Speedup OpamSystem.read by using Stdlib.In_channel.input_all when available

Author: kit-ty-kate

master_changes.md

@@ -180,3 +180,4 @@ users)
 
 ## opam-core
   * `OpamStd.Env`: add `env_string_list` for parsing string list environment variables (comma separated) [#5682 @desumn]
+  * `OpamSystem.read`: Speedup by using `Stdlib.In_channel.input_all` when available [#5896 @kit-ty-kate]

src/core/dune

@@ -27,6 +27,13 @@
   (write-file opamVersionInfo.ml
               "let version = \"%{read-strings:version}\""))
 
+(rule
+  (enabled_if (>= %{ocaml_version} "4.14"))
+  (action (copy opamCompatInChannel.real.ml opamCompatInChannel.ml)))
+(rule
+  (enabled_if (< %{ocaml_version} "4.14"))
+  (action (copy opamCompatInChannel.compat.ml opamCompatInChannel.ml)))
+
 (rule
   (targets version)
   (deps    ../../shell/get_version.ml ../../configure.ac)

src/core/opamCompatInChannel.compat.ml

@@ -0,0 +1,24 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright 2024 Kate Deplaix                                         *)
+(*                                                                        *)
+(*  All rights reserved. This file is distributed under the terms of the  *)
+(*  GNU Lesser General Public License version 2.1, with the special       *)
+(*  exception on linking described in the file LICENSE.                   *)
+(*                                                                        *)
+(**************************************************************************)
+
+let input_all ic =
+  let n = 32768 in
+  let s = Bytes.create n in
+  let b = Buffer.create 1024 in
+  let rec iter ic b s =
+    let nread =
+      try input ic s 0 n
+      with End_of_file -> 0 in
+    if nread > 0 then (
+      Buffer.add_subbytes b s 0 nread;
+      iter ic b s
+    ) in
+  iter ic b s;
+  Buffer.contents b

src/core/opamCompatInChannel.mli

@@ -0,0 +1,14 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright 2024 Kate Deplaix                                         *)
+(*                                                                        *)
+(*  All rights reserved. This file is distributed under the terms of the  *)
+(*  GNU Lesser General Public License version 2.1, with the special       *)
+(*  exception on linking described in the file LICENSE.                   *)
+(*                                                                        *)
+(**************************************************************************)
+
+(** Compatibility module for Stdlib.In_channel which was added in OCaml 4.14 *)
+
+(** Emulates or aliases [Stdlib.In_channel.input_all] *)
+val input_all : Stdlib.in_channel -> string

src/core/opamCompatInChannel.real.ml

@@ -0,0 +1,11 @@
+(**************************************************************************)
+(*                                                                        *)
+(*    Copyright 2024 Kate Deplaix                                         *)
+(*                                                                        *)
+(*  All rights reserved. This file is distributed under the terms of the  *)
+(*  GNU Lesser General Public License version 2.1, with the special       *)
+(*  exception on linking described in the file LICENSE.                   *)
+(*                                                                        *)
+(**************************************************************************)
+
+include Stdlib.In_channel

src/core/opamSystem.ml

@@ -221,20 +221,7 @@ let remove_file file =
       internal_error "Cannot remove %s (%s)." file (Printexc.to_string e)
   )
 
-let string_of_channel ic =
-  let n = 32768 in
-  let s = Bytes.create n in
-  let b = Buffer.create 1024 in
-  let rec iter ic b s =
-    let nread =
-      try input ic s 0 n
-      with End_of_file -> 0 in
-    if nread > 0 then (
-      Buffer.add_subbytes b s 0 nread;
-      iter ic b s
-    ) in
-  iter ic b s;
-  Buffer.contents b
+let string_of_channel = OpamCompatInChannel.input_all
 
 let read file =
   let ic =