Add support for different indent strategies.

Allow different line indentation strategies to be used.  Set the
default strategy to `declaration` so that indentation is recomputed at
the declaration level once valid syntax is available.  This can help
recover from incorrect indentation due to previously syntactically
invalid states of the buffer.

Author: brownts

README.org

@@ -213,11 +213,17 @@ levels to match your own style.
   Continuation indentation for partial expressions (i.e., terms,
   concatenation, etc).
 
-It should be noted that the settings above are defined in terms of
-each other, so that by customizing the standard indentation offset
-~gpr-ts-mode-indent-offset~, the other indentation offsets will be
-adjusted accordingly.  In other words, those settings either use the
-same value or a value derived from it.  Therefore, customizing the
+- User Option: gpr-ts-mode-indent-strategy ::
+  Indentation strategy to use, typically when =RET= or =TAB= are pressed
+  during editing.  Historically, this would drive a line-based
+  indentation, however more complex indentation strategies can be used
+  due to the availability of the syntax tree.
+
+It should be noted that the offsets defined above are described in
+terms of each other, so that by customizing the standard indentation
+offset ~gpr-ts-mode-indent-offset~, the other indentation offsets will
+be adjusted accordingly.  In other words, those settings either use
+the same value or a value derived from it.  Therefore, customizing the
 base value will have an affect on the remaining values as well.  If
 this is not the desired outcome, the other offsets should be
 customized as well.
@@ -227,8 +233,8 @@ indentation will align stacked items under each other.  This applies
 to lists, function call parameters, import lists, discrete choice
 lists in case constructions, etc.
 
-Indentation rules used in gpr-ts-mode (as in all tree-sitter based
-modes) are based on the syntax of the language.  When what currently
+Indentation rules used in ~gpr-ts-mode~, as in all tree-sitter based
+modes, are based on the syntax of the language.  When what currently
 exists in the buffer is not syntactically correct, the in-memory
 syntax tree will contain errors, since the buffer doesn't adhere to
 the grammar rules of the language (i.e., it contains syntax errors).
@@ -248,6 +254,23 @@ declarations, case statements, etc.) are highly recommended.  Not only
 can this help keep your buffer closer to a syntactically correct
 state, you also benefit from the productivity gains as well.
 
+The indentation strategy can help recover from previously incorrect
+indentation that has occurred while the buffer was in a syntactically
+invalid state.  The default ~declaration~ setting for
+=gpr-ts-mode-indent-strategy= will re-indent at the declaration level
+once the declaration is in a syntactically valid state.  When invalid
+syntax exists within a declaration, this strategy reverts back to
+"best effort" line-based indentation.  Once the syntax becomes valid,
+indentation will be applied at the declaration level.
+
+If none of the existing indentation strategies are sufficient, a
+custom strategy can be created and used.  In order to create a
+strategy, a new strategy symbol should be specified in
+=gpr-ts-mode-indent-strategy=, and an implementation of
+=gpr-ts-mode-indent= should be created, specializing on the new strategy
+symbol name.  Refer to existing instances of this function to
+understand how current strategy functions are implemented.
+
 * Navigation
 
 The following specialized navigation functions exist and are applied

doc/gpr-ts-mode.texi

@@ -297,11 +297,18 @@ Continuation indentation for partial expressions (i.e., terms,
 concatenation, etc).
 @end defopt
 
-It should be noted that the settings above are defined in terms of
-each other, so that by customizing the standard indentation offset
-@code{gpr-ts-mode-indent-offset}, the other indentation offsets will be
-adjusted accordingly.  In other words, those settings either use the
-same value or a value derived from it.  Therefore, customizing the
+@defopt gpr-ts-mode-indent-strategy
+Indentation strategy to use, typically when @samp{RET} or @samp{TAB} are pressed
+during editing.  Historically, this would drive a line-based
+indentation, however more complex indentation strategies can be used
+due to the availability of the syntax tree.
+@end defopt
+
+It should be noted that the offsets defined above are described in
+terms of each other, so that by customizing the standard indentation
+offset @code{gpr-ts-mode-indent-offset}, the other indentation offsets will
+be adjusted accordingly.  In other words, those settings either use
+the same value or a value derived from it.  Therefore, customizing the
 base value will have an affect on the remaining values as well.  If
 this is not the desired outcome, the other offsets should be
 customized as well.
@@ -311,8 +318,8 @@ indentation will align stacked items under each other.  This applies
 to lists, function call parameters, import lists, discrete choice
 lists in case constructions, etc.
 
-Indentation rules used in gpr-ts-mode (as in all tree-sitter based
-modes) are based on the syntax of the language.  When what currently
+Indentation rules used in @code{gpr-ts-mode}, as in all tree-sitter based
+modes, are based on the syntax of the language.  When what currently
 exists in the buffer is not syntactically correct, the in-memory
 syntax tree will contain errors, since the buffer doesn't adhere to
 the grammar rules of the language (i.e., it contains syntax errors).
@@ -332,6 +339,23 @@ declarations, case statements, etc.) are highly recommended.  Not only
 can this help keep your buffer closer to a syntactically correct
 state, you also benefit from the productivity gains as well.
 
+The indentation strategy can help recover from previously incorrect
+indentation that has occurred while the buffer was in a syntactically
+invalid state.  The default @code{declaration} setting for
+@samp{gpr-ts-mode-indent-strategy} will re-indent at the declaration level
+once the declaration is in a syntactically valid state.  When invalid
+syntax exists within a declaration, this strategy reverts back to
+``best effort'' line-based indentation.  Once the syntax becomes valid,
+indentation will be applied at the declaration level.
+
+If none of the existing indentation strategies are sufficient, a
+custom strategy can be created and used.  In order to create a
+strategy, a new strategy symbol should be specified in
+@samp{gpr-ts-mode-indent-strategy}, and an implementation of
+@samp{gpr-ts-mode-indent} should be created, specializing on the new strategy
+symbol name.  Refer to existing instances of this function to
+understand how current strategy functions are implemented.
+
 @node Navigation
 @chapter Navigation
 

gpr-ts-mode.el

@@ -125,6 +125,15 @@
   :package-version "0.5.0")
 ;;;###autoload(put 'gpr-ts-mode-indent-exp-item-offset 'safe-local-variable #'integerp)
 
+(defcustom gpr-ts-mode-indent-strategy 'declaration
+  "Indentation strategy to utilize."
+  :type '(choice :tag "Indentation Strategy"
+                 (const :tag "Declaration" declaration)
+                 (const :tag "Line" line))
+  :group 'gpr-ts
+  :link '(custom-manual :tag "Indentation" "(gpr-ts-mode)Indentation")
+  :package-version "0.6.0")
+
 (defcustom gpr-ts-mode-grammar "https://github.com/brownts/tree-sitter-gpr"
   "Configuration for downloading and installing the tree-sitter language grammar.
 
@@ -314,6 +323,50 @@ Return nil if no child of that type is found."
     (lambda (n)
       (equal (treesit-node-type n) type)))))
 
+(cl-defgeneric gpr-ts-mode-indent (strategy)
+  "Indent according to STRATEGY."
+  (error "Unknown indentation strategy: %s" strategy))
+
+(cl-defmethod gpr-ts-mode-indent ((_strategy (eql line)))
+  "Indent according to line STRATEGY."
+  (treesit-indent))
+
+(cl-defmethod gpr-ts-mode-indent ((_strategy (eql declaration)))
+  "Indent according to declaration STRATEGY."
+  (let ((initial-point-column (current-column))
+        (initial-indentation-column (current-indentation))
+        (region
+         (save-excursion
+           (forward-line 0)
+           (skip-chars-forward " \t")
+           (unless (looking-at (rx (* whitespace) eol) t)
+             (let* ((node (treesit-node-at (point)))
+                    (root (treesit-buffer-root-node))
+                    (candidate
+                     (treesit-parent-until
+                      node
+                      (lambda (node)
+                        (or (treesit-node-eq node root)
+                            (string-equal (treesit-node-type node) "ERROR")
+                            (gpr-ts-mode--declaration-p node)))
+                      'include-node)))
+               (when (and (gpr-ts-mode--declaration-p candidate)
+                          (not (treesit-search-subtree candidate "ERROR")))
+                 (cons (treesit-node-start candidate)
+                       (treesit-node-end candidate))))))))
+    (if region
+        (progn
+          (treesit-indent-region (car region) (cdr region))
+          ;; Move point if it was in the indentation.
+          (when (<= initial-point-column
+                    initial-indentation-column)
+            (back-to-indentation)))
+      (treesit-indent))))
+
+(defun gpr-ts-mode--indent-line ()
+  "Indent according to `gpr-ts-mode-indent-strategy'."
+  (gpr-ts-mode-indent gpr-ts-mode-indent-strategy))
+
 (defvar gpr-ts-mode--keywords
   '("abstract" "all" "at"
     "case"
@@ -463,7 +516,7 @@ Return nil if no child of that type is found."
            (gpr-ts-mode--sibling-exists-p "("))
       (gpr-ts-mode--anchor-first-sibling-matching "(")
       0)
-     ;; trival recovery for syntax error or unexpected broken line
+     ;; trivial recovery for syntax error or unexpected broken line
      (catch-all prev-line 0)))
   "Tree-sitter indent rules for `gpr-ts-mode'.")
 
@@ -620,6 +673,16 @@ Return nil if NODE is not an attribute declaration node."
   (when (gpr-ts-mode--attribute-declaration-p node)
     (gpr-ts-mode--tree-text node '("comment") "for" "use")))
 
+(defun gpr-ts-mode--case_construction-p (node)
+  "Determine if NODE is a case construction.
+Return non-nil to indicate it is."
+  (string-equal (treesit-node-type node) "case_construction"))
+
+(defun gpr-ts-mode--empty-declaration-p (node)
+  "Determine if NODE is an empty declaration.
+Return non-nil to indicate it is."
+  (string-equal (treesit-node-type node) "empty_declaration"))
+
 (defun gpr-ts-mode--package-declaration-p (node)
   "Determine if NODE is a package declaration.
 Return non-nil to indicate it is."
@@ -691,12 +754,27 @@ Return non-nil to indicate that it is."
   (and (gpr-ts-mode--variable-declaration-p node)
        (not (gpr-ts-mode--typed-variable-declaration-p node))))
 
+(defun gpr-ts-mode--with-declaration-p (node)
+  "Determine if NODE is a with declaration.
+Return non-nil to indicate that it is."
+  (string-equal (treesit-node-type node) "with_declaration"))
+
+(defun gpr-ts-mode--declaration-p (node)
+  "Determine if NODE is a declaration.
+Return non-nil to indicate that it is."
+  (or (gpr-ts-mode--attribute-declaration-p node)
+      (gpr-ts-mode--case_construction-p node)
+      (gpr-ts-mode--empty-declaration-p node)
+      (gpr-ts-mode--package-declaration-p node)
+      (gpr-ts-mode--project-declaration-p node)
+      (gpr-ts-mode--type-declaration-p node)
+      (gpr-ts-mode--variable-declaration-p node)
+      (gpr-ts-mode--with-declaration-p node)))
+
 (defun gpr-ts-mode--with-clause-name-p (node)
   "Determine if NODE is a string within a with clause."
-  (and (string-equal (treesit-node-type (treesit-node-parent node))
-                     "with_declaration")
-       (string-equal (treesit-node-type node)
-                     "string_literal")))
+  (and (gpr-ts-mode--with-declaration-p (treesit-node-parent node))
+       (string-equal (treesit-node-type node) "string_literal")))
 
 (defun gpr-ts-mode--imenu-index (tree item-p branch-p item-name-fn branch-name-fn)
   "Return Imenu index for a specific item category given TREE.
@@ -939,7 +1017,10 @@ the name of the branch given the branch node."
                 (attribute function number operator package variable)
                 (bracket delimiter error)))
 
-  (treesit-major-mode-setup))
+  (treesit-major-mode-setup)
+
+  ;; Override `treesit-major-mode-setup' settings.
+  (setq-local indent-line-function #'gpr-ts-mode--indent-line))
 
 ;;;###autoload
 (progn

test/gpr-ts-mode-tests.el

@@ -33,6 +33,7 @@
 If EXPECT-ERROR is non-nil, then check for an error in the parse tree,
 otherwise check that there is no error in the parse tree."
   (gpr-ts-mode)
+  (setq-local gpr-ts-mode-indent-strategy 'line)
   (if expect-error
       (should (treesit-search-subtree
                (treesit-buffer-root-node) "ERROR"))