From 0b3f785c4a272b909108108cf7931779ae48cfba Mon Sep 17 00:00:00 2001
From: Yuan Fu <casouri@gmail.com>
Date: Wed, 12 Oct 2022 10:38:35 -0700
Subject: [PATCH] Better signal data for treesit-load-language-error

* src/treesit.c (ts_load_language): Better formatted signal data,
(Ftreesit_langauge_available_p): Optionally return the signal data if
language not available.
* doc/lispref/parsing.texi: Document the signal data in detail.
---
 doc/lispref/parsing.texi | 26 ++++++++++++++++++--------
 src/treesit.c            | 39 +++++++++++++++++++++++++++------------
 2 files changed, 45 insertions(+), 20 deletions(-)

diff --git a/doc/lispref/parsing.texi b/doc/lispref/parsing.texi
index d0bb642a3e0..c73175e3c37 100644
--- a/doc/lispref/parsing.texi
+++ b/doc/lispref/parsing.texi
@@ -70,16 +70,26 @@ Tree-sitter language definitions are distributed as dynamic libraries.
 In order to use a language definition in Emacs, you need to make sure
 that the dynamic library is installed on the system.  Emacs looks for
 language definitions under load paths in
-@code{treesit-extra-load-path}, @code{user-emacs-directory}/tree-sitter,
-and system default locations for dynamic libraries, in that order.
-Emacs tries each extensions in @code{treesit-load-suffixes}.  If Emacs
-cannot find the library or has problem loading it, Emacs signals
-@code{treesit-load-language-error}.  The signal data is a list of
-specific error messages.
+@code{treesit-extra-load-path},
+@code{user-emacs-directory}/tree-sitter, and system default locations
+for dynamic libraries, in that order.  Emacs tries each extensions in
+@code{treesit-load-suffixes}.  If Emacs cannot find the library or has
+problem loading it, Emacs signals @code{treesit-load-language-error}.
+
+The signal data could be @code{(not-found @var{error-msg} ...)} if
+Emacs cannot find the language definition, or @code{(symbol-error
+@var{error-msg})} if the Emacs cannot find the correct symbol in the
+language definition, or @code{(version_mismatch @var{error-msg})} if
+the language definition's version does match that of the tree-sitter
+library.
 
 @defun treesit-language-available-p language
-This function checks whether the dynamic library for @var{language} is
-present on the system, and return non-nil if it is.
+This function returns non-nil if @var{language} exists and is
+loadable.
+
+If @var{detail} is non-nil, return @code{(t . nil) when @var{language}
+is available, @code{(nil . DATA)} when unavailable.  @var{data} is the
+signal data of @code{treesit-load-language-error}.
 @end defun
 
 @vindex treesit-load-name-override-list
diff --git a/src/treesit.c b/src/treesit.c
index 2565464deac..2b2e9c6d793 100644
--- a/src/treesit.c
+++ b/src/treesit.c
@@ -193,10 +193,7 @@ ts_load_language_push_for_each_suffix
 }
 
 /* Load the dynamic library of LANGUAGE_SYMBOL and return the pointer
-   to the language definition.  Signals
-   Qtreesit_load_language_error if something goes wrong.
-   Qtreesit_load_language_error carries the error message from
-   trying to load the library with each extension.
+   to the language definition.
 
    If error occurs, return NULL and fill SIGNAL_SYMBOL and SIGNAL_DATA
    with values suitable for xsignal. */
@@ -267,7 +264,7 @@ ts_load_language (Lisp_Object language_symbol,
   if (error != NULL)
     {
       *signal_symbol = Qtreesit_load_language_error;
-      *signal_data = list2 (symbol_name, Fnreverse (error_list));
+      *signal_data = Fcons (Qnot_found, Fnreverse (error_list));
       return NULL;
     }
 
@@ -279,7 +276,7 @@ ts_load_language (Lisp_Object language_symbol,
   if (error != NULL)
     {
       *signal_symbol = Qtreesit_load_language_error;
-      *signal_data = build_string (error);
+      *signal_data = list2 (Qsymbol_error, build_string (error));
       return NULL;
     }
   TSLanguage *lang = (*langfn) ();
@@ -291,7 +288,7 @@ ts_load_language (Lisp_Object language_symbol,
   if (!success)
     {
       *signal_symbol = Qtreesit_load_language_error;
-      *signal_data = list2 (build_pure_c_string ("Language version doesn't match tree-sitter version, language version:"),
+      *signal_data = list2 (Qversion_mismatch,
 			    make_fixnum (ts_language_version (lang)));
       return NULL;
     }
@@ -301,18 +298,32 @@ ts_load_language (Lisp_Object language_symbol,
 DEFUN ("treesit-language-available-p",
        Ftreesit_langauge_available_p,
        Streesit_language_available_p,
-       1, 1, 0,
-       doc: /* Return non-nil if LANGUAGE exists and is loadable.  */)
-  (Lisp_Object language)
+       1, 2, 0,
+       doc: /* Return non-nil if LANGUAGE exists and is loadable.
+
+If DETAIL is non-nil, return (t . nil) when LANGUAGE is available,
+(nil . DATA) when unavailable.  DATA is the signal data of
+`treesit-load-language-error'.  */)
+  (Lisp_Object language, Lisp_Object detail)
 {
   CHECK_SYMBOL (language);
   ts_initialize ();
   Lisp_Object signal_symbol = Qnil;
   Lisp_Object signal_data = Qnil;
   if (ts_load_language(language, &signal_symbol, &signal_data) == NULL)
-    return Qnil;
+    {
+      if (NILP (detail))
+	return Qnil;
+      else
+	return Fcons (Qnil, signal_data);
+    }
   else
-    return Qt;
+    {
+      if (NILP (detail))
+	return Qt;
+      else
+	return Fcons (Qt, Qnil);
+    }
 }
 
 DEFUN ("treesit-language-version",
@@ -2299,6 +2310,10 @@ syms_of_treesit (void)
   DEFSYM (Qhas_changes, "has-changes");
   DEFSYM (Qhas_error, "has-error");
 
+  DEFSYM (Qnot_found, "not-found");
+  DEFSYM (Qsymbol_error, "symbol-error");
+  DEFSYM (Qversion_mismatch, "version-mismatch");
+
   DEFSYM (Qtreesit_error, "treesit-error");
   DEFSYM (Qtreesit_query_error, "treesit-query-error");
   DEFSYM (Qtreesit_parse_error, "treesit-parse-error");
-- 
2.39.2