transformer: minor optimization for `'string literal'.len` (#14207)

vlib/v/gen/c/cgen.v

@@ -3267,8 +3267,7 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 		info := sym.info as ast.ArrayFixed
 		g.write('$info.size')
 		return
-	}
+	} else if sym.kind == .chan && (node.field_name == 'len' || node.field_name == 'closed') {
-	if sym.kind == .chan && (node.field_name == 'len' || node.field_name == 'closed') {
 		g.write('sync__Channel_${node.field_name}(')
 		g.expr(node.expr)
 		g.write(')')

vlib/v/gen/c/testdata/README.md

@@ -1,6 +1,6 @@
 ## Purpose: tests data for the output of V's C code generator
 
-## TLDR: `v vlib/v/gen/c/coutput_test.v`
+## TLDR: `v run vlib/v/gen/c/coutput_test.v`
 
 coutput_test.v is a *test runner*, that checks whether the generated C
 source code matches *all* expectations, specified in *.c.must_have files,

vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have

@@ -0,0 +1,2 @@
+int a = 5;
+int b = 7;

vlib/v/gen/c/testdata/strlit_len_optimization.out

@@ -0,0 +1,2 @@
+5
+7

vlib/v/gen/c/testdata/strlit_len_optimization.vv

@@ -0,0 +1,6 @@
+fn main() {
+	a := 'Vlang'.len
+	b := r'Vlang\n'.len
+	println(a)
+	println(b)
+}

vlib/v/transformer/transformer.v

@@ -636,6 +636,12 @@ pub fn (mut t Transformer) expr(mut node ast.Expr) ast.Expr {
 		}
 		ast.SelectorExpr {
 			node.expr = t.expr(mut node.expr)
+			if mut node.expr is ast.StringLiteral && node.field_name == 'len' {
+				return ast.IntegerLiteral{
+					val: node.expr.val.len.str()
+					pos: node.pos
+				}
+			}
 		}
 		ast.SizeOf {
 			node.expr = t.expr(mut node.expr)