meta.jl

# This file is a part of Julia. License is MIT: https://julialang.org/license

"""
Convenience functions for metaprogramming.
"""
module Meta

using ..CoreLogging

export quot,
       isexpr,
       show_sexpr,
       @dump

quot(ex) = Expr(:quote, ex)

isexpr(ex::Expr, head)          = ex.head === head
isexpr(ex::Expr, heads::Union{Set,Vector,Tuple}) = in(ex.head, heads)
isexpr(ex,       head)          = false

isexpr(ex,       head, n::Int)  = isexpr(ex, head) && length(ex.args) == n


# ---- show_sexpr: print an AST as an S-expression ----

show_sexpr(ex) = show_sexpr(stdout, ex)
show_sexpr(io::IO, ex) = show_sexpr(io, ex, 0)
show_sexpr(io::IO, ex, indent::Int) = show(io, ex)

const sexpr_indent_width = 2

function show_sexpr(io::IO, ex::QuoteNode, indent::Int)
    inner = indent + sexpr_indent_width
    print(io, "(:quote, #QuoteNode\n", " "^inner)
    show_sexpr(io, ex.value, inner)
    print(io, '\n', " "^indent, ')')
end
function show_sexpr(io::IO, ex::Expr, indent::Int)
    inner = indent + sexpr_indent_width
    print(io, '(')
    show_sexpr(io, ex.head, inner)
    for arg in ex.args
        print(io, ex.head === :block ? ",\n"*" "^inner : ", ")
        show_sexpr(io, arg, inner)
    end
    if isempty(ex.args); print(io, ",)")
    else print(io, (ex.head === :block ? "\n"*" "^indent : ""), ')')
    end
end

"""
    @dump expr

Show every part of the representation of the given expression. Equivalent to
[`dump(:(expr))`](@ref dump).
"""
macro dump(expr)
    dump(expr)
end

"""
    lower(m, x)

Takes the expression `x` and returns an equivalent expression in lowered form
for executing in module `m`.
See also [`code_lowered`](@ref).
"""
lower(m::Module, @nospecialize(x)) = ccall(:jl_expand, Any, (Any, Any), x, m)

"""
    @lower [m] x

Return lowered form of the expression `x` in module `m`.
By default `m` is the module in which the macro is called.
See also [`lower`](@ref).
"""
macro lower(code)
    return :(lower($__module__, $(QuoteNode(code))))
end
macro lower(mod, code)
    return :(lower($(esc(mod)), $(QuoteNode(code))))
end


## interface to parser ##

"""
    ParseError(msg)

The expression passed to the [`parse`](@ref) function could not be interpreted as a valid Julia
expression.
"""
struct ParseError <: Exception
    msg::AbstractString
end

"""
    parse(str, start; greedy=true, raise=true, depwarn=true)

Parse the expression string and return an expression (which could later be passed to eval
for execution). `start` is the index of the first character to start parsing. If `greedy` is
`true` (default), `parse` will try to consume as much input as it can; otherwise, it will
stop as soon as it has parsed a valid expression. Incomplete but otherwise syntactically
valid expressions will return `Expr(:incomplete, "(error message)")`. If `raise` is `true`
(default), syntax errors other than incomplete expressions will raise an error. If `raise`
is `false`, `parse` will return an expression that will raise an error upon evaluation. If
`depwarn` is `false`, deprecation warnings will be suppressed.

```jldoctest
julia> Meta.parse("x = 3, y = 5", 7)
(:(y = 5), 13)

julia> Meta.parse("x = 3, y = 5", 5)
(:((3, y) = 5), 13)
```
"""
function parse(str::AbstractString, pos::Int; greedy::Bool=true, raise::Bool=true,
               depwarn::Bool=true)
    # pos is one based byte offset.
    # returns (expr, end_pos). expr is () in case of parse error.
    bstr = String(str)
    # For now, assume all parser warnings are depwarns
    ex, pos = with_logger(depwarn ? current_logger() : NullLogger()) do
        ccall(:jl_parse_string, Any,
              (Ptr{UInt8}, Csize_t, Int32, Int32),
              bstr, sizeof(bstr), pos-1, greedy ? 1 : 0)
    end
    if raise && isa(ex,Expr) && ex.head === :error
        throw(ParseError(ex.args[1]))
    end
    if ex === ()
        raise && throw(ParseError("end of input"))
        ex = Expr(:error, "end of input")
    end
    return ex, pos+1 # C is zero-based, Julia is 1-based
end

"""
    parse(str; raise=true, depwarn=true)

Parse the expression string greedily, returning a single expression. An error is thrown if
there are additional characters after the first expression. If `raise` is `true` (default),
syntax errors will raise an error; otherwise, `parse` will return an expression that will
raise an error upon evaluation.  If `depwarn` is `false`, deprecation warnings will be
suppressed.

```jldoctest
julia> Meta.parse("x = 3")
:(x = 3)

julia> Meta.parse("x = ")
:($(Expr(:incomplete, "incomplete: premature end of input")))

julia> Meta.parse("1.0.2")
ERROR: Base.Meta.ParseError("invalid numeric constant \\\"1.0.\\\"")
Stacktrace:
[...]

julia> Meta.parse("1.0.2"; raise = false)
:($(Expr(:error, "invalid numeric constant \"1.0.\"")))
```
"""
function parse(str::AbstractString; raise::Bool=true, depwarn::Bool=true)
    ex, pos = parse(str, 1, greedy=true, raise=raise, depwarn=depwarn)
    if isa(ex,Expr) && ex.head === :error
        return ex
    end
    if !done(str, pos)
        raise && throw(ParseError("extra token after end of expression"))
        return Expr(:error, "extra token after end of expression")
    end
    return ex
end

end # module