Method parameters inspect

Example:

    def m(a, b=nil, *c, d:, e: nil, **rest, &block)
    end
    p method(:m)
    #=> #<Method: m(a, b=<default>, *c, d:, e: <default>, **rest, &block) ...>

1 files changed, 58 insertions, 1 deletions

diff --git a/proc.c b/proc.c
index 2dc625b41e..e37ac1ceb3 100644
--- a/proc.c
+++ b/proc.c
@@ -2827,7 +2827,64 @@ method_inspect(VALUE method)
     }
 
     // parameter information
-    // TODO
+    {
+        VALUE params = rb_method_parameters(method);
+        VALUE pair, name, kind;
+        int arg_num = 1;
+        const VALUE req = ID2SYM(rb_intern("req"));
+        const VALUE opt = ID2SYM(rb_intern("opt"));
+        const VALUE keyreq = ID2SYM(rb_intern("keyreq"));
+        const VALUE key = ID2SYM(rb_intern("key"));
+        const VALUE rest = ID2SYM(rb_intern("rest"));
+        const VALUE keyrest = ID2SYM(rb_intern("keyrest"));
+        const VALUE block = ID2SYM(rb_intern("block"));
+        const VALUE nokey = ID2SYM(rb_intern("nokey"));
+
+        rb_str_buf_cat2(str, "(");
+
+        for (int i = 0; i < RARRAY_LEN(params); i++) {
+            pair = RARRAY_AREF(params, i);
+            kind = RARRAY_AREF(pair, 0);
+            name = RARRAY_AREF(pair, 1);
+            // FIXME: in tests it turns out that kind, name = [:req] produces name to be false. Why?..
+            if (NIL_P(name) || name == Qfalse) {
+                // FIXME: can it be reduced to switch/case?
+                if (kind == req || kind == opt) {
+                    name = rb_sprintf("arg%d", arg_num);
+                    arg_num++;
+                } else if (kind == rest || kind == keyrest) {
+                    name = rb_str_new2("");
+                } else if (kind == block) {
+                    name = rb_str_new2("block");
+                } else if (kind == nokey) {
+                    name = rb_str_new2("nil");
+                }
+            }
+
+            if (kind == req) {
+                rb_str_catf(str, "%"PRIsVALUE, name);
+            } else if (kind == opt) {
+                rb_str_catf(str, "%"PRIsVALUE"=<default>", name);
+            } else if (kind == keyreq) {
+                rb_str_catf(str, "%"PRIsVALUE":", name);
+            } else if (kind == key) {
+                rb_str_catf(str, "%"PRIsVALUE": <default>", name);
+            } else if (kind == rest) {
+                rb_str_catf(str, "*%"PRIsVALUE, name);
+            } else if (kind == keyrest) {
+                rb_str_catf(str, "**%"PRIsVALUE, name);
+            } else if (kind == block) {
+                rb_str_catf(str, "&%"PRIsVALUE, name);
+            } else if (kind == nokey) {
+                rb_str_buf_cat2(str, "**nil");
+            }
+
+            if (i < RARRAY_LEN(params) - 1) {
+                rb_str_buf_cat2(str, ", ");
+            }
+        }
+        rb_str_buf_cat2(str, ")");
+    }
 
     { // source location
         VALUE loc = rb_method_location(method);