checker: avert if else is unnecessary

vlib/log/log.v

@@ -21,7 +21,6 @@ fn tag(l Level) string {
 		.warn  { term.yellow('WARN ') }
 		.info  { term.white('INFO ') }
 		.debug { term.blue('DEBUG') }
-		else { '     ' }
 	}
 }
 

vlib/time/format.v

@@ -150,8 +150,7 @@ mut 	res := match fmt_date {
 		.space{
 			' '
 		}
-		else {
-			'unknown enumeration $fmt_dlmtr'}})
+	})
 	return res
 }
 

vlib/v/builder/compile.v

@@ -42,10 +42,6 @@ pub fn compile(command string, pref &pref.Preferences) {
 		.x64 {
 			b.compile_x64()
 		}
-		else {
-			eprintln('backend not implemented `$pref.backend`')
-			exit(1)
-		}
 	}
 	if pref.is_stats {
 		tmark.stop()

vlib/v/checker/checker.v

@@ -1601,46 +1601,57 @@ fn (mut c Checker) match_exprs(node mut ast.MatchExpr, type_sym table.TypeSymbol
 	// this is achieved either by putting an else
 	// or, when the match is on a sum type or an enum
 	// by listing all variants or values
-	if !node.branches[node.branches.len - 1].is_else {
+	mut is_exhaustive := true
+	mut unhandled := []string
+	match type_sym.info {
+		table.SumType {
+			for v in it.variants {
+				v_str := c.table.type_to_str(v)
+				if v_str !in branch_exprs {
+					is_exhaustive = false
+					unhandled << '`$v_str`'
+				}
+			}
+		}
+		table.Enum {
+			for v in it.vals {
+				if v !in branch_exprs {
+					is_exhaustive = false
+					unhandled << '`.$v`'
+				}
+			}
+		}
+		else {
+			is_exhaustive = false
+		}
+	}
+	mut else_branch := node.branches[node.branches.len - 1]
+	mut has_else := else_branch.is_else
+	if !has_else {
 		for i, branch in node.branches {
 			if branch.is_else && i != node.branches.len - 1 {
 				c.error('`else` must be the last branch of `match`', branch.pos)
-				return
+				else_branch = branch
+				has_else = true
 			}
 		}
-		mut err := false
-		mut err_details := 'match must be exhaustive'
-		unhandled := []string
-		match type_sym.info {
-			table.SumType {
-				for v in it.variants {
-					v_str := c.table.type_to_str(v)
-					if v_str !in branch_exprs {
-						err = true
-						unhandled << '`$v_str`'
-					}
-				}
-			}
-			table.Enum {
-				for v in it.vals {
-					if v !in branch_exprs {
-						err = true
-						unhandled << '`.$v`'
-					}
-				}
-			}
-			else {
-				println('else')
-				err = true
-			}
-		}
-		if err {
-			if unhandled.len > 0 {
-				err_details += ' (add match branches for: ' + unhandled.join(', ') + ' or `else {}` at the end)'
-			}
-			c.error(err_details, node.pos)
-		}
 	}
+	if is_exhaustive {
+		if has_else {
+			c.error('match expression is exhaustive, `else` is unnecessary', else_branch.pos)
+		}
+		return
+	}
+	if has_else {
+		return
+	}
+	mut err_details := 'match must be exhaustive'
+	if unhandled.len > 0 {
+		err_details += ' (add match branches for: ' + unhandled.join(', ') + ' or `else {}` at the end)'
+	} else {
+		err_details += ' (add `else {}` at the end)'
+	}
+	c.error(err_details, node.pos)
 }
 
 pub fn (mut c Checker) if_expr(node mut ast.IfExpr) table.Type {

vlib/v/checker/tests/inout/match_expr_else.out

@@ -5,3 +5,17 @@ vlib/v/checker/tests/inout/match_expr_else.v:5:6: error: match must be exhaustiv
                ~~~~~~~~~
     6|         int {
     7|             'int'
+vlib/v/checker/tests/inout/match_expr_else.v:23:3: error: match expression is exhaustive, `else` is unnecessary
+   21|             'f64'
+   22|         }
+   23|         else {
+               ~~~~~~
+   24|             'else'
+   25|         }
+vlib/v/checker/tests/inout/match_expr_else.v:34:3: error: `else` must be the last branch of `match`
+   32|             'string'
+   33|         }
+   34|         else {
+               ~~~~~~
+   35|             'else'
+   36|         }

vlib/v/checker/tests/inout/match_expr_else.vv

@@ -10,4 +10,32 @@ fn main() {
 			'string'
 		}
 	}
+	_ := match x {
+		int {
+			'int'
+		}
+		string {
+			'string'
+		}
+		f64 {
+			'f64'
+		}
+		else {
+			'else'
+		}
+	}
+	_ := match x {
+		int {
+			'int'
+		}
+		string {
+			'string'
+		}
+		else {
+			'else'
+		}
+		f64 {
+			'f64'
+		}
+	}
 }

vlib/v/pref/os.v

@@ -107,11 +107,6 @@ pub fn (o OS) str() string {
 		.haiku {
 			return 'Haiku'
 		}
-		else {
-			//TODO Remove when V is smart enough to know that there's no other possibilities
-			//should never be reached as all enum types have been enumerated
-			panic('unknown OS enum type: $o')
-		}
 	}
 }
 

vlib/v/tests/match_expression_for_types_test.v

@@ -55,10 +55,6 @@ fn test_match_expression_on_sumtype_full(){
 			c = 2
 			eprintln('hi')
 			'a string'
-		}else{
-			c = 3
-			eprintln('hi')
-			'unknown'
 		}
 	}
 	assert res == 'an integer'