deprecate const on local variables, which used to be ignored.

part of #5148

NEWS.md

@@ -63,6 +63,9 @@ Language changes
     (`need_to_handle_undef_sparam = Set{Any}(m.sig for m in Test.detect_unbound_args(Base, recursive=true))`)
     is equal (`==`) to some known set (`expected = Set()`). ([#23117])
 
+  * `const` declarations on local variables were previously ignored. They now give a
+    warning, so that this syntax can be disallowed or given a new meaning in a
+    future version ([#5148]).
 
 Breaking changes
 ----------------

base/complex.jl

@@ -499,9 +499,9 @@ julia> rad2deg(angle(-1 - im))
 angle(z::Complex) = atan2(imag(z), real(z))
 
 function log(z::Complex{T}) where T<:AbstractFloat
-    const T1::T  = 1.25
-    const T2::T  = 3
-    const ln2::T = log(convert(T,2))  #0.6931471805599453
+    T1::T  = 1.25
+    T2::T  = 3
+    ln2::T = log(convert(T,2))  #0.6931471805599453
     x, y = reim(z)
     ρ, k = ssqs(x,y)
     ax = abs(x)
@@ -835,7 +835,7 @@ function cosh(z::Complex)
 end
 
 function tanh(z::Complex{T}) where T<:AbstractFloat
-    const Ω = prevfloat(typemax(T))
+    Ω = prevfloat(typemax(T))
     ξ, η = reim(z)
     if isnan(ξ) && η==0 return Complex(ξ, η) end
     if 4*abs(ξ) > asinh(Ω) #Overflow?
@@ -880,9 +880,9 @@ function acosh(z::Complex)
 end
 
 function atanh(z::Complex{T}) where T<:AbstractFloat
-    const Ω = prevfloat(typemax(T))
-    const θ = sqrt(Ω)/4
-    const ρ = 1/θ
+    Ω = prevfloat(typemax(T))
+    θ = sqrt(Ω)/4
+    ρ = 1/θ
     x, y = reim(z)
     ax = abs(x)
     ay = abs(y)

base/libc.jl

@@ -39,7 +39,7 @@ if Sys.iswindows()
     function dup(src::WindowsRawSocket)
         new_handle = Ref{Ptr{Void}}(-1)
         my_process = ccall(:GetCurrentProcess, stdcall, Ptr{Void}, ())
-        const DUPLICATE_SAME_ACCESS = 0x2
+        DUPLICATE_SAME_ACCESS = 0x2
         status = ccall(:DuplicateHandle, stdcall, Int32,
             (Ptr{Void}, Ptr{Void}, Ptr{Void}, Ptr{Ptr{Void}}, UInt32, Int32, UInt32),
             my_process, src.handle, my_process, new_handle, 0, false, DUPLICATE_SAME_ACCESS)
@@ -290,10 +290,10 @@ if Sys.iswindows()
     GetLastError() = ccall(:GetLastError, stdcall, UInt32, ())
 
     function FormatMessage(e=GetLastError())
-        const FORMAT_MESSAGE_ALLOCATE_BUFFER = UInt32(0x100)
-        const FORMAT_MESSAGE_FROM_SYSTEM = UInt32(0x1000)
-        const FORMAT_MESSAGE_IGNORE_INSERTS = UInt32(0x200)
-        const FORMAT_MESSAGE_MAX_WIDTH_MASK = UInt32(0xFF)
+        FORMAT_MESSAGE_ALLOCATE_BUFFER = UInt32(0x100)
+        FORMAT_MESSAGE_FROM_SYSTEM = UInt32(0x1000)
+        FORMAT_MESSAGE_IGNORE_INSERTS = UInt32(0x200)
+        FORMAT_MESSAGE_MAX_WIDTH_MASK = UInt32(0xFF)
         lpMsgBuf = Ref{Ptr{UInt16}}()
         lpMsgBuf[] = 0
         len = ccall(:FormatMessageW, stdcall, UInt32, (Cint, Ptr{Void}, Cint, Cint, Ptr{Ptr{UInt16}}, Cint, Ptr{Void}),

base/libdl.jl

@@ -234,8 +234,8 @@ function dllist()
     dynamic_libraries = Vector{AbstractString}(0)
 
     @static if Sys.islinux()
-        const callback = cfunction(dl_phdr_info_callback, Cint,
-                                   Tuple{Ref{dl_phdr_info}, Csize_t, Ref{Vector{AbstractString}}})
+        callback = cfunction(dl_phdr_info_callback, Cint,
+                             Tuple{Ref{dl_phdr_info}, Csize_t, Ref{Vector{AbstractString}}})
         ccall(:dl_iterate_phdr, Cint, (Ptr{Void}, Ref{Vector{AbstractString}}), callback, dynamic_libraries)
     end
 
@@ -254,8 +254,8 @@ function dllist()
     end
 
     @static if Sys.isbsd() && !Sys.isapple()
-        const callback = cfunction(dl_phdr_info_callback, Cint,
-                                   Tuple{Ref{dl_phdr_info}, Csize_t, Ref{Vector{AbstractString}}})
+        callback = cfunction(dl_phdr_info_callback, Cint,
+                             Tuple{Ref{dl_phdr_info}, Csize_t, Ref{Vector{AbstractString}}})
         ccall(:dl_iterate_phdr, Cint, (Ptr{Void}, Ref{Vector{AbstractString}}), callback, dynamic_libraries)
         shift!(dynamic_libraries)
     end

base/loading.jl

@@ -46,7 +46,7 @@ elseif Sys.isapple()
         isfile(path) || return false
         path_basename = String(basename(path))
         local casepreserved_basename
-        const header_size = 12
+        header_size = 12
         buf = Vector{UInt8}(length(path_basename) + header_size + 1)
         while true
             ret = ccall(:getattrlist, Cint,

base/math.jl

@@ -758,9 +758,9 @@ end
 @inline literal_pow(::typeof(^), x::Float16, ::Val{p}) where {p} = Float16(literal_pow(^,Float32(x),Val(p)))
 
 function angle_restrict_symm(theta)
-    const P1 = 4 * 7.8539812564849853515625e-01
-    const P2 = 4 * 3.7748947079307981766760e-08
-    const P3 = 4 * 2.6951514290790594840552e-15
+    P1 = 4 * 7.8539812564849853515625e-01
+    P2 = 4 * 3.7748947079307981766760e-08
+    P3 = 4 * 2.6951514290790594840552e-15
 
     y = 2*floor(theta/(2*pi))
     r = ((theta - y*P1) - y*P2) - y*P3

base/regex.jl

@@ -251,10 +251,10 @@ function _write_capture(io, re, group)
 end
 
 function _replace(io, repl_s::SubstitutionString, str, r, re)
-    const SUB_CHAR = '\\'
-    const GROUP_CHAR = 'g'
-    const LBRACKET = '<'
-    const RBRACKET = '>'
+    SUB_CHAR = '\\'
+    GROUP_CHAR = 'g'
+    LBRACKET = '<'
+    RBRACKET = '>'
     repl = repl_s.string
     i = start(repl)
     e = endof(repl)

base/repl/REPL.jl

@@ -807,7 +807,7 @@ function setup_interface(
         extra_repl_keymap = [extra_repl_keymap]
     end
 
-    const repl_keymap = AnyDict(
+    repl_keymap = AnyDict(
         ';' => function (s,o...)
             if isempty(s) || position(LineEdit.buffer(s)) == 0
                 buf = copy(LineEdit.buffer(s))

base/repl/REPLCompletions.jl

@@ -82,14 +82,15 @@ function complete_symbol(sym, ffunc)
     suggestions
 end
 
+const sorted_keywords = [
+    "abstract type", "baremodule", "begin", "break", "catch", "ccall",
+    "const", "continue", "do", "else", "elseif", "end", "export", "false",
+    "finally", "for", "function", "global", "if", "import",
+    "importall", "let", "local", "macro", "module", "mutable struct",
+    "primitive type", "quote", "return", "struct",
+    "true", "try", "using", "while"]
+
 function complete_keyword(s::String)
-    const sorted_keywords = [
-        "abstract type", "baremodule", "begin", "break", "catch", "ccall",
-        "const", "continue", "do", "else", "elseif", "end", "export", "false",
-        "finally", "for", "function", "global", "if", "import",
-        "importall", "let", "local", "macro", "module", "mutable struct",
-        "primitive type", "quote", "return", "struct",
-        "true", "try", "using", "while"]
     r = searchsorted(sorted_keywords, s)
     i = first(r)
     n = length(sorted_keywords)

base/sparse/sparsematrix.jl

@@ -2042,8 +2042,8 @@ function getindex_I_sorted(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVector, J::Abst
 end
 
 function getindex_I_sorted_bsearch_A(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVector, J::AbstractVector) where {Tv,Ti}
-    const nI = length(I)
-    const nJ = length(J)
+    nI = length(I)
+    nJ = length(J)
 
     colptrA = A.colptr; rowvalA = A.rowval; nzvalA = A.nzval
     colptrS = Vector{Ti}(nJ+1)
@@ -2101,8 +2101,8 @@ function getindex_I_sorted_bsearch_A(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVecto
 end
 
 function getindex_I_sorted_linear(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVector, J::AbstractVector) where {Tv,Ti}
-    const nI = length(I)
-    const nJ = length(J)
+    nI = length(I)
+    nJ = length(J)
 
     colptrA = A.colptr; rowvalA = A.rowval; nzvalA = A.nzval
     colptrS = Vector{Ti}(nJ+1)
@@ -2160,8 +2160,8 @@ function getindex_I_sorted_linear(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVector,
 end
 
 function getindex_I_sorted_bsearch_I(A::SparseMatrixCSC{Tv,Ti}, I::AbstractVector, J::AbstractVector) where {Tv,Ti}
-    const nI = length(I)
-    const nJ = length(J)
+    nI = length(I)
+    nJ = length(J)
 
     colptrA = A.colptr; rowvalA = A.rowval; nzvalA = A.nzval
     colptrS = Vector{Ti}(nJ+1)

doc/src/manual/variables-and-scoping.md

@@ -475,7 +475,8 @@ their values (or even their types) might change at almost any time. If a global
 not change, adding a `const` declaration solves this performance problem.
 
 Local constants are quite different. The compiler is able to determine automatically when a local
-variable is constant, so local constant declarations are not necessary, and are currently just ignored.
+variable is constant, so local constant declarations are not necessary, and in fact are currently
+not supported.
 
 Special top-level assignments, such as those performed by the `function` and `struct` keywords,
 are constant by default.

src/julia-syntax.scm

@@ -1320,7 +1320,7 @@
         (if (null? params)
             (error (string "empty type parameter list in \"" (deparse `(= (curly ,name) ,type-ex)) "\"")))
         `(block
-          (const ,name)
+          (const-if-global ,name)
           ,(expand-forms
             `(= ,name (where ,type-ex ,@params)))))
       (expand-forms
@@ -3115,11 +3115,12 @@ f(x) = yt(x)
                  (if (vinfo:never-undef vi)
                      '(null)
                      `(newvar ,(cadr e))))))
-          ((const)
+          ((const) e)
+          ((const-if-global)
            (if (or (assq (cadr e) (car  (lam:vinfo lam)))
                    (assq (cadr e) (cadr (lam:vinfo lam))))
                '(null)
-               e))
+               `(const ,(cadr e))))
           ((isdefined) ;; convert isdefined expr to function for closure converted variables
            (let* ((sym (cadr e))
                   (vi (and (symbol? sym) (assq sym (car  (lam:vinfo lam)))))
@@ -3661,7 +3662,14 @@ f(x) = yt(x)
             ((local-def) #f)
             ((local) #f)
             ((implicit-global) #f)
-            ((const) (emit e))
+            ((const)
+             (if (or (assq (cadr e) (car  (lam:vinfo lam)))
+                     (assq (cadr e) (cadr (lam:vinfo lam))))
+                 (begin
+                   (syntax-deprecation #f (string "`const` declaration on local variable" (linenode-string current-loc))
+                                       "")
+                   '(null))
+                 (emit e)))
             ((isdefined) (if tail (emit-return e) e))
 
             ;; top level expressions returning values

test/TestHelpers.jl

@@ -24,8 +24,8 @@ function open_fake_pty()
         error("Unable to create a fake PTY in Windows")
     end
 
-    const O_RDWR = Base.Filesystem.JL_O_RDWR
-    const O_NOCTTY = Base.Filesystem.JL_O_NOCTTY
+    O_RDWR = Base.Filesystem.JL_O_RDWR
+    O_NOCTTY = Base.Filesystem.JL_O_NOCTTY
 
     fdm = ccall(:posix_openpt, Cint, (Cint,), O_RDWR|O_NOCTTY)
     fdm == -1 && error("Failed to open PTY master")

test/core.jl

@@ -438,7 +438,8 @@ function const_implies_local()
         x = 1
         local y
         let
-            const x = 0
+            # TODO: change back to `const` if that's ever allowed
+            local x = 0
             y = x
         end
         x, y
@@ -2055,11 +2056,11 @@ end
 
 # issue #8798
 let
-    const npy_typestrs = Dict("b1"=>Bool,
-                              "i1"=>Int8,      "u1"=>UInt8,
-                              "i2"=>Int16,     "u2"=>UInt16,
-                              "i4"=>Int32,     "u4"=>UInt32,
-                              "i8"=>Int64,     "u8"=>UInt64)
+    npy_typestrs = Dict("b1"=>Bool,
+                        "i1"=>Int8,      "u1"=>UInt8,
+                        "i2"=>Int16,     "u2"=>UInt16,
+                        "i4"=>Int32,     "u4"=>UInt32,
+                        "i8"=>Int64,     "u8"=>UInt64)
     sizeof_lookup() = sizeof(npy_typestrs["i8"])
     @test sizeof_lookup() == 8
 end

test/dates/io.jl

@@ -378,7 +378,7 @@ end
 
 # Issue: https://github.com/quinnj/TimeZones.jl/issues/19
 let
-    const Zulu = String
+    Zulu = String
 
     function Dates.tryparsenext(d::Dates.DatePart{'Z'}, str, i, len)
         Dates.tryparsenext_word(str, i, len, Dates.min_width(d), Dates.max_width(d))

test/misc.jl

@@ -576,7 +576,7 @@ if Sys.iswindows()
 
     let addr = cfunction(WeVirtualProtectThisToRWX, UInt64, (UInt64, UInt64))
         addr = addr-(UInt64(addr)%4096)
-        const PAGE_EXECUTE_READWRITE = 0x40
+        PAGE_EXECUTE_READWRITE = 0x40
         oldPerm = Ref{UInt32}()
         err18083 = ccall(:VirtualProtect,stdcall,Cint,
             (Ptr{Void}, Csize_t, UInt32, Ptr{UInt32}),

test/perf/shootout/binary_trees.jl

@@ -44,9 +44,9 @@ function loop_depths(d, min_depth, max_depth)
 end
 
 function binary_trees(N::Int=10)
-    const min_depth = 4
-    const max_depth = N
-    const stretch_depth = max_depth + 1
+    min_depth = 4
+    max_depth = N
+    stretch_depth = max_depth + 1
 
     # create and check stretch tree
     let c = check(make(0, stretch_depth))

test/perf/threads/lbm3d/lbm3d.jl

@@ -119,11 +119,11 @@ end
 precompile(calc_equi!, (Array{Float64,4}, Array{Float64,4}, Array{Float64,3}, Array{Float64,3}, Array{Float64,3}, Array{Float64,2}, Array{Float64,3}, Array{Float64,3}, Array{Float64,3}, Array{Float64,3}, Int64, Int64, Int64, Float64))
 
 function lbm3d(n)
-    const nx = n
-    const ny = nx
-    const nz = nx
-    const omega = 1.0
-    const density = 1.0
+    nx = n
+    ny = nx
+    nz = nx
+    omega = 1.0
+    density = 1.0
 
     # Implementation note: setting nchunk to nthreads() is a hack
     # to simulate the previous implementation's use of parallel regions.

test/perf/threads/stockcorr/pstockcorr.jl

@@ -61,15 +61,15 @@ end
 # Threaded version
 function pstockcorr(n)
     ## Correlated asset information
-    const CurrentPrice = [78. 102.]     # Initial Prices of the two stocks
-    const Corr = [1. 0.4; 0.4 1.]       # Correlation Matrix
-    const T = 500                       # Number of days to simulate = 2years = 500days
-    const dt = 1/250                    # Time step (1year = 250days)
-    const Div=[0.01 0.01]               # Dividend
-    const Vol=[0.2 0.3]                 # Volatility
+    CurrentPrice = [78. 102.]     # Initial Prices of the two stocks
+    Corr = [1. 0.4; 0.4 1.]       # Correlation Matrix
+    T = 500                       # Number of days to simulate = 2years = 500days
+    dt = 1/250                    # Time step (1year = 250days)
+    Div=[0.01 0.01]               # Dividend
+    Vol=[0.2 0.3]                 # Volatility
 
     ## Market Information
-    const r = 0.03                      # Risk-free rate
+    r = 0.03                      # Risk-free rate
 
     ## Define storages
     SimulPriceA = zeros(T,n)            # Simulated Price of Asset A
@@ -78,7 +78,7 @@ function pstockcorr(n)
     SimulPriceB[1,:] = CurrentPrice[2]
 
     ## Generating the paths of stock prices by Geometric Brownian Motion
-    const UpperTriangle = full(chol(Corr))    # UpperTriangle Matrix by Cholesky decomposition
+    UpperTriangle = full(chol(Corr))    # UpperTriangle Matrix by Cholesky decomposition
 
     # Optimization: pre-allocate these for performance
     # NOTE: the new GC will hopefully fix this, but currently GC time

test/pkg.jl

@@ -480,7 +480,7 @@ temp_pkg_dir() do
                     nothingtodomsg) Pkg.update("Example")
 
         metadata_dir = Pkg.dir("METADATA")
-        const old_commit = "313bfaafa301e82d40574a778720e893c559a7e2"
+        old_commit = "313bfaafa301e82d40574a778720e893c559a7e2"
 
         # Force a METADATA rollback to an old version, so that we will install some
         # outdated versions of some packages and then update some of those
@@ -525,7 +525,7 @@ temp_pkg_dir() do
         Pkg.rm(package)  # Remove package if installed
 
         metadata_dir = Pkg.dir("METADATA")
-        const old_commit = "83ff7116e51fc9cdbd7e67affbd344b9f5c9dbf2"
+        old_commit = "83ff7116e51fc9cdbd7e67affbd344b9f5c9dbf2"
 
         # Reset METADATA to the second to last update of Example.jl
         LibGit2.with(LibGit2.GitRepo, metadata_dir) do repo

test/repl.jl

@@ -232,7 +232,7 @@ function AddCustomMode(repl, prompt)
     hp.mode_mapping[:foobar] = foobar_mode
     foobar_mode.hist = hp
 
-    const foobar_keymap = Dict{Any,Any}(
+    foobar_keymap = Dict{Any,Any}(
         '<' => function (s,args...)
             if isempty(s)
                 if !haskey(s.mode_state,foobar_mode)

test/replcompletions.jl

@@ -76,7 +76,7 @@ function temp_pkg_dir_noinit(fn::Function)
     # Used in tests below to set up and tear down a sandboxed package directory
     # Unlike the version in test/pkg.jl, this does not run Pkg.init so does not
     # clone METADATA (only pkg and libgit2-online tests should need internet access)
-    const tmpdir = joinpath(tempdir(),randstring())
+    tmpdir = joinpath(tempdir(),randstring())
     withenv("JULIA_PKGDIR" => tmpdir) do
         @test !isdir(Pkg.dir())
         try