shader: Treat if's 'init' part correctly

Updates #1230

internal/shader/stmt.go

@@ -111,7 +111,22 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 			return nil, false
 		}
 	case *ast.IfStmt:
-		// TODO: Parse stmt.Init
+		if stmt.Init != nil {
+			init := stmt.Init
+			stmt.Init = nil
+			b, ok := cs.parseBlock(block, []ast.Stmt{init, stmt}, nil, nil)
+			if !ok {
+				return nil, false
+			}
+
+			stmts = append(stmts, shaderir.Stmt{
+				Type: shaderir.BlockStmt,
+				Blocks: []shaderir.Block{
+					b.ir,
+				},
+			})
+			return stmts, true
+		}
 
 		exprs, ts, ss, ok := cs.parseExpr(block, stmt.Cond)
 		if !ok {

internal/shader/testdata/if_init.expected.vs

@@ -0,0 +1,14 @@
+void F0(out vec2 l0) {
+	vec2 l1 = vec2(0);
+	l1 = vec2(0.0);
+	{
+		vec2 l2 = vec2(0);
+		l2 = vec2(1.0);
+		if (((l2).x) == (1.0)) {
+			l0 = l2;
+			return;
+		}
+	}
+	l0 = l1;
+	return;
+}

internal/shader/testdata/if_init.go

@@ -0,0 +1,9 @@
+package main
+
+func Foo() vec2 {
+	v := vec2(0)
+	if v := vec2(1); v.x == 1 {
+		return v
+	}
+	return v
+}