loader: add `last_loader_error` to handle the potential error messages.

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/src/loader.nit b/src/loader.nit
index d1e4997..0cd3331 100644 (file)
--- a/src/loader.nit
+++ b/src/loader.nit
@@ -154,7 +154,10 @@ redef class ModelBuilder
 
                        var mmodule = identify_module(a)
                        if mmodule == null then
-                               if a.file_exists then
+                               var le = last_loader_error
+                               if le != null then
+                                       toolcontext.error(null, le)
+                               else if a.file_exists then
                                        toolcontext.error(null, "Error: `{a}` is not a Nit source file.")
                                else
                                        toolcontext.error(null, "Error: cannot find module `{a}`.")
@@ -324,6 +327,14 @@ redef class ModelBuilder
        # A parsed module exists in the model but might be not yet analysed (no importation).
        var parsed_modules = new Array[MModule]
 
+       # Some `loader` services are silent and return `null` on error.
+       #
+       # Those services can set `last_loader_error` to precise an specific error message.
+       # if `last_loader_error == null` then a generic error message can be used.
+       #
+       # See `identified_modules` and `identify_group` for details.
+       var last_loader_error: nullable String = null
+
        # Identify a source file and load the associated package and groups if required.
        #
        # This method does what the user expects when giving an argument to a Nit tool.
@@ -336,11 +347,14 @@ redef class ModelBuilder
        #   then the main module of the package `digraph` is searched in `paths` and returned.
        #
        # Silently return `null` if `path` does not exists or cannot be identified.
+       # If `null` is returned, `last_loader_error` can be set to a specific error message.
        #
        # On success, it returns a module that is possibly not yet parsed (no AST), or not yet analysed (no importation).
        # If the module was already identified, or loaded, it is returned.
        fun identify_module(path: String): nullable MModule
        do
+               last_loader_error = null
+
                # special case for not a nit file
                if not path.has_suffix(".nit") then
                        # search dirless files in known -I paths
@@ -419,9 +433,16 @@ redef class ModelBuilder
        # Return the mgroup associated to a directory path.
        # If the directory is not a group null is returned.
        #
+       # Silently return `null` if `dirpath` does not exists, is not a directory,
+       # cannot be identified or cannot be attached to a mpackage.
+       # If `null` is returned, `last_loader_error` can be set to a specific error message.
+       #
        # Note: `paths` is also used to look for mgroups
        fun identify_group(dirpath: String): nullable MGroup
        do
+               # Reset error
+               last_loader_error = null
+
                var stat = dirpath.file_stat
 
                if stat == null or not stat.is_dir then do
@@ -440,6 +461,7 @@ redef class ModelBuilder
 
                # Filter out non-directories
                if not stat.is_dir then
+                       last_loader_error = "Error: `{dirpath}` is not a directory."
                        return null
                end
 
@@ -466,6 +488,7 @@ redef class ModelBuilder
                        # The root of the directory hierarchy in the file system.
                        if rdp == "/" then
                                mgroups[rdp] = null
+                               last_loader_error = "Error: `{dirpath}` is not a Nit package."
                                return null
                        end
 
@@ -473,6 +496,7 @@ redef class ModelBuilder
                        if (dirpath/"packages.ini").file_exists then
                                # dirpath cannot be a package since it is a package directory
                                mgroups[rdp] = null
+                               last_loader_error = "Error: `{dirpath}` is not a Nit package."
                                return null
                        end
 
@@ -492,6 +516,7 @@ redef class ModelBuilder
                                if parent == null then
                                        # Parent is not a group, thus we are not a group either
                                        mgroups[rdp] = null
+                                       last_loader_error = "Error: `{dirpath}` is not a Nit package."
                                        return null
                                end
                        end
@@ -653,7 +678,10 @@ redef class ModelBuilder
                # Look for the module
                var mmodule = identify_module(filename)
                if mmodule == null then
-                       if filename.file_exists then
+                       var le = last_loader_error
+                       if le != null then
+                               toolcontext.error(null, le)
+                       else if filename.file_exists then
                                toolcontext.error(null, "Error: `{filename}` is not a Nit source file.")
                        else
                                toolcontext.error(null, "Error: cannot find module `{filename}`.")