>From 3f56b3641ba75430210325bcfd0c1bdff16f2a01 Mon Sep 17 00:00:00 2001
From: Federico Tedin <federicotedin@gmail.com>
Date: Mon, 30 Mar 2020 21:44:47 +0200
Subject: [PATCH] Copy INSIDE_EMACS env variable to subprocesses in Eshell

* lisp/eshell/em-dirs.el (eshell-dirs-initialize): Add INSIDE_EMACS
variable to buffer-local value of eshell-variable-aliases-alist.
(eshell-inside-emacs): Add new constant used for INSIDE_EMACS.
* lisp/eshell/esh-var.el (eshell-variable-aliases-list): Update doc
string; remove mention of eshell-user-aliases-list and explain that
variables can optionally be copied to subprocesses' environments.
* test/lisp/eshell/eshell-tests.el (eshell-test/inside-emacs-var): Add
test for the INSIDE_EMACS variable.
* etc/NEWS: Announce changes.
---
 etc/NEWS                         |  6 ++++++
 lisp/eshell/em-dirs.el           |  5 +++++
 lisp/eshell/esh-var.el           | 23 ++++++++++++++++++-----
 test/lisp/eshell/eshell-tests.el |  7 +++++++
 4 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 4b477e5def..9ac90ecabf 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -161,6 +161,12 @@ functions accessible to the user through the existing single function hook
 Modes should use the new hook instead of this user option to register
 their backends.
 
+** Eshell
+
+---
+*** Environment variable INSIDE_EMACS is now copied to subprocesses.
+Its value equals the result of evaluating '(format "%s,eshell" emacs-version)'.
+
 ** Tramp
 
 +++
diff --git a/lisp/eshell/em-dirs.el b/lisp/eshell/em-dirs.el
index 1949e5dc8f..51df6fa1d5 100644
--- a/lisp/eshell/em-dirs.el
+++ b/lisp/eshell/em-dirs.el
@@ -168,6 +168,9 @@ eshell-dirstack
 (defvar eshell-last-dir-ring nil
   "The last directory that Eshell was in.")
 
+(defconst eshell-inside-emacs (format "%s,eshell" emacs-version)
+  "Value for the `INSIDE_EMACS' environment variable.")
+
 ;;; Functions:
 
 (defun eshell-dirs-initialize ()    ;Called from `eshell-mode' via intern-soft!
@@ -191,6 +194,8 @@ eshell-dirs-initialize
 		        (unless (ring-empty-p eshell-last-dir-ring)
 			  (expand-file-name
 			   (ring-ref eshell-last-dir-ring 0))))
+            t)
+           ("INSIDE_EMACS" eshell-inside-emacs
             t))))
 
   (when eshell-cd-on-directory
diff --git a/lisp/eshell/esh-var.el b/lisp/eshell/esh-var.el
index 327a1def46..c12999ee0d 100644
--- a/lisp/eshell/esh-var.el
+++ b/lisp/eshell/esh-var.el
@@ -179,10 +179,9 @@ eshell-variable-aliases-list
 	      (eshell-apply-indices eshell-command-arguments
 				    indices)))))
   "This list provides aliasing for variable references.
-It is very similar in concept to what `eshell-user-aliases-list' does
-for commands.  Each member of this defines the name of a command,
-and the Lisp value to return for that variable if it is accessed
-via the syntax `$NAME'.
+Each member defines the name of a variable, and a Lisp value used to
+compute the string value that will be returned when the variable is
+accessed via the syntax `$NAME'.
 
 If the value is a function, that function will be called with two
 arguments: the list of the indices that was used in the reference, and
@@ -190,7 +189,21 @@ eshell-variable-aliases-list
 For example, a reference of `$NAME[10][20]' would result in the
 function for alias `NAME' being called (assuming it were aliased to a
 function), and the arguments passed to this function would be the list
-'(10 20)', and nil."
+'(10 20)', and nil.
+
+If the value is a string, the value for the variable with that name in
+the current environment will be returned.  If no variable with that
+name exists in the environment, but if a symbol with that same name
+exists and has a value bound to it, then that value will be used.  You
+can prioritize symbol values over environment values by setting
+`eshell-prefer-lisp-variables' to t.
+
+If the value is a symbol, the value bound to that symbol will be used.
+
+If the value has any other type, `error' will be signaled.
+
+Additionally, each member may specify if it should be copied to the
+environment of created subprocesses."
   :type '(repeat (list string sexp
 		       (choice (const :tag "Copy to environment" t)
 			       (const :tag "Use only in Eshell" nil)))))
diff --git a/test/lisp/eshell/eshell-tests.el b/test/lisp/eshell/eshell-tests.el
index 026818ab06..ce8d728833 100644
--- a/test/lisp/eshell/eshell-tests.el
+++ b/test/lisp/eshell/eshell-tests.el
@@ -169,6 +169,13 @@ eshell-test/last-arg-var
    (eshell-command-result-p "+ 1 2; + $_ 4"
                              "3\n6\n")))
 
+(ert-deftest eshell-test/inside-emacs-var ()
+  "Test presence of \"INSIDE_EMACS\" in subprocesses"
+  (with-temp-eshell
+   (eshell-command-result-p "env"
+                            (format "INSIDE_EMACS=%s,eshell"
+                                    emacs-version))))
+
 (ert-deftest eshell-test/escape-nonspecial ()
   "Test that \"\\c\" and \"c\" are equivalent when \"c\" is not a
 special character."
-- 
2.17.1