implement getfield overloading (#24960)

New functions `Base.getproperty` and `Base.setproperty!`
can be overloaded to change the behavior of `x.p` and `x.p = v`,
respectively.

This forces inference constant propagation through get/setproperty,
since it is very likely this method will yield better information after specializing on the field name
(even if `convert` is too big to make us want to inline the generic version and trigger the heuristic normally).

closes #16195 (and thus also closes #16226)
fix #1974

Author: vtjnash

Diff for: NEWS.md

@@ -19,13 +19,13 @@ New language features
     iterated using `pairs(kw)`. `kw` can no longer contain multiple entries for the same
     argument name ([#4916]).
 
- * Custom infix operators can now be defined by appending Unicode
-   combining marks, primes, and sub/superscripts to other operators.
-   For example, `+̂ₐ″` is parsed as an infix operator with the same
-   precedence as `+` ([#22089]).
+  * Custom infix operators can now be defined by appending Unicode
+    combining marks, primes, and sub/superscripts to other operators.
+    For example, `+̂ₐ″` is parsed as an infix operator with the same
+    precedence as `+` ([#22089]).
 
- * The macro call syntax `@macroname[args]` is now available and is parsed
-   as `@macroname([args])` ([#23519]).
+  * The macro call syntax `@macroname[args]` is now available and is parsed
+    as `@macroname([args])` ([#23519]).
 
   * The construct `if @generated ...; else ...; end` can be used to provide both
     `@generated` and normal implementations of part of a function. Surrounding code
@@ -35,6 +35,9 @@ New language features
     missing values ([#24653]). It propagates through standard operators and mathematical functions,
     and implements three-valued logic, similar to SQLs `NULL` and R's `NA`.
 
+  * Field access via dot-syntax can now be overloaded by adding methods to
+    `Base.getproperty` and `Base.setproperty!` ([#1974]).
+
 Language changes
 ----------------
 

Diff for: base/array.jl

@@ -95,6 +95,12 @@ import Core: arraysize, arrayset, arrayref
 vect() = Vector{Any}()
 vect(X::T...) where {T} = T[ X[i] for i = 1:length(X) ]
 
+"""
+    vect(X...)
+
+Create a Vector with element type computed from the promote_typeof of the argument,
+containing the argument list.
+"""
 function vect(X...)
     T = promote_typeof(X...)
     #T[ X[i] for i=1:length(X) ]

Diff for: base/boot.jl

@@ -153,6 +153,9 @@ export
     # constants
     nothing, Main
 
+const getproperty = getfield
+const setproperty! = setfield!
+
 abstract type Number end
 abstract type Real     <: Number end
 abstract type AbstractFloat <: Real end

Diff for: base/coreimg.jl

@@ -1,9 +1,12 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
-Main.Core.eval(Main.Core, :(baremodule Inference
+getfield(getfield(Main, :Core), :eval)(getfield(Main, :Core), :(baremodule Inference
 using Core.Intrinsics
 import Core: print, println, show, write, unsafe_write, STDOUT, STDERR
 
+const getproperty = getfield
+const setproperty! = setfield!
+
 ccall(:jl_set_istopmod, Void, (Any, Bool), Inference, false)
 
 eval(x) = Core.eval(Inference, x)

Diff for: base/docs/basedocs.jl

@@ -1236,8 +1236,8 @@ tuple
 """
     getfield(value, name::Symbol)
 
-Extract a named field from a `value` of composite type. The syntax `a.b` calls
-`getfield(a, :b)`.
+Extract a named field from a `value` of composite type.
+See also [`getproperty`](@ref Base.getproperty).
 
 # Examples
 ```jldoctest
@@ -1256,8 +1256,9 @@ getfield
 """
     setfield!(value, name::Symbol, x)
 
-Assign `x` to a named field in `value` of composite type. The syntax `a.b = c` calls
-`setfield!(a, :b, c)`. `value` must be mutable.
+Assign `x` to a named field in `value` of composite type.
+The `value` must be mutable and `x` must be a subtype of `fieldtype(typeof(value), name)`.
+See also [`setproperty!`](@ref Base.setproperty!).
 
 # Examples
 ```jldoctest
@@ -1768,4 +1769,26 @@ The base library of Julia.
 """
 kw"Base"
 
+"""
+    typeassert(x, type)
+
+Throw a TypeError unless `x isa type`.
+The syntax `x::type` calls this function.
+"""
+typeassert
+
+"""
+    getproperty(value, name::Symbol)
+
+The syntax `a.b` calls `getproperty(a, :b)`.
+"""
+Base.getproperty
+
+"""
+    setproperty!(value, name::Symbol, x)
+
+The syntax `a.b = c` calls `setproperty!(a, :b, c)`.
+"""
+Base.setproperty!
+
 end

Diff for: base/exports.jl

@@ -899,6 +899,8 @@ export
 
 # types
     convert,
+    # getproperty,
+    # setproperty!,
     fieldoffset,
     fieldname,
     fieldnames,

Diff for: base/inference.jl

@@ -1961,7 +1961,7 @@ function abstract_call_gf_by_type(@nospecialize(f), argtypes::Vector{Any}, @nosp
         # if there's a possibility we could constant-propagate a better result
         # (hopefully without doing too much work), try to do that now
         # TODO: it feels like this could be better integrated into abstract_call_method / typeinf_edge
-        const_rettype = abstract_call_method_with_const_args(argtypes, applicable[1]::SimpleVector, sv)
+        const_rettype = abstract_call_method_with_const_args(f, argtypes, applicable[1]::SimpleVector, sv)
         if const_rettype ⊑ rettype
             # use the better result, if it's a refinement of rettype
             rettype = const_rettype
@@ -2020,7 +2020,7 @@ function cache_lookup(code::MethodInstance, argtypes::Vector{Any}, cache::Vector
     return nothing
 end
 
-function abstract_call_method_with_const_args(argtypes::Vector{Any}, match::SimpleVector, sv::InferenceState)
+function abstract_call_method_with_const_args(@nospecialize(f), argtypes::Vector{Any}, match::SimpleVector, sv::InferenceState)
     method = match[3]::Method
     nargs::Int = method.nargs
     method.isva && (nargs -= 1)
@@ -2053,11 +2053,14 @@ function abstract_call_method_with_const_args(argtypes::Vector{Any}, match::Simp
         end
     end
     if !cache_inlineable && !sv.params.aggressive_constant_propagation
-        # in this case, see if all of the arguments are constants
-        for i in 1:nargs
-            a = argtypes[i]
-            if !isa(a, Const) && !isconstType(a)
-                return Any
+        tm = _topmod(sv)
+        if !istopfunction(tm, f, :getproperty) && !istopfunction(tm, f, :setproperty!)
+            # in this case, see if all of the arguments are constants
+            for i in 1:nargs
+                a = argtypes[i]
+                if !isa(a, Const) && !isconstType(a)
+                    return Any
+                end
             end
         end
     end

Diff for: base/libgit2/gitcredential.jl

@@ -116,7 +116,7 @@ function Base.read!(io::IO, cred::GitCredential)
             # https://git-scm.com/docs/git-credential#git-credential-codeurlcode
             copy!(cred, parse(GitCredential, value))
         else
-            setfield!(cred, Symbol(key), String(value))
+            Base.setproperty!(cred, Symbol(key), String(value))
         end
     end
 

Diff for: base/show.jl

@@ -146,7 +146,7 @@ function show_default(io::IO, @nospecialize(x))
                 if !isdefined(x, f)
                     print(io, undef_ref_str)
                 else
-                    show(recur_io, getfield(x, f))
+                    show(recur_io, getfield(x, i))
                 end
                 if i < nf
                     print(io, ", ")

Diff for: base/sysimg.jl

@@ -5,6 +5,17 @@ baremodule Base
 using Core.Intrinsics
 ccall(:jl_set_istopmod, Void, (Any, Bool), Base, true)
 
+getproperty(x, f::Symbol) = getfield(x, f)
+setproperty!(x, f::Symbol, v) = setfield!(x, f, convert(fieldtype(typeof(x), f), v))
+
+# Try to help prevent users from shooting them-selves in the foot
+# with ambiguities by defining a few common and critical operations
+# (and these don't need the extra convert code)
+getproperty(x::Module, f::Symbol) = getfield(x, f)
+setproperty!(x::Module, f::Symbol, v) = setfield!(x, f, v)
+getproperty(x::Type, f::Symbol) = getfield(x, f)
+setproperty!(x::Type, f::Symbol, v) = setfield!(x, f, v)
+
 function include(mod::Module, path::AbstractString)
     local result
     if INCLUDE_STATE === 1

Diff for: doc/src/manual/functions.md

@@ -158,16 +158,18 @@ Under the name `f`, the function does not support infix notation, however.
 
 A few special expressions correspond to calls to functions with non-obvious names. These are:
 
-| Expression        | Calls                  |
-|:----------------- |:---------------------- |
-| `[A B C ...]`     | [`hcat`](@ref)       |
-| `[A; B; C; ...]`  | [`vcat`](@ref)       |
-| `[A B; C D; ...]` | [`hvcat`](@ref)      |
-| `A'`              | [`adjoint`](@ref) |
-| `A.'`             | [`transpose`](@ref)  |
-| `1:n`             | [`colon`](@ref)      |
-| `A[i]`            | [`getindex`](@ref)   |
-| `A[i]=x`          | [`setindex!`](@ref)  |
+| Expression        | Calls                   |
+|:----------------- |:----------------------- |
+| `[A B C ...]`     | [`hcat`](@ref)          |
+| `[A; B; C; ...]`  | [`vcat`](@ref)          |
+| `[A B; C D; ...]` | [`hvcat`](@ref)         |
+| `A'`              | [`adjoint`](@ref)       |
+| `A.'`             | [`transpose`](@ref)     |
+| `1:n`             | [`colon`](@ref)         |
+| `A[i]`            | [`getindex`](@ref)      |
+| `A[i] = x`        | [`setindex!`](@ref)     |
+| `A.n`             | [`getproperty`](@ref Base.getproperty) |
+| `A.n = x`         | [`setproperty!`](@ref Base.setproperty!) |
 
 ## [Anonymous Functions](@id man-anonymous-functions)
 

Diff for: doc/src/stdlib/arrays.md

@@ -119,6 +119,7 @@ Base.cat
 Base.vcat
 Base.hcat
 Base.hvcat
+Base.vect
 Base.flipdim
 Base.circshift
 Base.circshift!

Diff for: doc/src/stdlib/base.md

@@ -115,6 +115,7 @@ Base.isless
 Base.ifelse
 Base.lexcmp
 Base.lexless
+Core.typeassert
 Core.typeof
 Core.tuple
 Base.ntuple
@@ -124,6 +125,10 @@ Base.finalizer
 Base.finalize
 Base.copy
 Base.deepcopy
+Base.getproperty
+Base.setproperty!
+Core.getfield
+Core.setfield!
 Core.isdefined
 Base.@isdefined
 Base.convert
@@ -133,7 +138,7 @@ Base.widen
 Base.identity
 ```
 
-## Dealing with Types
+## Properties of Types
 
 ```@docs
 Base.supertype
@@ -150,8 +155,6 @@ Base.eps(::Type{<:AbstractFloat})
 Base.eps(::AbstractFloat)
 Base.promote_type
 Base.promote_rule
-Core.getfield
-Core.setfield!
 Base.fieldoffset
 Core.fieldtype
 Base.isimmutable

Diff for: doc/src/stdlib/punctuation.md

@@ -2,11 +2,11 @@
 
 Extended documentation for mathematical symbols & functions is [here](@ref math-ops).
 
-| symbol      | meaning                                                                                     |
-|:----------- |:------------------------------------------------------------------------------------------- |
+| symbol      | meaning                                                                                                                                         |
+|:----------- |:----------------------------------------------------------------------------------------------------------------------------------------------- |
 | `@m`        | invoke macro `m`; followed by space-separated expressions                                   |
-| `!`         | prefix "not" operator                                                                       |
-| `a!( )`     | at the end of a function name, `!` indicates that a function modifies its argument(s)       |
+| `!`         | prefix "not" (logical negation) operator                                                    |
+| `a!( )`     | at the end of a function name, `!` is used as a convention to indicate that a function modifies its argument(s) |
 | `#`         | begin single line comment                                                                   |
 | `#=`        | begin multi-line comment (these are nestable)                                               |
 | `=#`        | end multi-line comment                                                                      |
@@ -23,23 +23,23 @@ Extended documentation for mathematical symbols & functions is [here](@ref math-
 | `~`         | bitwise not operator                                                                        |
 | `\`         | backslash operator                                                                          |
 | `'`         | complex transpose operator Aᴴ                                                               |
-| `a[]`       | array indexing                                                                              |
-| `[,]`       | vertical concatenation                                                                      |
-| `[;]`       | also vertical concatenation                                                                 |
-| `[    ]`    | with space-separated expressions, horizontal concatenation                                  |
+| `a[]`       | array indexing (calling [`getindex`](@ref) or [`setindex!`](@ref))                          |
+| `[,]`       | vector literal constructor (calling [`vect`](@ref Base.vect))                               |
+| `[;]`       | vertical concatenation (calling [`vcat`](@ref) or [`hvcat`](@ref))                          |
+| `[    ]`    | with space-separated expressions, horizontal concatenation (calling [`hcat`](@ref) or [`hvcat`](@ref)) |
 | `T{ }`      | parametric type instantiation                                                               |
 | `;`         | statement separator                                                                         |
 | `,`         | separate function arguments or tuple components                                             |
-| `?`         | 3-argument conditional operator (conditional ? if_true : if_false)                          |
+| `?`         | 3-argument conditional operator (used like: `conditional ? if_true : if_false`)             |
 | `""`        | delimit string literals                                                                     |
 | `''`        | delimit character literals                                                                  |
 | ``` ` ` ``` | delimit external process (command) specifications                                           |
-| `...`       | splice arguments into a function call or declare a varargs function or type                 |
-| `.`         | access named fields in objects/modules, also prefixes elementwise operator/function calls   |
-| `a:b`       | range a, a+1, a+2, ..., b                                                                   |
-| `a:s:b`     | range a, a+s, a+2s, ..., b                                                                  |
-| `:`         | index an entire dimension (1:end)                                                           |
-| `::`        | type annotation, depending on context                                                       |
+| `...`       | splice arguments into a function call or declare a varargs function                         |
+| `.`         | access named fields in objects/modules (calling [`getproperty`](@ref Base.getproperty) or [`setproperty!`](@ref Base.setproperty!)), also prefixes elementwise function calls (calling [`broadcast`](@ref)) |
+| `a:b`       | range a, a+1, a+2, ..., b (calling [`colon`](@ref))                                         |
+| `a:s:b`     | range a, a+s, a+2s, ..., b (also calling [`colon`](@ref))                                   |
+| `:`         | index an entire dimension (1:endof), see [`Colon`](@ref))                                   |
+| `::`        | type annotation or [`typeassert`](@ref), depending on context                               |
 | `:( )`      | quoted expression                                                                           |
 | `:a`        | symbol a                                                                                    |
 | `<:`        | [`subtype operator`](@ref <:)                                                               |

Diff for: src/julia-syntax.scm

@@ -1752,7 +1752,7 @@
     (if (and (pair? e) (eq? (car e) '|.|))
         (let ((f (cadr e)) (x (caddr e)))
           (cond ((or (eq? (car x) 'quote) (eq? (car x) 'inert) (eq? (car x) '$))
-                 `(call (core getfield) ,f ,x))
+                 `(call (top getproperty) ,f ,x))
                 ((eq? (car x) 'tuple)
                  (make-fuse f (cdr x)))
                 (else
@@ -2039,10 +2039,12 @@
                 ,.(if (eq? aa a)   '() `((= ,aa ,(expand-forms a))))
                 ,.(if (eq? bb b)   '() `((= ,bb ,(expand-forms b))))
                 ,.(if (eq? rr rhs) '() `((= ,rr ,(expand-forms rhs))))
-                (call (core setfield!) ,aa ,bb
-                      (call (top convert)
-                            (call (core fieldtype) (call (core typeof) ,aa) ,bb)
-                            ,rr))
+                (call (top setproperty!) ,aa ,bb
+                      (if (call (top ===) (top setproperty!) (core setfield!))
+                          (call (top convert)
+                                (call (core fieldtype) (call (core typeof) ,aa) ,bb)
+                                ,rr)
+                          ,rr))
                 (unnecessary ,rr)))))
          ((tuple)
           ;; multiple assignment