sh-quote, execute, spawn-pipe, etc.: Make better use of 'const'

[Bruno Haible]

The execute, spawn-pipe, etc. functions so far take a 'char **' for
an array of strings to pass as arguments to a subprocess. This is
suboptimal, because it requires casts from 'const char *' to 'char *'
in many places.

It is better to make clear through the types that the arguments strings
are not being written to. This removes the need to cast from 'const char *'
to 'char *'. It introduces the need to cast from 'const char **' to 'char **',
but in much fewer places. Since a cast from 'const char **' to 'char **'
does not violate strict aliasing rules (ISO C 11 § 6.5.(7)), this is OK.

IMO POSIX doesn't get this right in the functions execv(), posix_spawn(),
iconv() etc.


2020-12-11  Bruno Haible  <bruno@clisp.org>

        sh-quote, execute, spawn-pipe, etc.: Make better use of 'const'.
        * lib/sh-quote.h (shell_quote_argv): Does not need write access to the
        elements of argv.
        * lib/sh-quote.c (shell_quote_argv): Likewise.
        * lib/windows-spawn.h (prepare_spawn): Add 'const' the argument type and
        the return type.
        * lib/windows-spawn.c (prepare_spawn): Likewise.
        * lib/os2-spawn.h (prepare_spawn): Likewise.
        * lib/os2-spawn.c (prepare_spawn): Likewise.
        * lib/execute.h (execute): Does not need write access to the elements of
        prog_argv.
        * lib/execute.c (execute): Likewise.
        * lib/spawn-pipe.h (create_pipe_out, create_pipe_in, create_pipe_bidi):
        Likewise.
        * lib/spawn-pipe.c (create_pipe, create_pipe_bidi, create_pipe_in,
        create_pipe_out): Likewise.
        * lib/pipe-filter.h (pipe_filter_ii_execute, pipe_filter_gi_create):
        Likewise.
        * lib/pipe-filter-ii.c (pipe_filter_ii_execute): Likewise.
        * lib/pipe-filter-gi.c (pipe_filter_gi_create): Likewise.
        * lib/javaexec.h (execute_fn): Does not need write access to the
        elements of prog_argv.
        * lib/javaexec.c (execute_java_class): Update variable types and remove
        casts to 'char *'.
        * lib/csharpexec.h (execute_fn): Does not need write access to the
        elements of prog_argv.
        * lib/csharpexec.c (execute_csharp_using_mono,
        execute_csharp_using_sscli): Update variable types and remove casts to
        'char *'.
        * lib/javacomp.c (compile_using_envjavac, compile_using_gcj,
        compile_using_javac, compile_using_jikes, is_envjavac_gcj,
        is_envjavac_gcj43, is_gcj_present, is_gcj_43, is_javac_present,
        is_jikes_present): Update variable types and remove casts to 'char *'.
        * lib/javaversion.c (execute_and_read_line): Does not need write access
        to the elements of prog_argv.
        * lib/csharpcomp.c (compile_csharp_using_mono,
        compile_csharp_using_sscli): Update variable types and remove casts to
        'char *'.
        * tests/test-sh-quote.c (main): Update variable types and remove casts
        to 'char *'.
        * tests/test-execute-main.c (main): Update variable types and remove
        casts to 'char *'.
        * tests/test-spawn-pipe-main.c (test_pipe): Update variable types and
        remove casts to 'char *'.
        * NEWS: Mention the changes.

diff --git a/NEWS b/NEWS
index 747165a..f484881 100644
--- a/NEWS
+++ b/NEWS
@@ -60,6 +60,39 @@ User visible incompatible changes
 
 Date        Modules         Changes
 
+2020-12-11  sh-quote        The argv argument of the 'shell_quote_argv' 
function
+                            is now of type 'const char * const *'.  You no
+                            longer need to cast read-only strings to 'char *'
+                            when constructing this argument.
+            execute         The prog_argv argument of the 'execute' function
+                            is now of type 'const char * const *'.  You no
+                            longer need to cast read-only strings to 'char *'
+                            when constructing this argument.
+            spawn-pipe      The prog_argv argument of the functions
+                            'create_pipe_out', 'create_pipe_in',
+                            'create_pipe_bidi' is now of type
+                            'const char * const *'.  You no longer need to cast
+                            read-only strings to 'char *' when constructing 
this
+                            argument.
+            pipe-filter-gi  The prog_argv argument of the
+                            'pipe_filter_gi_create' function is now of type
+                            'const char * const *'.  You no longer need to cast
+                            read-only strings to 'char *' when constructing 
this
+                            argument.
+            pipe-filter-ii  The prog_argv argument of the
+                            'pipe_filter_ii_execute' function is now of type
+                            'const char * const *'.  You no longer need to cast
+                            read-only strings to 'char *' when constructing 
this
+                            argument.
+            javaexec        The prog_argv argument of the 'execute_fn' function
+                            type is now of type 'const char * const *'.  Update
+                            the signature of all your implementations of this
+                            type.
+            csharpexec      The prog_argv argument of the 'execute_fn' function
+                            type is now of type 'const char * const *'.  Update
+                            the signature of all your implementations of this
+                            type.
+
 2020-12-02  spawn-pipe      The functions 'create_pipe_out', 'create_pipe_in',
                             'create_pipe_bidi' now take a 4th argument
                             'const char *directory'. To maintain the previous

0001-sh-quote-execute-spawn-pipe-etc.-Make-better-use-of-.patch
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