Do not hardcode "/bin/sh" in compile. Bug#24338, Bug#29723

* doc/emacs/custom.texi (Connection Variables): New node.

* doc/emacs/emacs.texi (Top): Add entry for Connection Variables.

* doc/emacs/misc.texi (Single Shell): Mention default value for
remote buffers.

* doc/lispref/variables.texi (Connection Local Variables):
Describe `with-connection-local-variables' instead of
`with-connection-local-profiles'.

* doc/misc/tramp.texi (Remote processes): Refer to Emacs manual.
Mention default connection-local settings for `shell-file-name'
and `shell-command-switch'.

* etc/NEWS: Mention connection-local variables changes.

* lisp/files-x.el (hack-connection-local-variables):
Push connection-local variables to `file-local-variables-alist'.
(connection-local-criteria-for-default-directory): New defsubst.
(with-connection-local-variables): Rename from
`with-connection-local-profiles'.  Adapt implementation.

* lisp/files.el (hack-local-variables):
Call `hack-connection-local-variables'.

* lisp/shell.el (shell): Use `with-connection-local-variables'.

* lisp/subr.el (start-file-process-shell-command):
* lisp/progmodes/compile.el (compilation-start):
Use `with-connection-local-variables'.  Do not set "/bin/sh" for
remote buffers, trust settings of `shell-file-name'.  (Bug#24338),
(Bug#29723)

* lisp/net/ange-ftp.el (ange-ftp-compress, ange-ftp-uncompress):
Use `shell-command-switch'.

* lisp/net/tramp-adb.el (tramp-adb-connection-local-default-profile):
New defvar.  Add it to connection-local profiles after loading "shell".

* lisp/net/tramp-integration.el (tramp-compat): Require tramp-compat.
(tramp-compat-exec-path): Do not declare anymore.
(tramp-connection-local-safe-shell-file-names): New defvar.
(tramp-connection-local-default-profile): New defconst.  Activate
it after loading "shell".
(shell-file-name, shell-command-switch): Add safe-local-variable
property.

* lisp/net/tramp-sh.el (tramp-display-escape-sequence-regexp):
Add tramp-autoload cookie.

* test/lisp/files-x-tests.el (remote-shell-file-name):
Add safe-local-variable property to remote-* variables.
(tramp-connection-local-default-profile): Declare.
(files-x-test-with-connection-local-variables):
Rename from `files-x-test-with-connection-local-profiles'.  Adapt
implementation.

* test/lisp/net/tramp-tests.el
(tramp-test34-connection-local-variables): New test.
(tramp-test34-explicit-shell-file-name): Run it also for tramp-adb.
Bind connection-local-{profile,criteria}-alist.  Use tramp-adb
specific `shell-file-name'.  Add safe-local-variable property to
`explicit-shell-file-name' and `explicit-sh-args'.

5 files changed, 75 insertions, 6 deletions

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index 474149fcae6..c649c170293 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -765,6 +765,8 @@ expects (@pxref{Examining}).
 * Locals::              Per-buffer values of variables.
 * File Variables::      How files can specify variable values.
 * Directory Variables:: How variable values can be specified by directory.
+* Connection Variables:: Variables which are valid for buffers with a
+                           remote default directory.
 @end menu
 
 @node Examining
@@ -1421,6 +1423,52 @@ variables are handled in the same way as unsafe file-local variables
 do not visit a file directly but perform work within a directory, such
 as Dired buffers (@pxref{Dired}).
 
+@node Connection Variables
+@subsection Per-Connection Local Variables
+@cindex local variables, for all remote connections
+@cindex connection-local variables
+@cindex per-connection local variables
+
+  Most of the variables reflect the situation on the local machine.
+Often, they must use a different value when you operate in buffers
+with a remote default directory.  Think about the shell to be applied
+when calling @code{shell} -- it might be @file{/bin/bash} on your
+local machine, and @file{/bin/ksh} on a remote machine.
+
+  This can be accomplished with @dfn{connection-local variables}.
+Directory and file local variables override connection-local
+variables.  Unsafe connection-local variables are handled in the same
+way as unsafe file-local variables (@pxref{Safe File Variables}).
+
+@findex connection-local-set-profile-variables
+@findex connection-local-set-profiles
+  Connection-local variables are declared as a group of
+variables/value pairs in a @dfn{profile}, using the
+@code{connection-local-set-profile-variables} function.  The function
+@code{connection-local-set-profiles} activates profiles for a given
+criteria, identifying a remote machine:
+
+@example
+(connection-local-set-profile-variables 'remote-ksh
+   '((shell-file-name . "/bin/ksh")
+     (shell-command-switch . "-c")))
+
+(connection-local-set-profile-variables 'remote-bash
+   '((shell-file-name . "/bin/bash")
+     (shell-command-switch . "-c")))
+
+(connection-local-set-profiles
+   '(:application tramp :machine "remotemachine") 'remote-ksh)
+@end example
+
+  This code declares two different profiles, @code{remote-ksh} and
+@code{remote-bash}. The profile @code{remote-ksh} is applied to all
+buffers which have a remote default directory matching the regexp
+@code{"remotemachine} as host name.  Such a criteria can also
+discriminate for the properties @code{:protocol} (this is the Tramp
+method) or @code{:user} (a remote user name).  The @code{nil} criteria
+matches all buffers with a remote default directory.
+
 @node Key Bindings
 @section Customizing Key Bindings
 @cindex key bindings
diff --git a/doc/emacs/emacs.texi b/doc/emacs/emacs.texi
index 950ddc01123..7edc1a5fae1 100644
--- a/doc/emacs/emacs.texi
+++ b/doc/emacs/emacs.texi
@@ -1135,6 +1135,8 @@ Variables
 * Locals::              Per-buffer values of variables.
 * File Variables::      How files can specify variable values.
 * Directory Variables:: How variable values can be specified by directory.
+* Connection Variables:: Variables which are valid for buffers with a
+                           remote default directory.
 
 Local Variables in Files
 
diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index a3aa71e2672..7d7065a441a 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -795,6 +795,10 @@ to @command{gpg}.  This will output the list of keys to the
 name is relative, Emacs searches the directories listed in
 @code{exec-path} (@pxref{Shell}).
 
+  If the default directory is remote (@pxref{Remote Files}), the
+default value is @file{/bin/sh}.  This can be changed by declaring
+@code{shell-file-name} connection-local (@pxref{Connection Variables}).
+
   To specify a coding system for @kbd{M-!} or @kbd{M-|}, use the command
 @kbd{C-x @key{RET} c} immediately beforehand.  @xref{Communication Coding}.
 
diff --git a/doc/lispref/variables.texi b/doc/lispref/variables.texi
index f1e0e37e6d6..aca7d2f5e93 100644
--- a/doc/lispref/variables.texi
+++ b/doc/lispref/variables.texi
@@ -2191,9 +2191,9 @@ This function looks for connection-local variables according to
 @var{criteria}, and immediately applies them in the current buffer.
 @end defun
 
-@defmac with-connection-local-profiles profiles &rest body
-All connection-local variables, which are specified by a connection
-profile in @var{profiles}, are applied.
+@defmac with-connection-local-variables &rest body
+All connection-local variables, which are specified by
+@code{default-directory}, are applied.
 
 After that, @var{body} is executed, and the connection-local variables
 are unwound.  Example:
@@ -2207,8 +2207,15 @@ are unwound.  Example:
 @end group
 
 @group
-(with-connection-local-profiles '(remote-perl)
-  do something useful)
+(connection-local-set-profiles
+  '(:application 'tramp :protocol "ssh" :machine "remotehost")
+  'remote-perl)
+@end group
+
+@group
+(let ((default-directory "/ssh:remotehost:/working/dir/"))
+  (with-connection-local-variables
+    do something useful))
 @end group
 @end example
 @end defmac
diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index db3b3f7fee5..ea6ad15dc3d 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -2970,7 +2970,7 @@ Starting with Emacs 26, you could use connection-local variables for
 setting different values of @code{explicit-shell-file-name} for
 different remote hosts.
 @ifinfo
-@pxref{Connection Local Variables, , , elisp}
+@xref{Connection Variables, , , emacs}
 @end ifinfo
 
 @lisp
@@ -3023,6 +3023,14 @@ host.  Example:
 @kbd{M-x auto-revert-tail-mode @key{RET}} runs similarly showing
 continuous output.
 
+@code{shell-command} uses the variables @code{shell-file-name} and
+@code{shell-command-switch} in order to determine which shell to run.
+For remote hosts, their default values are @file{/bin/sh} and
+@option{-c}, respectively (except for the @option{adb} method, which
+uses @file{/system/bin/sh}).  Like the variables in the previous
+section, these variables can be changed via connection-local
+variables.
+
 
 @subsection Running @code{eshell} on a remote host
 @cindex @code{eshell}