From da71bced464e10482e7b24b4e3bc3376a9894cc7 Mon Sep 17 00:00:00 2001
From: StunxFS <56417208+StunxFS@users.noreply.github.com>
Date: Thu, 28 Apr 2022 15:35:16 -0400
Subject: [PATCH] transformer: minor optimization for `'string literal'.len`
 (#14207)

---
 vlib/v/gen/c/cgen.v                                       | 3 +--
 vlib/v/gen/c/testdata/README.md                           | 4 ++--
 vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have | 2 ++
 vlib/v/gen/c/testdata/strlit_len_optimization.out         | 2 ++
 vlib/v/gen/c/testdata/strlit_len_optimization.vv          | 6 ++++++
 vlib/v/transformer/transformer.v                          | 6 ++++++
 6 files changed, 19 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/strlit_len_optimization.out
 create mode 100644 vlib/v/gen/c/testdata/strlit_len_optimization.vv

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 69dd1d3339..afa429e04b 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/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('$info.size')
 		return
-	}
-	if sym.kind == .chan && (node.field_name == 'len' || node.field_name == 'closed') {
+	} else if sym.kind == .chan && (node.field_name == 'len' || node.field_name == 'closed') {
 		g.write('sync__Channel_${node.field_name}(')
 		g.expr(node.expr)
 		g.write(')')
diff --git a/vlib/v/gen/c/testdata/README.md b/vlib/v/gen/c/testdata/README.md
index 6cff11b48b..3787edc20e 100644
--- a/vlib/v/gen/c/testdata/README.md
+++ b/vlib/v/gen/c/testdata/README.md
@@ -1,8 +1,8 @@
 ## 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 
+coutput_test.v is a *test runner*, that checks whether the generated C
 source code matches *all* expectations, specified in *.c.must_have files,
 in the folder vlib/v/gen/c/testdata/ .
 
diff --git a/vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have b/vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have
new file mode 100644
index 0000000000..d541b43c1a
--- /dev/null
+++ b/vlib/v/gen/c/testdata/strlit_len_optimization.c.must_have
@@ -0,0 +1,2 @@
+int a = 5;
+int b = 7;
diff --git a/vlib/v/gen/c/testdata/strlit_len_optimization.out b/vlib/v/gen/c/testdata/strlit_len_optimization.out
new file mode 100644
index 0000000000..b3172d1242
--- /dev/null
+++ b/vlib/v/gen/c/testdata/strlit_len_optimization.out
@@ -0,0 +1,2 @@
+5
+7
diff --git a/vlib/v/gen/c/testdata/strlit_len_optimization.vv b/vlib/v/gen/c/testdata/strlit_len_optimization.vv
new file mode 100644
index 0000000000..5ecdf69201
--- /dev/null
+++ b/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)
+}
diff --git a/vlib/v/transformer/transformer.v b/vlib/v/transformer/transformer.v
index 6239237dfc..2ddf97629c 100644
--- a/vlib/v/transformer/transformer.v
+++ 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)