toolbox.sh: Allow modules to implement their own interface

The interface/implements mechanism does not allow a module to
implement methods of the interface that it declares. This makes it
impossible to write modules that extend other modules.

This commit changes the interface mechanism so that a module may
provide methods of the interface that it declares. This is done by
renaming module functions if they clash with names of the interface's
method stubs.

diff --git a/toolbox.sh b/toolbox.sh
index 71e5725fa6c9f27824b94fba6209fa3a56786e22..c3dd29a378d4773214f47c63110e970fe5120aa3 100644 (file)
--- a/toolbox.sh
+++ b/toolbox.sh
@@ -182,6 +182,40 @@ method_not_implemented() {
        return 127
 }
 
+have_method() {
+       local name="$1"
+
+       if ! declare -f "$name" &> /dev/null; then
+               return 1
+       fi
+
+       return 0
+}
+
+rename_method() {
+       local old_name="$1"
+       local new_name="$2"
+
+       local old_definition
+       local new_definition
+
+       if ! old_definition=$(declare -f "$old_name"); then
+               return 1
+       fi
+
+       new_definition="$new_name${old_definition#* }"
+
+       if ! unset -f "$old_name"; then
+               return 1
+       fi
+
+       if ! source <(echo "$new_definition");  then
+               return 1
+       fi
+
+       return 0
+}
+
 interface() {
        local methods=("$@")
 
@@ -211,6 +245,21 @@ interface() {
                # shellcheck disable=SC2016 # Reason: Don't want expansion in the format string
                call_stubs+=$(printf '\n%s() {\n\t"${%s["%s"]}" "$@"\n\treturn "$?"\n}' \
                                     "${name}_$method" "$vtable_name" "$method")
+               interface["$method"]=method_not_implemented
+       done
+
+       # Rename existing functions if they clash with the call stubs
+       for method in "${methods[@]}"; do
+               if ! have_method "${name}_$method"; then
+                       continue
+               fi
+
+               if ! rename_method "${name}_$method" "___${name}_$method"; then
+                       echo "ERROR: Could not rename function ${name}_$method. Is it readonly?" 1>&2
+                       return 1
+               fi
+
+               interface["$method"]="___${name}_$method"
        done
 
        # shellcheck disable=SC1090 # Reason: Dynamically generated call-stubs can't be checked
@@ -219,11 +268,6 @@ interface() {
                return 1
        fi
 
-       # Set the entries in the vtable
-       for method in "${methods[@]}"; do
-               interface["$method"]=method_not_implemented
-       done
-
        return 0
 }