added an optional allow_trailing_comma flag

can be used to disallow extra trailing commas in arrays and objects (it is true by default and thus allowed)
Fixes #569

Author: jacobwilliams

fpm.toml

@@ -261,4 +261,9 @@ main       = "jf_test_49.F90"
 [[test]]
 name       = "jf_test_50"
 source-dir = "src/tests"
-main       = "jf_test_50.F90"
+main       = "jf_test_50.F90"
+
+[[test]]
+name       = "jf_test_51"
+source-dir = "src/tests"
+main       = "jf_test_51.F90"

src/json_initialize_arguments.inc

@@ -111,4 +111,7 @@ logical(LK),intent(in),optional :: strict_integer_type_checking
   !! * If true, an exception will be raised if the integer
   !!   value cannot be read.
   !!
+  !! (default is true)
+logical(LK),intent(in),optional :: allow_trailing_comma
+  !! Allow a single trailing comma in arrays and objects.
   !! (default is true)

src/json_initialize_dummy_arguments.inc

@@ -22,4 +22,5 @@ stop_on_error,&
 null_to_real_mode,&
 non_normal_mode,&
 use_quiet_nan, &
-strict_integer_type_checking &
+strict_integer_type_checking, &
+allow_trailing_comma &

src/json_value_module.F90

@@ -287,6 +287,9 @@ module json_value_module
                             !! * If true [default], an exception will be raised if an integer
                             !!   value cannot be read when parsing JSON.
 
+        logical(LK) :: allow_trailing_comma = .true.
+                            !! Allow a single trailing comma in arrays and objects.
+
         integer :: ichunk = 0 !! index in `chunk` for [[pop_char]]
                               !! when `use_unformatted_stream=True`
         integer :: filesize = 0 !! the file size when when `use_unformatted_stream=True`
@@ -1140,6 +1143,10 @@ subroutine json_initialize(me,&
         me%strict_integer_type_checking = strict_integer_type_checking
     end if
 
+    if (present(allow_trailing_comma)) then
+        me%allow_trailing_comma = allow_trailing_comma
+    end if
+
     !Set the format for real numbers:
     ! [if not changing it, then it remains the same]
 
@@ -10154,7 +10161,7 @@ recursive subroutine parse_value(json, unit, str, value)
 
                 ! start object
                 call json%to_object(value)    !allocate class
-                call json%parse_object(unit, str, value)
+                call json%parse_object(unit, str, value, expecting_next_element=.false.)
 
             case (start_array)
 
@@ -10879,14 +10886,17 @@ end subroutine to_array
 !>
 !  Core parsing routine.
 
-    recursive subroutine parse_object(json, unit, str, parent)
+    recursive subroutine parse_object(json, unit, str, parent, expecting_next_element)
 
     implicit none
 
     class(json_core),intent(inout)      :: json
     integer(IK),intent(in)              :: unit    !! file unit number (if parsing from a file)
     character(kind=CK,len=*),intent(in) :: str     !! JSON string (if parsing from a string)
     type(json_value),pointer            :: parent  !! the parsed object will be added as a child of this
+    logical(LK),intent(in) :: expecting_next_element !! if true, this object is preceeded by a comma, so
+                                                     !! we expect a valid object to exist. used to check
+                                                     !! for trailing delimiters.
 
     type(json_value),pointer :: pair  !! temp variable
     logical(LK)              :: eof   !! end of file flag
@@ -10907,13 +10917,18 @@ recursive subroutine parse_object(json, unit, str, parent)
 
         ! pair name
         call json%pop_char(unit, str=str, eof=eof, skip_ws=.true., &
-                            skip_comments=json%allow_comments, popped=c)
+                           skip_comments=json%allow_comments, popped=c)
         if (eof) then
             call json%throw_exception('Error in parse_object:'//&
                                       ' Unexpected end of file while parsing start of object.')
             return
         else if (end_object == c) then
             ! end of an empty object
+            if (expecting_next_element .and. .not. json%allow_trailing_comma) then
+                ! this is a dangling comma.
+                call json%throw_exception('Error in parse_object: '//&
+                                          'Dangling comma when parsing an object.')
+            end if
             return
         else if (quotation_mark == c) then
             call json_value_create(pair)
@@ -10935,7 +10950,7 @@ recursive subroutine parse_object(json, unit, str, parent)
 
         ! pair value
         call json%pop_char(unit, str=str, eof=eof, skip_ws=.true., &
-                            skip_comments=json%allow_comments, popped=c)
+                           skip_comments=json%allow_comments, popped=c)
         if (eof) then
             call json%destroy(pair)
             call json%throw_exception('Error in parse_object:'//&
@@ -10959,14 +10974,15 @@ recursive subroutine parse_object(json, unit, str, parent)
 
         ! another possible pair
         call json%pop_char(unit, str=str, eof=eof, skip_ws=.true., &
-                            skip_comments=json%allow_comments, popped=c)
+                           skip_comments=json%allow_comments, popped=c)
         if (eof) then
             call json%throw_exception('Error in parse_object: '//&
                                       'End of file encountered when parsing an object')
             return
         else if (delimiter == c) then
             ! read the next member
-            call json%parse_object(unit = unit, str=str, parent = parent)
+            call json%parse_object(unit = unit, str=str, parent = parent, &
+                                   expecting_next_element=.true.)
         else if (end_object == c) then
             ! end of object
             return
@@ -10996,6 +11012,9 @@ recursive subroutine parse_array(json, unit, str, array)
     type(json_value),pointer :: element !! temp variable for array element
     logical(LK)              :: eof     !! end of file flag
     character(kind=CK,len=1) :: c       !! character returned by [[pop_char]]
+    logical(LK) :: expecting_next_element !! to check for trailing delimiters
+
+    expecting_next_element = .false.
 
     do
 
@@ -11011,7 +11030,10 @@ recursive subroutine parse_array(json, unit, str, array)
         end if
 
         ! parse value will deallocate an empty array value
-        if (associated(element)) call json%add(array, element)
+        if (associated(element)) then
+            expecting_next_element = .false.
+            call json%add(array, element)
+        end if
 
         ! popped the next character
         call json%pop_char(unit, str=str, eof=eof, skip_ws=.true., &
@@ -11024,9 +11046,15 @@ recursive subroutine parse_array(json, unit, str, array)
             exit
         else if (delimiter == c) then
             ! parse the next element
+            expecting_next_element = .true.
             cycle
         else if (end_array == c) then
             ! end of array
+            if (expecting_next_element .and. .not. json%allow_trailing_comma) then
+                ! this is a dangling comma.
+                call json%throw_exception('Error in parse_array: '//&
+                                          'Dangling comma when parsing an array.')
+            end if
             exit
         else
             call json%throw_exception('Error in parse_array: '//&

src/tests/jf_test_51.F90

@@ -0,0 +1,92 @@
+!*****************************************************************************************
+!>
+!  Module for the 51th unit test. See Issue #569.
+
+module jf_test_51_mod
+
+    use json_module, wp => json_RK, IK => json_IK, LK => json_LK, CK => json_CK
+    use, intrinsic :: iso_fortran_env , only: error_unit, output_unit
+
+    implicit none
+
+    private
+    public :: test_51
+
+contains
+
+    subroutine test_51(error_cnt)
+
+    !! 51th unit test. see Issue #569
+
+    integer,intent(out) :: error_cnt
+
+    type(json_file) :: json
+
+    error_cnt = 0
+
+    write(error_unit,'(A)') ''
+    write(error_unit,'(A)') '================================='
+    write(error_unit,'(A)') '   EXAMPLE 51'
+    write(error_unit,'(A)') '================================='
+    write(error_unit,'(A)') ''
+
+    ! array cases:
+    call json%initialize(allow_trailing_comma = .false.)
+    call json%deserialize('{"a" : [1,2,3,]}')
+    if (.not. json%failed()) then
+        error_cnt = error_cnt + 1
+        write(error_unit,'(A)') 'read array with trailing comma'
+    else
+        ! it was supposed to fail
+        write(output_unit,'(A)') '1 success'
+    end if
+
+    call json%initialize(allow_trailing_comma = .true.)
+    call json%deserialize('{"a" : [1,2,3,]}')
+    if (json%failed()) then
+        error_cnt = error_cnt + 1
+        write(error_unit,'(A)') 'failed to read array with trailing comma'
+    else
+        write(output_unit,'(A)') '2 success'
+    end if
+
+    ! object cases:
+    call json%initialize(allow_trailing_comma = .false.)
+    call json%deserialize('{"a" : 1, "b" : 2, }')
+    if (.not. json%failed()) then
+        error_cnt = error_cnt + 1
+        write(error_unit,'(A)') 'read object with trailing comma'
+    else
+        ! it was supposed to fail
+        write(output_unit,'(A)') '3 success'
+    end if
+    call json%initialize(allow_trailing_comma = .true.)
+    call json%deserialize('{"a" : 1, "b" : 2, }')
+    if (json%failed()) then
+        error_cnt = error_cnt + 1
+        write(error_unit,'(A)') 'failed to read object with trailing comma'
+    else
+        write(output_unit,'(A)') '4 success'
+    end if
+
+    end subroutine test_51
+
+end module jf_test_51_mod
+!*****************************************************************************************
+
+!*****************************************************************************************
+#ifndef INTEGRATED_TESTS
+program jf_test_51
+
+    use jf_test_51_mod , only: test_51
+
+    implicit none
+    integer :: n_errors
+
+    call test_51(n_errors)
+    if (n_errors /= 0) stop 1
+
+end program jf_test_51
+#endif
+!*****************************************************************************************
+

visual_studio/jsonfortrantest/jsonfortrantest.vfproj

@@ -96,5 +96,6 @@
 		<File RelativePath="..\..\src\tests\jf_test_48.F90"/>
 		<File RelativePath="..\..\src\tests\jf_test_49.F90"/>
 		<File RelativePath="..\..\src\tests\jf_test_50.F90"/>
+		<File RelativePath="..\..\src\tests\jf_test_51.F90"/>
 		<File RelativePath=".\jsonfortrantest.f90"/></Filter></Files>
 	<Globals/></VisualStudioProject>