checker: improve error message for match branch type mismatch (#6588)

vlib/v/checker/checker.v

@@ -3173,7 +3173,7 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, type_sym table.TypeSymbol
 			} else if !c.check_types(expr_type, c.expected_type) {
 				expr_str := c.table.type_to_str(expr_type)
 				expect_str := c.table.type_to_str(c.expected_type)
-				c.error('cannot use type `$expect_str` as type `$expr_str`', node.pos)
+				c.error('cannot match `$expr_str` with `$expect_str` condition', branch.pos)
 			}
 			branch_exprs[key] = val + 1
 		}

vlib/v/checker/tests/match_expr_and_expected_type_error.out

@@ -1,13 +1,14 @@
-vlib/v/checker/tests/match_expr_and_expected_type_error.vv:2:1: error: cannot use type `rune` as type `string`
+vlib/v/checker/tests/match_expr_and_expected_type_error.vv:3:3: error: cannot match `string` with `rune` condition
     1 | ch := `a`
     2 | match ch {
-      | ~~~~~~~~~~
     3 |   'a' {}
+      |   ~~~~~
     4 |   else {}
-vlib/v/checker/tests/match_expr_and_expected_type_error.vv:8:1: error: cannot use type `int` as type `string`
+    5 | }
-    6 | 
+vlib/v/checker/tests/match_expr_and_expected_type_error.vv:9:3: error: cannot match `string` with `int` condition
-    7 | char := 123
+    7 | i := 123
-    8 | match char {
+    8 | match i {
-      | ~~~~~~~~~~~~
     9 |   'a' {}
+      |   ~~~~~
    10 |   else {}
+   11 | }

vlib/v/checker/tests/match_expr_and_expected_type_error.vv

@@ -4,8 +4,8 @@ match ch {
   else {}
 }
 
-char := 123
+i := 123
-match char {
+match i {
   'a' {}
   else {}
 }

vlib/v/checker/tests/match_invalid_type.out

@@ -0,0 +1,21 @@
+vlib/v/checker/tests/match_invalid_type.vv:5:3: error: cannot match `byte` with `IoS` condition
+    3 | fn sum() {
+    4 |     match IoS(1) {
+    5 |         byte {
+      |         ~~~~~~
+    6 |             println('not cool')
+    7 |         }
+vlib/v/checker/tests/match_invalid_type.vv:4:2: error: match must be exhaustive (add match branches for: `int`, `string` or `else {}` at the end)
+    2 |
+    3 | fn sum() {
+    4 |     match IoS(1) {
+      |     ~~~~~~~~~~~~~~
+    5 |         byte {
+    6 |             println('not cool')
+vlib/v/checker/tests/match_invalid_type.vv:24:3: error: `Cat` doesn't implement method `speak`
+   22 |     a := Animal(Dog{})
+   23 |     match a {
+   24 |         Cat {
+      |         ~~~~~
+   25 |             println('not cool either')
+   26 |         }

vlib/v/checker/tests/match_invalid_type.vv

@@ -1,5 +1,13 @@
 type IoS = int | string
 
+fn sum() {
+	match IoS(1) {
+		byte {
+			println('not cool')
+		}
+	}
+}
+
 interface Animal {
 	speak()
 }
@@ -10,12 +18,7 @@ fn (d Dog) speak() {}
 
 struct Cat {}
 
-fn main() {
+fn iface() {
-	match IoS(1) {
-		byte {
-			println('not cool')
-		}
-	}
 	a := Animal(Dog{})
 	match a {
 		Cat {

vlib/v/checker/tests/match_sumtype_type_invalid.out

@@ -1,14 +0,0 @@
-vlib/v/checker/tests/match_sumtype_type_invalid.vv:14:2: error: cannot use type `IoS` as type `byte`
-   12 |
-   13 | fn main() {
-   14 |     match IoS(1) {
-      |     ~~~~~~~~~~~~~~
-   15 |         byte {
-   16 |             println('not cool')
-vlib/v/checker/tests/match_sumtype_type_invalid.vv:21:3: error: `Cat` doesn't implement method `speak`
-   19 |     a := Animal(Dog{})
-   20 |     match a {
-   21 |         Cat {
-      |         ~~~~~
-   22 |             println('not cool either')
-   23 |         }

vlib/v/checker/tests/match_undefined_cond.out

@@ -5,3 +5,17 @@ vlib/v/checker/tests/match_undefined_cond.vv:4:15: error: undefined ident: `Asd`
       |                  ~~~
     5 |         1 { 'foo' }
     6 |         2 { 'test' }
+vlib/v/checker/tests/match_undefined_cond.vv:5:3: error: cannot match `any_int` with `void` condition
+    3 | fn main() {
+    4 |     res := match Asd {
+    5 |         1 { 'foo' }
+      |         ~~~
+    6 |         2 { 'test' }
+    7 |         else { '' }
+vlib/v/checker/tests/match_undefined_cond.vv:6:3: error: cannot match `any_int` with `void` condition
+    4 |     res := match Asd {
+    5 |         1 { 'foo' }
+    6 |         2 { 'test' }
+      |         ~~~
+    7 |         else { '' }
+    8 |     }