Change yas-lookup-snippet to return a yas--template struct

This allows proper handling of a snippet's expand-env field when doing

    (yas-expand-snippet (yas-lookup-snippet NAME))

* yasnippet.el (yas-expand-snippet): Return the yas--template struct
instead of snippet body.
(yas-expand-snippet): Let first argument be a yas--template struct.
* yasnippet-tests.el (snippet-lookup, snippet-load-uuid): Update tests
accordingly.
(yas-lookup-snippet-with-env): New test.

yasnippet-tests.el

@@ -1031,11 +1031,28 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
   "Test `yas-lookup-snippet'."
   (yas-with-some-interesting-snippet-dirs
    (yas-reload-all 'no-jit)
-   (should (equal (yas-lookup-snippet "printf" 'c-mode) "printf($1);"))
+   (should (equal (yas--template-content (yas-lookup-snippet "printf" 'c-mode))
-   (should (equal (yas-lookup-snippet "def" 'c-mode) "# define"))
+                  "printf($1);"))
+   (should (equal (yas--template-content (yas-lookup-snippet "def" 'c-mode))
+                  "# define"))
    (should-not (yas-lookup-snippet "no such snippet" nil 'noerror))
    (should-not (yas-lookup-snippet "printf" 'emacs-lisp-mode 'noerror))))
 
+(ert-deftest yas-lookup-snippet-with-env ()
+  (with-temp-buffer
+    (yas-with-snippet-dirs
+      '((".emacs.d/snippets"
+         ("emacs-lisp-mode"
+          ("foo" . "\
+# expand-env: ((foo \"bar\"))
+# --
+`foo`"))))
+      (yas-reload-all)
+      (emacs-lisp-mode)
+      (yas-minor-mode +1)
+      (yas-expand-snippet (yas-lookup-snippet "foo"))
+      (should (equal (buffer-string) "bar")))))
+
 (ert-deftest basic-jit-loading ()
   "Test basic loading and expansion of snippets"
   (yas-with-some-interesting-snippet-dirs
@@ -1063,13 +1080,15 @@ hello ${1:$(when (stringp yas-text) (funcall func yas-text))} foo${1:$$(concat \
    (with-temp-buffer
      (text-mode)
      (yas-minor-mode +1)
-     (should (equal (yas-lookup-snippet "one") "one"))
+     (should (equal (yas--template-content (yas-lookup-snippet "one"))
+                    "one"))
      (should (eq (yas--key-binding "\C-c1") 'yas-expand-from-keymap))
      (yas-define-snippets
       'text-mode '(("_1" "one!" "won" nil nil nil nil nil "uuid-1")))
      (should (null (yas-lookup-snippet "one" nil 'noerror)))
      (should (null (yas--key-binding "\C-c1")))
-     (should (equal (yas-lookup-snippet "won") "one!")))))
+     (should (equal (yas--template-content(yas-lookup-snippet "won"))
+                    "one!")))))
 
 (ert-deftest snippet-save ()
   "Make sure snippets can be saved correctly."

yasnippet.el

@@ -2412,18 +2412,17 @@ Honours `yas-choose-tables-first', `yas-choose-keys-first' and
              :key #'yas--template-name :test #'string=)))
 
 (defun yas-lookup-snippet (name &optional mode noerror)
-  "Get the snippet content for the snippet NAME in MODE's tables.
+  "Get the snippet named NAME in MODE's tables.
 
 MODE defaults to the current buffer's `major-mode'.  If NOERROR
 is non-nil, then don't signal an error if there isn't any snippet
 called NAME.
 
 Honours `yas-buffer-local-condition'."
-  (let ((snippet (yas--lookup-snippet-1 name mode)))
   (cond
-     (snippet (yas--template-content snippet))
+   ((yas--lookup-snippet-1 name mode))
    (noerror nil)
-     (t (error "No snippet named: %s" name)))))
+   (t (error "No snippet named: %s" name))))
 
 (defun yas-insert-snippet (&optional no-condition)
   "Choose a snippet to expand, pop-up a list of choices according
@@ -3783,12 +3782,17 @@ Move the overlays, or create them if they do not exit."
 ;; running, but if managed correctly (including overlay priorities)
 ;; they should account for all situations...
 
-(defun yas-expand-snippet (content &optional start end expand-env)
+(defun yas-expand-snippet (snippet &optional start end expand-env)
-  "Expand snippet CONTENT at current point.
+  "Expand SNIPPET at current point.
 
 Text between START and END will be deleted before inserting
-template.  EXPAND-ENV is a list of (SYM VALUE) let-style dynamic bindings
+template.  EXPAND-ENV is a list of (SYM VALUE) let-style dynamic
-considered when expanding the snippet."
+bindings considered when expanding the snippet.  If omitted, use
+SNIPPET's expand-env field.
+
+SNIPPET may be a snippet structure (e.g., as returned by
+`yas-lookup-snippet'), or just a string representing a snippet's
+body text."
   (cl-assert (and yas-minor-mode
                   (memq 'yas--post-command-handler post-command-hook))
              nil
@@ -3820,17 +3824,19 @@ considered when expanding the snippet."
           (cond (yas-selected-text)
                 ((and (region-active-p)
                       (not clear-field))
-                 to-delete)))
+                 to-delete))))
-         snippet)
     (goto-char start)
     (setq yas--indent-original-column (current-column))
     ;; Delete the region to delete, this *does* get undo-recorded.
     (when to-delete
       (delete-region start end))
 
+    (let ((content (if (stringp snippet) snippet
+                     (yas--template-content snippet))))
+      (when (and (not expand-env) (yas--template-p snippet))
+        (setq expand-env (yas--template-expand-env snippet)))
       (cond ((listp content)
-           ;; x) This is a snippet-command
+             ;; x) This is a snippet-command.
-           ;;
              (yas--eval-for-effect content))
             (t
              ;; x) This is a snippet-snippet :-)
@@ -3840,9 +3846,8 @@ considered when expanding the snippet."
                (setq snippet
                      (yas--snippet-create content expand-env start (point))))
 
-           ;; stacked-expansion: This checks for stacked expansion, save the
+             ;; Stacked-expansion: This checks for stacked expansion, save the
              ;; `yas--previous-active-field' and advance its boundary.
-           ;;
              (let ((existing-field (and yas--active-field-overlay
                                         (overlay-buffer yas--active-field-overlay)
                                         (overlay-get yas--active-field-overlay 'yas--field))))
@@ -3850,13 +3855,11 @@ considered when expanding the snippet."
                  (setf (yas--snippet-previous-active-field snippet) existing-field)
                  (yas--advance-end-maybe existing-field (overlay-end yas--active-field-overlay))))
 
-           ;; Exit the snippet immediately if no fields
+             ;; Exit the snippet immediately if no fields.
-           ;;
              (unless (yas--snippet-fields snippet)
                (yas-exit-snippet snippet))
 
-           ;; Now, schedule a move to the first field
+             ;; Now, schedule a move to the first field.
-           ;;
              (let ((first-field (car (yas--snippet-fields snippet))))
                (when first-field
                  (sit-for 0) ;; fix issue 125
@@ -3869,7 +3872,7 @@ considered when expanding the snippet."
                    ;; Keep region for ${0:exit text}.
                    (setq deactivate-mark nil))))
              (yas--message 4 "snippet %d expanded." (yas--snippet-id snippet))
-           t))))
+             t)))))
 
 (defun yas--take-care-of-redo (snippet)
   "Commits SNIPPET, which in turn pushes an undo action for reviving it.