From e018509ba68976020bc5f6a4f21e64defbf55449 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@vlang.io>
Date: Wed, 9 Sep 2020 13:59:52 +0200
Subject: [PATCH] checker: test for unnecessary default struct field values

---
 vlib/strconv/f32_str.v                           |  6 +++---
 vlib/strconv/f64_str.v                           | 10 +++++-----
 vlib/v/checker/checker.v                         | 12 ++++++++++++
 vlib/v/checker/tests/struct_unneeded_default.out |  6 ++++++
 vlib/v/checker/tests/struct_unneeded_default.vv  |  7 +++++++
 5 files changed, 33 insertions(+), 8 deletions(-)
 create mode 100644 vlib/v/checker/tests/struct_unneeded_default.out
 create mode 100644 vlib/v/checker/tests/struct_unneeded_default.vv

diff --git a/vlib/strconv/f32_str.v b/vlib/strconv/f32_str.v
index 2717c00b6e..aaa6d64dff 100644
--- a/vlib/strconv/f32_str.v
+++ b/vlib/strconv/f32_str.v
@@ -22,14 +22,14 @@ module strconv
 // dec32 is a floating decimal type representing m * 10^e.
 struct Dec32 {
 mut:
-	m u32 = 0
-	e int = 0
+	m u32
+	e int
 }
 
 // support union for convert f32 to u32
 union Uf32 {
 mut:
-	f f32 = 0
+	f f32
 	u u32
 }
 
diff --git a/vlib/strconv/f64_str.v b/vlib/strconv/f64_str.v
index 86f531b076..ae718f81ef 100644
--- a/vlib/strconv/f64_str.v
+++ b/vlib/strconv/f64_str.v
@@ -21,21 +21,21 @@ module strconv
 
 struct Uint128 {
 mut:
-	lo u64 = u64(0)
-	hi u64 = u64(0)
+	lo u64
+	hi u64
 }
 
 // dec64 is a floating decimal type representing m * 10^e.
 struct Dec64 {
 mut:
-	m u64 = 0
-	e int = 0
+	m u64
+	e int
 }
 
 // support union for convert f64 to u64
 union Uf64 {
 mut:
-	f f64 = 0
+	f f64
 	u u64
 }
 
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index b2d94d96d2..4580fbb8dc 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -364,6 +364,18 @@ pub fn (mut c Checker) struct_decl(decl ast.StructDecl) {
 					'has type `$field_expr_type_sym.source_name`, but should be `$field_type_sym.source_name`',
 					field.default_expr.position())
 			}
+			// Check for unnecessary inits like ` = 0` and ` = ''`
+			if field.default_expr is ast.IntegerLiteral as x {
+				if x.val == '0' {
+					c.error('unnecessary default value of `0`: struct fields are zeroed by default',
+						field.pos)
+				}
+			} else if field.default_expr is ast.StringLiteral as x {
+				if x.val == "''" {
+					c.error("unnecessary default value of '': struct fields are zeroed by default",
+						field.pos)
+				}
+			}
 		}
 	}
 }
diff --git a/vlib/v/checker/tests/struct_unneeded_default.out b/vlib/v/checker/tests/struct_unneeded_default.out
new file mode 100644
index 0000000000..736f6a1dad
--- /dev/null
+++ b/vlib/v/checker/tests/struct_unneeded_default.out
@@ -0,0 +1,6 @@
+vlib/v/checker/tests/struct_unneeded_default.vv:2:2: error: unnecessary default value of `0`: struct fields are zeroed by default
+    1 | struct Test {
+    2 |     n int = 0
+      |     ~~~~~~
+    3 |     s string = ''
+    4 | }
diff --git a/vlib/v/checker/tests/struct_unneeded_default.vv b/vlib/v/checker/tests/struct_unneeded_default.vv
new file mode 100644
index 0000000000..93f94d0548
--- /dev/null
+++ b/vlib/v/checker/tests/struct_unneeded_default.vv
@@ -0,0 +1,7 @@
+struct Test {
+	n int = 0
+	s string = ''
+}
+
+fn main() {
+}