RFC: Fix skipchars inexact error/hanging (#16892) (#18752)

* Fix skipchars inexact error (#16892)

* fix indent ((squash))

* add parentheses to test_skipchars macrocalls ((squash))

The whitespace separating strings containing whitespace was hurting my eyes.

* Remove now unused unexported function peekchar

And its friend, the _chtmp const.

* Make Char(0xffffffff) as a possible value for the linecomment argument ((squash))

* change `action` argument name to `skipcomment` ((squash))

* Simplify function

* Restore peekchar

* Remove support for IOBuffer

* Trailling whitespace + typo

Author: fcard

base/iostream.jl

@@ -312,7 +312,7 @@ end
 const _chtmp = Array{Char}(1)
 function peekchar(s::IOStream)
     if ccall(:ios_peekutf8, Cint, (Ptr{Void}, Ptr{Char}), s, _chtmp) < 0
-        return Char(-1)
+        return typemax(Char)
     end
     return _chtmp[1]
 end
@@ -321,15 +321,16 @@ function peek(s::IOStream)
     ccall(:ios_peekc, Cint, (Ptr{Void},), s)
 end
 
-function skipchars(s::IOStream, pred; linecomment::Char=Char(0xffffffff))
-    ch = peekchar(s); status = Int(ch)
-    while status >= 0 && (pred(ch) || ch == linecomment)
-        if ch == linecomment
-            readline(s)
-        else
-            read(s, Char)  # advance one character
+function skipchars(io::IOStream, pred; linecomment=nothing)
+    while !eof(io)
+        c = read(io, Char)
+        if c === linecomment
+            readline(io)
+        elseif !pred(c)
+            seek(io,position(io)-sizeof(string(c)))
+            break
         end
-        ch = peekchar(s); status = Int(ch)
     end
-    return s
+    return io
 end
+

test/choosetests.jl

@@ -35,7 +35,7 @@ function choosetests(choices = [])
         "enums", "cmdlineargs", "i18n", "workspace", "libdl", "int",
         "checked", "intset", "floatfuncs", "compile", "distributed", "inline",
         "boundscheck", "error", "ambiguous", "cartesian", "asmvariant", "osutils",
-        "channels"
+        "channels", "iostream"
     ]
     profile_skipped = false
     if startswith(string(Sys.ARCH), "arm")

test/iostream.jl

@@ -0,0 +1,31 @@
+# Test skipchars for IOStreams
+mktemp() do path, file
+    function append_to_file(str)
+        mark(file)
+        println(file, str)
+        flush(file)
+        reset(file)
+    end
+
+    # test it doesn't error on eof
+    @test skipchars(file, isspace) == file
+
+    # test if it correctly skips
+    append_to_file("    ")
+    @test eof(skipchars(file, isspace))
+
+    # test it correctly detects comment lines
+    append_to_file("#    \n   ")
+    @test eof(skipchars(file, isspace, linecomment='#'))
+
+    # test it stops at the appropriate time
+    append_to_file("   not a space")
+    @test skipchars(file, isspace) == file
+    @test !eof(file) && read(file, Char) == 'n'
+
+    # test it correctly ignores the contents of comment lines
+    append_to_file("  #not a space \n   not a space")
+    @test skipchars(file, isspace, linecomment='#') == file
+    @test !eof(file) && read(file, Char) == 'n'
+end
+