Kage: compilation panic on partial function expr

[Zyko0]

Ebitengine Version

v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• OpenBSD
• Android
• iOS
• Nintendo Switch
• PlayStation 5
• Xbox
• Web Browsers

Go Version (go version)

1.21.1

What steps will reproduce the problem?

Trying to compile:

func Fragment(dst vec4, src vec2, color vec4) vec4 {
  return vec4(0)+imageSrc3At
}

What is the expected result?

Compilation error

What happens instead?

Panic:

panic: runtime error: index out of range [0] with length 0

goroutine 51 [running]:
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parseExpr
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/expr.go:91
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parseStmt
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/stmt.go:348
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parseBlock
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/shader.go:934
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parseFunc
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/shader.go:840
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parseDecl
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/shader.go:452
github.com/hajimehoshi/ebiten/v2/internal/shader.(*compileState).parse
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/shader.go:339
github.com/hajimehoshi/ebiten/v2/internal/shader.Compile
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/shader/shader.go:207
github.com/hajimehoshi/ebiten/v2/internal/graphics.CompileShader
        github.com/hajimehoshi/ebiten/v2@v2.8.0-alpha.1.0.20240512060738-5bb060b1e9a9/internal/graphics/shader.go:191
github.com/hajimehoshi/ebiten/v2.NewShader

Anything else you feel useful to add?

Not completely related, but this is a valid program, and prob shouldn't:

func Fragment(dst vec4, src vec2, color vec4) vec4 {
  return vec4(1, 0, 0, 1)
  return imageSrc3At // does nothing
}