From 890fb2d09d7f9e2d32d310d07c766e7a6db167e4 Mon Sep 17 00:00:00 2001
From: Nick Treleaven <n@trelsoft.com>
Date: Thu, 14 Jan 2021 18:50:06 +0000
Subject: [PATCH] checker: show signature for interface method on error (#8111)

---
 vlib/v/checker/checker.v                           | 3 +++
 vlib/v/checker/tests/unimplemented_interface_b.out | 1 +
 vlib/v/checker/tests/unimplemented_interface_c.out | 1 +
 vlib/v/checker/tests/unimplemented_interface_d.out | 1 +
 vlib/v/checker/tests/unimplemented_interface_e.out | 1 +
 vlib/v/checker/tests/unimplemented_interface_f.out | 1 +
 6 files changed, 8 insertions(+)

diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 489fa15e11..08725970f0 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1851,6 +1851,8 @@ fn (mut c Checker) type_implements(typ table.Type, inter_typ table.Type, pos tok
 		if method := typ_sym.find_method(imethod.name) {
 			msg := c.table.is_same_method(imethod, method)
 			if msg.len > 0 {
+				sig := c.table.fn_signature(imethod, skip_receiver: true)
+				c.add_error_detail('$inter_sym.name has `$sig`')
 				c.error('`$styp` incorrectly implements method `$imethod.name` of interface `$inter_sym.name`: $msg',
 					pos)
 				return false
@@ -4907,6 +4909,7 @@ pub fn (mut c Checker) map_init(mut node ast.MapInit) table.Type {
 	return map_type
 }
 
+// call this *before* calling error or warn
 pub fn (mut c Checker) add_error_detail(s string) {
 	c.error_details << s
 }
diff --git a/vlib/v/checker/tests/unimplemented_interface_b.out b/vlib/v/checker/tests/unimplemented_interface_b.out
index 9a95f12bf7..332f23214e 100644
--- a/vlib/v/checker/tests/unimplemented_interface_b.out
+++ b/vlib/v/checker/tests/unimplemented_interface_b.out
@@ -4,3 +4,4 @@ vlib/v/checker/tests/unimplemented_interface_b.vv:13:6: error: `Cat` incorrectly
    13 |     foo(c)
       |         ^
    14 | }
+details: main.Animal has `name() string`
diff --git a/vlib/v/checker/tests/unimplemented_interface_c.out b/vlib/v/checker/tests/unimplemented_interface_c.out
index 6c88e28201..c60a8facc2 100644
--- a/vlib/v/checker/tests/unimplemented_interface_c.out
+++ b/vlib/v/checker/tests/unimplemented_interface_c.out
@@ -4,3 +4,4 @@ vlib/v/checker/tests/unimplemented_interface_c.vv:12:6: error: `Cat` incorrectly
    12 |     foo(Cat{})
       |         ~~~~~
    13 | }
+details: main.Animal has `name()`
diff --git a/vlib/v/checker/tests/unimplemented_interface_d.out b/vlib/v/checker/tests/unimplemented_interface_d.out
index 506f7f51b0..c219ff8cd6 100644
--- a/vlib/v/checker/tests/unimplemented_interface_d.out
+++ b/vlib/v/checker/tests/unimplemented_interface_d.out
@@ -4,3 +4,4 @@ vlib/v/checker/tests/unimplemented_interface_d.vv:12:6: error: `Cat` incorrectly
    12 |     foo(Cat{})
       |         ~~~~~
    13 | }
+details: main.Animal has `speak(s string)`
diff --git a/vlib/v/checker/tests/unimplemented_interface_e.out b/vlib/v/checker/tests/unimplemented_interface_e.out
index b240dd4c81..49d1fe3512 100644
--- a/vlib/v/checker/tests/unimplemented_interface_e.out
+++ b/vlib/v/checker/tests/unimplemented_interface_e.out
@@ -4,3 +4,4 @@ vlib/v/checker/tests/unimplemented_interface_e.vv:12:6: error: `Cat` incorrectly
    12 |     foo(Cat{})
       |         ~~~~~
    13 | }
+details: main.Animal has `speak(s string)`
diff --git a/vlib/v/checker/tests/unimplemented_interface_f.out b/vlib/v/checker/tests/unimplemented_interface_f.out
index 9ed8bec110..58b29e1fbf 100644
--- a/vlib/v/checker/tests/unimplemented_interface_f.out
+++ b/vlib/v/checker/tests/unimplemented_interface_f.out
@@ -4,3 +4,4 @@ vlib/v/checker/tests/unimplemented_interface_f.vv:11:13: error: `Cat` incorrectl
    11 |     animals << Cat{}
       |                ~~~~~
    12 | }
+details: main.Animal has `speak(s string)`