Enable support for NO_COLOR and FORCE_COLOR environment variables (…

…#53742)

NEWS.md

@@ -36,6 +36,9 @@ Command-line option changes
 
 * The `-m/--module` flag can be passed to run the `main` function inside a package with a set of arguments.
   This `main` function should be declared using `@main` to indicate that it is an entry point.
+* Enabling or disabling color text in Julia can now be controlled with the
+[`NO_COLOR`](https://no-color.org/) or [`FORCE_COLOR`](https://force-color.org/) environment
+variables. ([#53742]).
 
 Multi-threading changes
 -----------------------

base/client.jl

@@ -229,7 +229,7 @@ incomplete_tag(exc::Meta.ParseError) = incomplete_tag(exc.detail)
 cmd_suppresses_program(cmd) = cmd in ('e', 'E')
 function exec_options(opts)
     startup               = (opts.startupfile != 2)
-    global have_color     = (opts.color != 0) ? (opts.color == 1) : nothing # --color=on
+    global have_color     = colored_text(opts)
     global is_interactive = (opts.isinteractive != 0)
 
     # pre-process command line argument list
@@ -419,7 +419,7 @@ end
 global active_repl
 
 # run the requested sort of evaluation loop on stdio
-function run_main_repl(interactive::Bool, quiet::Bool, banner::Symbol, history_file::Bool, color_set::Bool)
+function run_main_repl(interactive::Bool, quiet::Bool, banner::Symbol, history_file::Bool)
     fallback_repl = parse(Bool, get(ENV, "JULIA_FALLBACK_REPL", "false"))
     if !fallback_repl && interactive
         load_InteractiveUtils()
@@ -565,8 +565,7 @@ function repl_main(_)
 
     quiet                 = (opts.quiet != 0)
     history_file          = (opts.historyfile != 0)
-    color_set             = (opts.color != 0) # --color!=auto
-    return run_main_repl(interactiveinput, quiet, banner, history_file, color_set)
+    return run_main_repl(interactiveinput, quiet, banner, history_file)
 end
 
 """

base/libuv.jl

@@ -138,13 +138,13 @@ function reinit_stdio()
     global stdout = init_stdio(ccall(:jl_stdout_stream, Ptr{Cvoid}, ()))::IO
     global stderr = init_stdio(ccall(:jl_stderr_stream, Ptr{Cvoid}, ()))::IO
     opts = JLOptions()
-    if opts.color != 0
-        have_color = (opts.color == 1)
+    color = colored_text(opts)
+    if !isnothing(color)
         if !isa(stdout, TTY)
-            global stdout = IOContext(stdout, :color => have_color)
+            global stdout = IOContext(stdout, :color => color::Bool)
         end
         if !isa(stderr, TTY)
-            global stderr = IOContext(stderr, :color => have_color)
+            global stderr = IOContext(stderr, :color => color::Bool)
         end
     end
     nothing

base/options.jl

@@ -67,6 +67,18 @@ end
 
 JLOptions() = unsafe_load(cglobal(:jl_options, JLOptions))
 
+function colored_text(opts::JLOptions)
+    return if opts.color != 0
+        opts.color == 1
+    elseif !isempty(get(ENV, "FORCE_COLOR", ""))
+        true
+    elseif !isempty(get(ENV, "NO_COLOR", ""))
+        false
+    else
+        nothing
+    end
+end
+
 function show(io::IO, opt::JLOptions)
     print(io, "JLOptions(")
     fields = fieldnames(JLOptions)

doc/src/manual/environment-variables.md

@@ -376,7 +376,7 @@ affinitized. Otherwise, Julia lets the operating system handle thread policy.
 ## REPL formatting
 
 Environment variables that determine how REPL output should be formatted at the
-terminal. Generally, these variables should be set to [ANSI terminal escape
+terminal. The `JULIA_*_COLOR` variables should be set to [ANSI terminal escape
 sequences](https://en.wikipedia.org/wiki/ANSI_escape_code). Julia provides
 a high-level interface with much of the same functionality; see the section on
 [The Julia REPL](@ref).
@@ -406,6 +406,19 @@ should have at the terminal.
 The formatting `Base.answer_color()` (default: normal, `"\033[0m"`) that output
 should have at the terminal.
 
+### [`NO_COLOR`](@id NO_COLOR)
+
+When this variable is present and not an empty string (regardless of its value) then colored
+text will be disabled on the REPL. Can be overridden with the flag `--color=yes` or with the
+environment variable [`FORCE_COLOR`](@ref FORCE_COLOR). This environment variable is
+[commonly recognized by command-line applications](https://no-color.org/).
+
+### [`FORCE_COLOR`](@id FORCE_COLOR)
+
+When this variable is present and not an empty string (regardless of its value) then
+colored text will be enabled on the REPL. Can be overridden with the flag `--color=no`. This
+environment variable is [commonly recognized by command-line applications](https://force-color.org/).
+
 ## System and Package Image Building
 
 ### [`JULIA_CPU_TARGET`](@id JULIA_CPU_TARGET)

test/cmdlineargs.jl

@@ -429,9 +429,30 @@ let exename = `$(Base.julia_cmd()) --startup-file=no --color=no`
     @test readchomp(`$exename -E "isinteractive()" -i`) == "true"
 
     # --color
-    @test readchomp(`$exename --color=yes -E "Base.have_color"`) == "true"
-    @test readchomp(`$exename --color=no -E "Base.have_color"`) == "false"
-    @test errors_not_signals(`$exename --color=false`)
+    function color_cmd(; flag, no_color=nothing, force_color=nothing)
+        cmd = `$exename --color=$flag -E "Base.have_color"`
+        return addenv(cmd, "NO_COLOR" => no_color, "FORCE_COLOR" => force_color)
+    end
+
+    @test readchomp(color_cmd(flag="auto")) == "nothing"
+    @test readchomp(color_cmd(flag="no")) == "false"
+    @test readchomp(color_cmd(flag="yes")) == "true"
+    @test errors_not_signals(color_cmd(flag="false"))
+    @test errors_not_signals(color_cmd(flag="true"))
+
+    @test readchomp(color_cmd(flag="auto", no_color="")) == "nothing"
+    @test readchomp(color_cmd(flag="auto", no_color="1")) == "false"
+    @test readchomp(color_cmd(flag="no", no_color="1")) == "false"
+    @test readchomp(color_cmd(flag="yes", no_color="1")) == "true"
+
+    @test readchomp(color_cmd(flag="auto", force_color="")) == "nothing"
+    @test readchomp(color_cmd(flag="auto", force_color="1")) == "true"
+    @test readchomp(color_cmd(flag="no", force_color="1")) == "false"
+    @test readchomp(color_cmd(flag="yes", force_color="1")) == "true"
+
+    @test readchomp(color_cmd(flag="auto", no_color="1", force_color="1")) == "true"
+    @test readchomp(color_cmd(flag="no", no_color="1", force_color="1")) == "false"
+    @test readchomp(color_cmd(flag="yes", no_color="1", force_color="1")) == "true"
 
     # --history-file
     @test readchomp(`$exename -E "Bool(Base.JLOptions().historyfile)"