IO#gets should have same result regardless of #peek availability (c…

…rystal-lang#13882)

Co-authored-by: Sijawusz Pur Rahnama <[email protected]>

spec/std/io/io_spec.cr

@@ -183,6 +183,40 @@ describe IO do
       io.gets(chomp: false).should be_nil
     end
 
+    it "does gets with empty string (no peek)" do
+      io = SimpleIOMemory.new("")
+      io.gets(chomp: true).should be_nil
+    end
+
+    it "does gets with empty string (with peek)" do
+      io = IO::Memory.new("")
+      io.gets(chomp: true).should be_nil
+    end
+
+    it "does gets with \\n (no peek)" do
+      io = SimpleIOMemory.new("\n")
+      io.gets(chomp: true).should eq("")
+      io.gets(chomp: true).should be_nil
+    end
+
+    it "does gets with \\n (with peek)" do
+      io = IO::Memory.new("\n")
+      io.gets(chomp: true).should eq("")
+      io.gets(chomp: true).should be_nil
+    end
+
+    it "does gets with \\r\\n (no peek)" do
+      io = SimpleIOMemory.new("\r\n")
+      io.gets(chomp: true).should eq("")
+      io.gets(chomp: true).should be_nil
+    end
+
+    it "does gets with \\r\\n (with peek)" do
+      io = IO::Memory.new("\r\n")
+      io.gets(chomp: true).should eq("")
+      io.gets(chomp: true).should be_nil
+    end
+
     it "does gets with big line" do
       big_line = "a" * 20_000
       io = SimpleIOMemory.new("#{big_line}\nworld\n")

src/io.cr

@@ -752,11 +752,12 @@ abstract class IO
 
   private def gets_slow(delimiter : Char, limit, chomp)
     buffer = String::Builder.new
-    gets_slow(delimiter, limit, chomp, buffer)
-    buffer.empty? ? nil : buffer.to_s
+    bytes_read = gets_slow(delimiter, limit, chomp, buffer)
+    buffer.to_s if bytes_read
   end
 
-  private def gets_slow(delimiter : Char, limit, chomp, buffer : String::Builder) : Nil
+  private def gets_slow(delimiter : Char, limit, chomp, buffer : String::Builder) : Bool
+    bytes_read = false
     chomp_rn = delimiter == '\n' && chomp
 
     while true
@@ -766,6 +767,7 @@ abstract class IO
       end
 
       char, char_bytesize = info
+      bytes_read = true
 
       # Consider the case of \r\n when the delimiter is \n and chomp = true
       if chomp_rn && char == '\r'
@@ -801,6 +803,8 @@ abstract class IO
       break if char_bytesize >= limit
       limit -= char_bytesize
     end
+
+    bytes_read
   end
 
   # Reads until *delimiter* is found or the end of the `IO` is reached.