Libguestfs - Mar 2023 - [nbdkit PATCH 1/2] common/utils: document empty_vector compound literal assignment

I originally meant to post only the "vector.h" patch, but then
(independently) nbdkit wouldn't build. Hence the other (rust plugin)
patch.

Laszlo

Laszlo Ersek (2):
  common/utils: document empty_vector compound literal assignment
  plugins/rust: restrict predicates-{tree,core} to {1.0.7,1.0.5}

 common/utils/vector.h   | 8 +++++++-
 plugins/rust/Cargo.toml | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)


base-commit: 45b72f5bd8fc1b475fa130d06c86cd877bf595d5

We usually zero-initialize vectors like

  string_vector names = empty_vector;

Allocating and zeroing separately is frequently useful however. Document
the pattern

  string_vector names;
  names = (string_vector)empty_vector;

where "(string_vector)empty_vector" is a compound literal.

Link: http://mid.mail-archive.com/20230221183810.vjilfbmj3woqivlj at redhat.com
Suggested-by: Eric Blake <eblake at redhat.com>
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    I'll pick this patch to libnbd as well, once merged in nbdkit.
    
    context:-U10

 common/utils/vector.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/common/utils/vector.h b/common/utils/vector.h
index ac28c0b5363a..7337d26893eb 100644
--- a/common/utils/vector.h
+++ b/common/utils/vector.h
@@ -55,28 +55,34 @@
 /* Use of this macro defines a new type called ?name? containing an
  * extensible vector of ?type? elements.  For example:
  *
  *   DEFINE_VECTOR_TYPE (string_vector, char *);
  *
  * defines a new type called ?string_vector? as a vector of ?char *?.
  * You can create variables of this type:
  *
  *   string_vector names = empty_vector;
  *
+ * or
+ *
+ *   string_vector names;
+ *   names = (string_vector)empty_vector;
+ *
  * where ?names.ptr[]? will be an array of strings and ?names.len?
  * will be the number of strings.  There are no get/set accessors.  To
  * iterate over the strings you can use the ?.ptr? field directly:
  *
  *   for (size_t i = 0; i < names.len; ++i)
  *     printf ("%s\n", names.ptr[i]);
  *
- * Initializing with ?empty_vector? sets ?.ptr = NULL? and ?.len = 0?.
+ * Initializing with ?empty_vector?, or assigning the compound literal
+ * ?(string_vector)empty_vector?, sets ?.ptr = NULL? and ?.len = 0?.
  *
  * DEFINE_VECTOR_TYPE also defines utility functions.  For the full
  * list see the definition below, but useful functions include:
  *
  * ?name?_append  (eg. ?string_vector_append?)
  *   - Append a new element at the end.  This operation is cheap.
  *
  * ?name?_insert  (eg. ?string_vector_insert?)
  *   - Insert a new element at the beginning, middle or end.  This
  *     operation is more expensive because existing elements may need

The beautiful world of uncontained dependencies:

- We restrict mockall to 0.11.0, which in practice currently expands to
  0.11.4,

- mockall depends on predicates-tree,

- predicates-tree depends on predicates-core,

- approx. two weeks ago, predicates-tree and predicates-core have seen
  *PATCHLEVEL* upgrades (1.0.7 -> 1.0.9, and 1.0.5 -> 1.0.6, respectively)
  that now require "rustc 1.64.0 or newer".

RHEL-9.2 will eventually ship rustc 1.66, but RHEL-9.2 has not been
released. The above rustc requirement bump breaks the nbdkit build on
RHEL-9.1 -- which provides rustc 1.62. Restrict predicates-{tree,core} to
{1.0.7,1.0.5}.

(Side commentary: when such things can happen via a *patchlevel* upgrade,
that makes a total mockery of "semantic versioning"
<https://en.wikipedia.org/wiki/Software_versioning#Semantic_versioning>.)

Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 plugins/rust/Cargo.toml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/plugins/rust/Cargo.toml b/plugins/rust/Cargo.toml
index 45d8a755e6e3..64ed193a0008 100644
--- a/plugins/rust/Cargo.toml
+++ b/plugins/rust/Cargo.toml
@@ -29,6 +29,8 @@ errno = "0.2.5"
 lazy_static = "1.2.0"
 memoffset = "0.6.3"
 mockall = "0.11.0"
+predicates-core = "=1.0.5"
+predicates-tree = "=1.0.7"
 
 [[example]]
 name = "ramdisk"

On 3/28/23 18:25, Laszlo Ersek wrote:
> I originally meant to post only the "vector.h" patch, but then
> (independently) nbdkit wouldn't build. Hence the other (rust plugin)
> patch.
> 
> Laszlo
> 
> Laszlo Ersek (2):
>   common/utils: document empty_vector compound literal assignment
>   plugins/rust: restrict predicates-{tree,core} to {1.0.7,1.0.5}
> 
>  common/utils/vector.h   | 8 +++++++-
>  plugins/rust/Cargo.toml | 2 ++
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> 
> base-commit: 45b72f5bd8fc1b475fa130d06c86cd877bf595d5
Merged as commit range 45b72f5bd8fc..da7458d7071e.

Thanks,
Laszlo