Three valid scripts that translate but do not build: single-line bodies and na() of a string array #281

Summary

Each script below runs on TradingView. pineforge-codegen 1.9.0 either rejects it in the front end or emits C++ that clang cannot compile. Writing the function body on indented lines, using string(na) and initialising the array in the constructor builds and runs.

Case 1 is next to #230, which 1.9.0 fixes: the := form now builds, but a parameter read after the first comma is still unknown.

Versions

pineforge-codegen 1.9.0, pineforge-engine v1.9.0 (ec44968), Apple clang, macOS arm64. The errors come from the front end and from type checks on the generated C++, so they should not depend on the platform.

All three share this head and tail:

//@version=6
strategy('repro')
type Box
    array<string> items
// case body here
if bar_index == 5
    strategy.entry('L', strategy.long)

1. A parameter read after the first comma of a single-line body

var b = Box.new(array.new<string>())
add(Box x, string s) => array.push(x.items, s), x.items.size()
add(b, 'a')

<input>:6:49: Unknown variable 'x' — not a PineForge builtin or a declared variable.

add(Box x, string s) => x.items.push(s), 1 (the parameter only before the first comma) builds.

2. A string ternary with na as a single-line body returns double

var b = Box.new(array.new<string>())
take(Box x) => x.items.size() > 2 ? x.items.shift() : na
b.items.push('a')
take(b)

error: no viable conversion from returned value of type 'std::string' to function return type 'double'

The function's type seems to come from the na branch. string(na) in that branch builds.

3. na() of an array<string> field

var b = Box.new()
if na(b.items)
    b.items := array.new<string>()

error: no matching function for call to 'is_na' — the candidates in pineforge/na.hpp take double, an integral type or the UDT, none takes std::vector<std::string>.

Expected

All three build and run as on TradingView: the single-line body sees its parameters in every comma-separated statement, the function in case 2 returns string, and na() accepts any array reference.

Workaround

Write the body on indented lines, give the na branch its type (string(na)), and create the array in the constructor instead of testing it with na(). Each case was checked against a control that differs in that one place and builds.

cc @luisleo526