Nicer output when an exception bubbles through main

spec/std/callstack_spec.cr

@@ -7,6 +7,12 @@ describe "Backtrace" do
     tempfile.close
     sample = "#{__DIR__}/data/backtrace_sample"
 
+    # CallStack tries to make files relative to the current dir,
+    # so we do the same for tests
+    current_dir = Dir.current
+    current_dir += File::SEPARATOR unless current_dir.ends_with?(File::SEPARATOR)
+    sample = sample.lchop(current_dir)
+
     `bin/crystal build --debug #{sample.inspect} -o #{tempfile.path.inspect}`
     File.exists?(tempfile.path).should be_true
 
@@ -17,9 +23,8 @@ describe "Backtrace" do
     output = `#{tempfile.path}`
 
     # resolved file line:column
-    output.should match(/callee1 at #{sample} 3:10/)
-    output.should match(/callee3 at #{sample} 15:3/)
-    output.should match(/__crystal_main at #{sample} 17:1/)
+    output.should match(/#{sample}:3:10 in 'callee1'/)
+    output.should match(/#{sample}:15:3 in 'callee3'/)
 
     # skipped internal details
     output.should_not match(/src\/callstack\.cr/)

src/callstack.cr

@@ -23,6 +23,14 @@ end
 
 # :nodoc:
 struct CallStack
+  # Compute current directory at the beginning so filenames
+  # are always shown relative to the *starting* working directory.
+  CURRENT_DIR = begin
+    dir = Process::INITIAL_PWD
+    dir += File::SEPARATOR unless dir.ends_with?(File::SEPARATOR)
+    dir
+  end
+
   @@skip = [] of String
 
   def self.skip(filename)
@@ -145,27 +153,63 @@ struct CallStack
   end
 
   private def decode_backtrace
+    show_full_info = ENV["CRYSTAL_CALLSTACK_FULL_INFO"]? == "1"
+
     @callstack.compact_map do |ip|
       pc = CallStack.decode_address(ip)
 
       file, line, column = CallStack.decode_line_number(pc)
-      if file == "??"
-        file_line_column = "??"
-      else
+
+      if file && file != "??"
         next if @@skip.includes?(file)
-        file_line_column = "#{file} #{line}:#{column}"
+
+        # Turn to relative to the current dir, if possible
+        file = file.lchop(CURRENT_DIR)
+
+        file_line_column = "#{file}:#{line}:#{column}"
       end
 
       if name = CallStack.decode_function_name(pc)
         function = name
       elsif frame = CallStack.decode_frame(ip)
         _, sname = frame
         function = String.new(sname)
+
+        # We ignore these because they are part of `raise`'s internals,
+        # and we can't rely on a correct filename being available
+        # (for example if on Mac and without running `dsymutil`)
+        #
+        # We also ignore `main` because it's always at the same place
+        # and adds no info.
+        if function.starts_with?("*raise<") ||
+           function.starts_with?("*CallStack::") ||
+           function.starts_with?("*CallStack#")
+          next
+        end
+
+        # Crystal methods (their mangled name) start with `*`, so
+        # we remove that to have less clutter in the output.
+        function = function.lchop('*')
       else
         function = "???"
       end
 
-      "0x#{ip.address.to_s(16)}: #{function} at #{file_line_column}"
+      if file_line_column
+        if show_full_info && (frame = CallStack.decode_frame(ip))
+          _, sname = frame
+          line = "#{file_line_column} in '#{String.new(sname)}'"
+        else
+          line = "#{file_line_column} in '#{function}'"
+        end
+      else
+        line = function
+      end
+
+      if show_full_info
+        line = "#{line} at 0x#{ip.address.to_s(16)}"
+      end
+
+      line
     end
   end
 

src/exception.cr

@@ -48,6 +48,7 @@ class Exception
   def inspect_with_backtrace(io : IO)
     io << message << " (" << self.class << ")\n"
     backtrace?.try &.each do |frame|
+      io.print "  from "
       io.puts frame
     end
     io.flush