Allow setting the values of variable aliases in Eshell

This makes commands like "COLUMNS=40 some-command" work as expected.

* lisp/eshell/esh-cmd.el (eshell-subcommand-bindings): Remove
'process-environment' from here...

* lisp/eshell/esh-var.el (eshell-var-initialize): ... and add to here,
along with 'eshell-variable-aliases-list'.
(eshell-inside-emacs): Convert to a 'defvar-local' to make it settable
in a particular Eshell buffer.
(eshell-variable-aliases-list): Make $?, $$, and $* read-only and
update docstring.
(eshell-set-variable): New function...
(eshell-handle-local-variables, eshell/export, eshell/unset): ... use
it.
(eshell/set, pcomplete/eshell-mode/set): New functions.
(eshell-get-variable): Get the variable alias's getter function when
appropriate and use a safer method for checking function arity.

* test/lisp/eshell/esh-var-tests.el (esh-var-test/set/env-var)
(esh-var-test/set/symbol, esh-var-test/unset/env-var)
(esh-var-test/unset/symbol, esh-var-test/setq, esh-var-test/export)
(esh-var-test/local-variables, esh-var-test/alias/function)
(esh-var-test/alias/function-pair, esh-var-test/alias/string)
(esh-var-test/alias/string/prefer-lisp, esh-var-test/alias/symbol)
(esh-var-test/alias/symbol-pair, esh-var-test/alias/export)
(esh-var-test/alias/local-variables): New tests.

* doc/misc/eshell.texi (Built-ins): Add 'set' and update 'unset'
documentation.
(Variables): Expand documentation of how to get/set variables.

1 files changed, 145 insertions, 0 deletions

diff --git a/test/lisp/eshell/esh-var-tests.el b/test/lisp/eshell/esh-var-tests.el
index ad695e45d7e..a7ac52ed24a 100644
--- a/test/lisp/eshell/esh-var-tests.el
+++ b/test/lisp/eshell/esh-var-tests.el
@@ -25,6 +25,7 @@
 
 (require 'ert)
 (require 'esh-mode)
+(require 'esh-var)
 (require 'eshell)
 
 (require 'eshell-tests-helpers
@@ -440,6 +441,150 @@ inside double-quotes"
                                "000"))
 
 
+;; Variable-related commands
+
+(ert-deftest esh-var-test/set/env-var ()
+  "Test that `set' with a string variable name sets an environment variable."
+  (with-temp-eshell
+   (eshell-match-command-output "set VAR hello" "hello\n")
+   (should (equal (getenv "VAR") "hello")))
+  (should-not (equal (getenv "VAR") "hello")))
+
+(ert-deftest esh-var-test/set/symbol ()
+  "Test that `set' with a symbol variable name sets a Lisp variable."
+  (let (eshell-test-value)
+    (eshell-command-result-equal "set #'eshell-test-value hello"
+                                 "hello")
+    (should (equal eshell-test-value "hello"))))
+
+(ert-deftest esh-var-test/unset/env-var ()
+  "Test that `unset' with a string variable name unsets an env var."
+  (let ((process-environment (cons "VAR=value" process-environment)))
+    (with-temp-eshell
+     (eshell-match-command-output "unset VAR" "\\`\\'")
+     (should (equal (getenv "VAR") nil)))
+    (should (equal (getenv "VAR") "value"))))
+
+(ert-deftest esh-var-test/unset/symbol ()
+  "Test that `unset' with a symbol variable name unsets a Lisp variable."
+  (let ((eshell-test-value "value"))
+    (eshell-command-result-equal "unset #'eshell-test-value" nil)
+    (should (equal eshell-test-value nil))))
+
+(ert-deftest esh-var-test/setq ()
+  "Test that `setq' sets Lisp variables."
+  (let (eshell-test-value)
+    (eshell-command-result-equal "setq eshell-test-value hello"
+                                 "hello")
+    (should (equal eshell-test-value "hello"))))
+
+(ert-deftest esh-var-test/export ()
+  "Test that `export' sets environment variables."
+  (with-temp-eshell
+   (eshell-match-command-output "export VAR=hello" "\\`\\'")
+   (should (equal (getenv "VAR") "hello"))))
+
+(ert-deftest esh-var-test/local-variables ()
+  "Test that \"VAR=value command\" temporarily sets variables."
+  (with-temp-eshell
+   (push "VAR=value" process-environment)
+   (eshell-match-command-output "VAR=hello env" "VAR=hello\n")
+   (should (equal (getenv "VAR") "value"))))
+
+
+;; Variable aliases
+
+(ert-deftest esh-var-test/alias/function ()
+  "Test using a variable alias defined as a function."
+  (with-temp-eshell
+   (push `("ALIAS" ,(lambda () "value") nil t) eshell-variable-aliases-list)
+   (eshell-match-command-output "echo $ALIAS" "value\n")
+   (eshell-match-command-output "set ALIAS hello"
+                                "Variable `ALIAS' is not settable\n"
+                                nil t)))
+
+(ert-deftest esh-var-test/alias/function-pair ()
+  "Test using a variable alias defined as a pair of getter/setter functions."
+  (with-temp-eshell
+   (let ((eshell-test-value "value"))
+     (push `("ALIAS" (,(lambda () eshell-test-value)
+                      . (lambda (_ value)
+                          (setq eshell-test-value (upcase value))))
+             nil t)
+           eshell-variable-aliases-list)
+     (eshell-match-command-output "echo $ALIAS" "value\n")
+     (eshell-match-command-output "set ALIAS hello" "HELLO\n")
+     (should (equal eshell-test-value "HELLO")))))
+
+(ert-deftest esh-var-test/alias/string ()
+  "Test using a variable alias defined as a string.
+This should get/set the aliased environment variable."
+  (with-temp-eshell
+   (let ((eshell-test-value "lisp-value"))
+     (push "eshell-test-value=env-value" process-environment)
+     (push `("ALIAS" "eshell-test-value") eshell-variable-aliases-list)
+     (eshell-match-command-output "echo $ALIAS" "env-value\n")
+     (eshell-match-command-output "set ALIAS hello" "hello\n")
+     (should (equal (getenv "eshell-test-value") "hello"))
+     (should (equal eshell-test-value "lisp-value")))))
+
+(ert-deftest esh-var-test/alias/string/prefer-lisp ()
+  "Test using a variable alias defined as a string.
+This sets `eshell-prefer-lisp-variables' to t and should get/set
+the aliased Lisp variable."
+  (with-temp-eshell
+   (let ((eshell-test-value "lisp-value")
+         (eshell-prefer-lisp-variables t))
+     (push "eshell-test-value=env-value" process-environment)
+     (push `("ALIAS" "eshell-test-value") eshell-variable-aliases-list)
+     (eshell-match-command-output "echo $ALIAS" "lisp-value\n")
+     (eshell-match-command-output "set ALIAS hello" "hello\n")
+     (should (equal (car process-environment) "eshell-test-value=env-value"))
+     (should (equal eshell-test-value "hello")))))
+
+(ert-deftest esh-var-test/alias/symbol ()
+  "Test using a variable alias defined as a symbol.
+This should get/set the value bound to the symbol."
+  (with-temp-eshell
+   (let ((eshell-test-value "value"))
+     (push '("ALIAS" eshell-test-value) eshell-variable-aliases-list)
+     (eshell-match-command-output "echo $ALIAS" "value\n")
+     (eshell-match-command-output "set ALIAS hello" "hello\n")
+     (should (equal eshell-test-value "hello")))))
+
+(ert-deftest esh-var-test/alias/symbol-pair ()
+  "Test using a variable alias defined as a pair of symbols.
+This should get the value bound to the symbol, but fail to set
+it, since the setter is nil."
+  (with-temp-eshell
+   (let ((eshell-test-value "value"))
+     (push '("ALIAS" (eshell-test-value . nil)) eshell-variable-aliases-list)
+     (eshell-match-command-output "echo $ALIAS" "value\n")
+     (eshell-match-command-output "set ALIAS hello"
+                                "Variable `ALIAS' is not settable\n"
+                                nil t))))
+
+(ert-deftest esh-var-test/alias/export ()
+  "Test that `export' properly sets variable aliases."
+  (with-temp-eshell
+   (let ((eshell-test-value "value"))
+     (push `("ALIAS" (,(lambda () eshell-test-value)
+                      . (lambda (_ value) (setq eshell-test-value value)))
+             nil t)
+           eshell-variable-aliases-list)
+     (eshell-match-command-output "export ALIAS=hello" "\\`\\'")
+     (should (equal eshell-test-value "hello")))))
+
+(ert-deftest esh-var-test/alias/local-variables ()
+  "Test that \"VAR=value cmd\" temporarily sets read-only variable aliases."
+  (with-temp-eshell
+   (let ((eshell-test-value "value"))
+     (push `("ALIAS" ,(lambda () eshell-test-value) t t)
+           eshell-variable-aliases-list)
+     (eshell-match-command-output "ALIAS=hello env" "ALIAS=hello\n")
+     (should (equal eshell-test-value "value")))))
+
+
 ;; Built-in variables
 
 (ert-deftest esh-var-test/lines-var ()