commit cfa10dfeac01ae25a7acd6857fae0b377b625779
Author: Jimmy Aguilar Mena <kratsbinovish@gmail.com>
Date:   Tue Mar 19 17:57:25 2024 +0100

    Add basic project-build-dir implementation
    
    This is just a dummy prototype to discuss about alternatives.

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index ac18aceadcf..0ca4ca85566 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -51,6 +51,9 @@
 ;; files inside the root must not be considered a part of it).  It
 ;; should be consistent with `project-files'.
 ;;
+;; `project-build-dir' can be overridden if the project backend has some
+;; extra information about the project build directory.
+;;
 ;; This list can change in future versions.
 ;;
 ;; Transient project:
@@ -208,6 +211,12 @@ project-prompter
   :group 'project
   :version "30.1")
 
+(defcustom project-build-dir nil
+  "Build directory for current project."
+  :type 'directory
+  :safe t
+  :version "30.1")
+
 ;;;###autoload
 (defun project-current (&optional maybe-prompt directory)
   "Return the project instance in DIRECTORY, defaulting to `default-directory'.
@@ -289,8 +298,30 @@ project-external-roots
 headers search path, load path, class path, and so on."
   nil)
 
+(cl-defgeneric project-build-dir (_project)
+  "Return build directory of the current PROJECT.
+
+This function is intended to be defined by the backend when possible.
+Otherwise this returns nil and the `project-compile' command will be
+called in the project-root.
+If the user defines the directory-local variable `project-build-dir' it
+will have precedence over the result of this function."
+ nil)
+
+(defun project-get-build-dir (project)
+  "Return build directory of the current PROJECT.
+If the variable `project-build-dir' is defined, this function returns
+it, otherwise it returns the project root.  If the defined path is
+relative, this expands it relatively to the project's root"
+  (let ((dir (or project-build-dir
+                 (project-build-dir project)
+                 (project-root project)))) ;; I assume project-root is absolute
+    (if (file-name-absolute-p dir)
+        dir
+      (expand-file-name dir (project-root project)))))
+
 (cl-defgeneric project-name (project)
-  "A human-readable name for the project.
+  "A human-readable name for the PROJECT.
 Nominally unique, but not enforced."
   (file-name-nondirectory (directory-file-name (project-root project))))
 
@@ -1391,7 +1422,7 @@ project-compile
   "Run `compile' in the project root."
   (declare (interactive-only compile))
   (interactive)
-  (let ((default-directory (project-root (project-current t)))
+  (let ((default-directory (project-get-build-dir (project-current t)))
         (compilation-buffer-name-function
          (or project-compilation-buffer-name-function
              compilation-buffer-name-function)))