bug#61051: treesit-install-language-grammar can provide the default repository URL

[Dmitry Gutov <dgutov@yandex.ru>]

On 25/01/2023 14:29, Eli Zaretskii wrote:
>> Date: Wed, 25 Jan 2023 05:23:37 +0200
>> From: Dmitry Gutov<dgutov@yandex.ru>
>>
>> The formathttps://github.com/tree-sitter/tree-sitter-%s  will work for a
>> lot of languages, and the user won't even have to search for the address.
>>
>> The patch can look like this:
>>
>> diff --git a/lisp/treesit.el b/lisp/treesit.el
>> index 660039cc7cc..c1b98d085e8 100644
>> --- a/lisp/treesit.el
>> +++ b/lisp/treesit.el
>> @@ -2708,7 +2708,8 @@ treesit--install-language-grammar-build-recipe
>>          (list
>>           lang
>>           (read-string
>> -        "Enter the URL of the Git repository of the language grammar: ")
>> +        "Enter the URL of the Git repository of the language grammar: "
>> +        (format"https://github.com/tree-sitter/tree-sitter-%s"  lang))
>>           (empty-string-to-nil
>>            (read-string
>>             "Enter the tag or branch (default: default branch): "))
> Sounds good, but wouldn't we confuse users in those cases where the
> Tree-sitter site doesn't have a grammar?  Would it be perhaps feasible
> to probe first that a Git repository at the URL exists?

Sure, how about this:

diff --git a/lisp/treesit.el b/lisp/treesit.el
index 660039cc7cc..4c9bdfc0bd4 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -2707,8 +2707,10 @@ treesit--install-language-grammar-build-recipe
                    (if (equal string "") nil string)))
        (list
         lang
-       (read-string
-        "Enter the URL of the Git repository of the language grammar: ")
+       (let ((repo-default (format 
"https://github.com/tree-sitter/tree-sitter-%s" lang)))
+         (read-string
+          "Enter the URL of the Git repository of the language grammar: "
+          (and (treesit--check-repo-url repo-default) repo-default)))
         (empty-string-to-nil
          (read-string
           "Enter the tag or branch (default: default branch): "))
@@ -2722,6 +2724,16 @@ treesit--install-language-grammar-build-recipe
          (read-string
           "Enter the C++ compiler to use (default: auto-detect): "))))))

+(defun treesit--check-repo-url (url)
+  (defvar url-request-method)
+  (let ((url-request-method "HEAD"))
+    (let ((buffer (condition-case nil (url-retrieve-synchronously url t t)
+                    (file-error nil))))
+      (and buffer
+           (eql
+            (buffer-local-value 'url-http-response-status buffer)
+            200)))))
+
  ;;;###autoload
  (defun treesit-install-language-grammar (lang)
    "Build and install the tree-sitter language grammar library for LANG.