan (4):
  promisor-remote: read partialClone config here
  promisor-remote: support per-repository config
  run-command: move envvar-resetting function
  promisor-remote: teach lazy-fetch in any repo

 Makefile                      |   1 +
 cache.h                       |   1 -
 object-file.c                 |   7 +-
 promisor-remote.c             | 125 ++++++++++++++++++++--------------
 promisor-remote.h             |  28 +++++---
 repository.c                  |   6 ++
 repository.h                  |   4 ++
 run-command.c                 |  10 +++
 run-command.h                 |   9 +++
 setup.c                       |  10 ++-
 submodule.c                   |  14 +---
 t/helper/test-partial-clone.c |  43 ++++++++++++
 t/helper/test-tool.c          |   1 +
 t/helper/test-tool.h          |   1 +
 t/t0410-partial-clone.sh      |  23 +++++++
 15 files changed, 201 insertions(+), 82 deletions(-)
 create mode 100644 t/helper/test-partial-clone.c

Range-diff against v1:
1:  4a7ad9ffeb ! 1:  07290cba86 promisor-remote: read partialClone config here
    @@ promisor-remote.c: static int promisor_remote_config(const char *var, const char
      	const char *subkey;
      
     +	if (!strcmp(var, "extensions.partialclone")) {
    -+		repository_format_partial_clone = xstrdup(value);
    ++		/*
    ++		 * NULL value is handled in handle_extension_v0 in setup.c.
    ++		 */
    ++		if (value)
    ++			repository_format_partial_clone = xstrdup(value);
     +		return 0;
     +	}
     +
2:  d8f5fa9b9f ! 2:  c462927ff2 promisor-remote: support per-repository config
    @@ promisor-remote.c: static void promisor_remote_move_to_tail(struct promisor_remo
      	const char *name;
      	size_t namelen;
      	const char *subkey;
    - 
    - 	if (!strcmp(var, "extensions.partialclone")) {
    --		repository_format_partial_clone = xstrdup(value);
    -+		config->repository_format_partial_clone = xstrdup(value);
    +@@ promisor-remote.c: static int promisor_remote_config(const char *var, const char *value, void *data
    + 		 * NULL value is handled in handle_extension_v0 in setup.c.
    + 		 */
    + 		if (value)
    +-			repository_format_partial_clone = xstrdup(value);
    ++			config->repository_format_partial_clone = xstrdup(value);
      		return 0;
      	}
      
    @@ promisor-remote.c: static int promisor_remote_config(const char *var, const char
      }
      
     -static void promisor_remote_clear(void)
    -+static void promisor_remote_clear(struct promisor_remote_config *config)
    ++void promisor_remote_clear(struct promisor_remote_config *config)
      {
     -	while (promisors) {
     -		struct promisor_remote *r = promisors;
     -		promisors = promisors->next;
    ++	FREE_AND_NULL(config->repository_format_partial_clone);
    ++
     +	while (config->promisors) {
     +		struct promisor_remote *r = config->promisors;
     +		config->promisors = config->promisors->next;
    @@ promisor-remote.h: struct promisor_remote {
     +	repo_promisor_remote_reinit(the_repository);
     +}
     +
    ++void promisor_remote_clear(struct promisor_remote_config *config);
    ++
     +struct promisor_remote *repo_promisor_remote_find(struct repository *r, const char *remote_name);
     +static inline struct promisor_remote *promisor_remote_find(const char *remote_name)
     +{
    @@ promisor-remote.h: struct promisor_remote {
      /*
       * Fetches all requested objects from all promisor remotes, trying them one at
     
    + ## repository.c ##
    +@@
    + #include "lockfile.h"
    + #include "submodule-config.h"
    + #include "sparse-index.h"
    ++#include "promisor-remote.h"
    + 
    + /* The main repository */
    + static struct repository the_repo;
    +@@ repository.c: void repo_clear(struct repository *repo)
    + 		if (repo->index != &the_index)
    + 			FREE_AND_NULL(repo->index);
    + 	}
    ++
    ++	if (repo->promisor_remote_config) {
    ++		promisor_remote_clear(repo->promisor_remote_config);
    ++		FREE_AND_NULL(repo->promisor_remote_config);
    ++	}
    + }
    + 
    + int repo_read_index(struct repository *repo)
    +
      ## repository.h ##
     @@ repository.h: struct lock_file;
      struct pathspec;
3:  c5307a9f02 ! 3:  9cbdf60981 run-command: move envvar-resetting function
    @@ run-command.h: int run_processes_parallel_tr2(int n, get_next_task_fn, start_fai
      			       const char *tr2_category, const char *tr2_label);
      
     +/**
    -+ * Convenience function that adds entries to env_array that resets all
    -+ * repo-specific environment variables except for CONFIG_DATA_ENVIRONMENT. See
    -+ * local_repo_env in cache.h for more information.
    ++ * Convenience function which adds all GIT_* environment variables to env_array
    ++ * with the exception of GIT_CONFIG_PARAMETERS. When used as the env_array of a
    ++ * subprocess, these entries cause the corresponding environment variables to
    ++ * be unset in the subprocess. See local_repo_env in cache.h for more
    ++ * information.
     + */
     +void prepare_other_repo_env(struct strvec *env_array);
     +
4:  b70a00b9b0 ! 4:  5b41569ace promisor-remote: teach lazy-fetch in any repo
    @@ t/helper/test-partial-clone.c (new)
     +#include "repository.h"
     +#include "object-store.h"
     +
    ++/*
    ++ * Prints the size of the object corresponding to the given hash in a specific
    ++ * gitdir. This is similar to "git -C gitdir cat-file -s", except that this
    ++ * exercises the code that accesses the object of an arbitrary repository that
    ++ * is not the_repository. ("git -C gitdir" makes it so that the_repository is
    ++ * the one in gitdir.)
    ++ */
     +static void object_info(const char *gitdir, const char *oid_hex)
     +{
     +	struct repository r;
    @@ t/helper/test-partial-clone.c (new)
     +
     +int cmd__partial_clone(int argc, const char **argv)
     +{
    ++	setup_git_directory();
    ++
     +	if (argc < 4)
     +		die("too few arguments");
     +
    @@ t/t0410-partial-clone.sh: test_expect_success 'do not fetch when checking existe
     +test_expect_success 'lazy-fetch when accessing object not in the_repository' '
     +	rm -rf full partial.git &&
     +	test_create_repo full &&
    -+	printf 12345 >full/file.txt &&
    -+	git -C full add file.txt &&
    -+	git -C full commit -m "first commit" &&
    ++	test_commit -C full create-a-file file.txt &&
     +
     +	test_config -C full uploadpack.allowfilter 1 &&
     +	test_config -C full uploadpack.allowanysha1inwant 1 &&
     +	git clone --filter=blob:none --bare "file://$(pwd)/full" partial.git &&
    -+	FILE_HASH=$(git hash-object --stdin <full/file.txt) &&
    ++	FILE_HASH=$(git -C full rev-parse HEAD:file.txt) &&
     +
     +	# Sanity check that the file is missing
     +	git -C partial.git rev-list --objects --missing=print HEAD >out &&
     +	grep "[?]$FILE_HASH" out &&
     +
    -+	OUT=$(test-tool partial-clone object-info partial.git "$FILE_HASH") &&
    -+	test "$OUT" -eq 5 &&
    ++	git -C full cat-file -s "$FILE_HASH" >expect &&
    ++	test-tool partial-clone object-info partial.git "$FILE_HASH" >actual &&
    ++	test_cmp expect actual &&
     +
     +	# Sanity check that the file is now present
     +	git -C partial.git rev-list --objects --missing=print HEAD >out &&
-- 
2.32.0.rc1.229.g3e70b5a671-goog