(Closes #2721) Add ArrayConstructor to PSyIR

changelog

@@ -1,3 +1,5 @@
+   32) PR #3458 for #2721. Adds ArrayConstructor support into the PSyIR.
+
    31) PR #3442. Extends Call.get_callee() to permit implicit reshaping
    of arguments.
 

src/psyclone/psyir/backend/fortran.py

@@ -35,6 +35,7 @@
 # Modified J. Henrichs, Bureau of Meteorology
 # Modified A. R. Porter, A. B. G. Chalk and N. Nobre, STFC Daresbury Lab
 # Modified J. Remy, Université Grenoble Alpes, Inria
+# Modified M. Naylor, University of Cambridge, UK
 
 '''PSyIR Fortran backend. Implements a visitor that generates Fortran code
 from a PSyIR tree. '''
@@ -49,9 +50,10 @@
 from psyclone.psyir.frontend.fparser2 import (
     Fparser2Reader, TYPE_MAP_FROM_FORTRAN)
 from psyclone.psyir.nodes import (
-    BinaryOperation, Call, Container, CodeBlock, DataNode, IntrinsicCall,
-    Literal, Member, Node, OMPDependClause, OMPReductionClause, Operation,
-    Range, Routine, Schedule, UnaryOperation, UnknownDirective, IfBlock)
+    ArrayConstructor, BinaryOperation, Call, Container, CodeBlock,
+    DataNode, IntrinsicCall, Literal, Member, Node, OMPDependClause,
+    OMPReductionClause, Operation, Range, Routine, Schedule,
+    UnaryOperation, UnknownDirective, IfBlock)
 from psyclone.psyir.symbols import (
     ArgumentInterface, ArrayType, ContainerSymbol, DataSymbol, DataType,
     DataTypeSymbol, GenericInterfaceSymbol, IntrinsicSymbol,
@@ -1439,6 +1441,18 @@ def literal_node(self, node):
 
         return result
 
+    def arrayconstructor_node(self, node: ArrayConstructor) -> str:
+        '''This method is called when an ArrayConstructor instance is
+        found in the PSyIR tree.
+
+        :param node: an ArrayConstructor PSyIR node.
+
+        :returns: the Fortran code as a string.
+
+        '''
+        contents = ", ".join([self._visit(child) for child in node.children])
+        return "[" + contents + "]"
+
     def ifblock_node(self, node):
         '''This method is called when an IfBlock instance is found in the
         PSyIR tree.

src/psyclone/psyir/frontend/fparser2.py

@@ -34,6 +34,7 @@
 #          J. Henrichs, Bureau of Meteorology
 #          I. Kavcic, Met Office
 # Modified: A. B. G. Chalk, STFC Daresbury Lab
+#           M. Naylor, University of Cambridge, UK
 # -----------------------------------------------------------------------------
 
 ''' This module provides the fparser2 to PSyIR front-end, it follows a
@@ -60,6 +61,7 @@
 from psyclone.errors import InternalError, GenerationError
 from psyclone.psyir.commentable_mixin import CommentableMixin
 from psyclone.psyir.nodes import (
+    ArrayConstructor,
     ArrayMember, ACCRoutineDirective, ArrayOfStructuresReference,
     ArrayReference, Assignment, BinaryOperation, Call, CodeBlock, Container,
     DataNode, Directive, FileContainer, IfBlock, IntrinsicCall, Literal, Loop,
@@ -991,6 +993,7 @@ def __init__(
             Fortran2003.Allocate_Stmt: self._allocate_handler,
             Fortran2003.Allocate_Shape_Spec: self._allocate_shape_spec_handler,
             Fortran2003.Assignment_Stmt: self._assignment_handler,
+            Fortran2003.Array_Constructor: self._array_constructor_handler,
             Fortran2003.Structure_Constructor: self._call_handler,
             Fortran2003.Data_Pointer_Object: self._structure_accessor_handler,
             Fortran2003.Data_Ref: self._structure_accessor_handler,
@@ -4975,6 +4978,43 @@ def _assignment_handler(self, node, parent):
 
         return assignment
 
+    def _array_constructor_handler(
+             self,
+             node: Fortran2003.Array_Constructor,
+             parent: Node) -> ArrayConstructor:
+        '''
+        Transforms an fparser2 Array_Constructor to the PSyIR representation.
+
+        :param node: array constructor node in fparser2 AST.
+        :param parent: parent node of the PSyIR node we are constructing.
+
+        :returns: PSyIR representation of array constructor.
+
+        :raises NotImplementedError: if the parse tree contains unsupported
+            elements.
+        '''
+        ac_spec = node.items[1]
+        if isinstance(ac_spec, Fortran2003.Ac_Value_List):
+            elems = node.items[1].items
+            # Check that no elements are 'Ac_Implied_Do'
+            for elem in elems:
+                if isinstance(elem, Fortran2003.Ac_Implied_Do):
+                    raise NotImplementedError(
+                        "Array constructors with implied do loops cannot be "
+                        "handled in the PSyIR")
+            array_cons = ArrayConstructor(ast=node, parent=parent)
+            self.process_nodes(parent=array_cons, nodes=elems)
+            return array_cons
+        elif isinstance(ac_spec, Fortran2003.Ac_Spec):
+            raise NotImplementedError(
+                "Array constructors with type specifications cannot be "
+                "handled in the PSyIR")
+        else:  # pragma: no cover
+            # This should never be reached, but we defensively raise
+            # an exception just in case.
+            raise NotImplementedError(
+                "Unexpected array constructor form encountered")
+
     def _structure_accessor_handler(self, node, parent):
         '''
         Create the PSyIR for structure accessors found in fparser2 Data_Ref,

src/psyclone/psyir/nodes/__init__.py

@@ -39,6 +39,7 @@
 
 ''' PSyIR nodes package module '''
 
+from psyclone.psyir.nodes.array_constructor import ArrayConstructor
 from psyclone.psyir.nodes.acc_clauses import (
     ACCAsyncQueueClause, ACCCopyClause, ACCCopyInClause,
     ACCCopyOutClause)
@@ -113,6 +114,7 @@
 # this package e.g. 'from psyclone.psyir.nodes import Literal'
 __all__ = [
         'colored',
+        'ArrayConstructor',
         'ArrayMember',
         'ArrayReference',
         'ArrayOfStructuresMember',

src/psyclone/psyir/nodes/array_constructor.py

@@ -0,0 +1,128 @@
+# -----------------------------------------------------------------------------
+# BSD 3-Clause License
+#
+# Copyright (c) 2026, Science and Technology Facilities Council.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice, this
+#   list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright notice,
+#   this list of conditions and the following disclaimer in the documentation
+#   and/or other materials provided with the distribution.
+#
+# * Neither the name of the copyright holder nor the names of its
+#   contributors may be used to endorse or promote products derived from
+#   this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+# -----------------------------------------------------------------------------
+# Authors M. Naylor, University of Cambridge, UK
+# -----------------------------------------------------------------------------
+
+''' This module contains the ArrayConstructor node implementation.'''
+
+from __future__ import annotations
+from typing import Union, TYPE_CHECKING
+from psyclone.psyir.symbols import (
+    UnresolvedType, DataType, ScalarType, ArrayType, DataTypeSymbol)
+from psyclone.psyir.nodes.datanode import DataNode
+if TYPE_CHECKING:
+    from psyclone.psyir.nodes import Node
+
+
+class ArrayConstructor(DataNode):
+    '''
+    Node representing an array constructor.
+    '''
+
+    # Textual description of the node.
+    _children_valid_format = "[DataNode]*"
+    _text_name = "ArrayConstructor"
+    _colour = "yellow"
+
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+
+    @staticmethod
+    def create(elems: list[DataNode]) -> ArrayConstructor:
+        '''Create an ArrayConstructor instance representing an array
+        with the given elements.
+
+        :param elems: the elements of the array being constructed.
+        :returns: an ArrayConstructor instance.
+
+        :raises GenerationError: if the arguments are not of the \
+            expected type.
+        '''
+        array_cons = ArrayConstructor()
+        for elem in elems:
+            array_cons.children.append(elem)
+        return array_cons
+
+    @staticmethod
+    def _validate_child(position: int, child: Node) -> bool:
+        '''
+        :param position: the position to be validated.
+        :param child: a child to be validated.
+
+        :return: whether the given child and position are valid for this node.
+        '''
+        return isinstance(child, DataNode)
+
+    @property
+    def datatype(self) -> Union[DataType, DataTypeSymbol]:
+        '''
+        :returns: the type of this array constructor.
+        '''
+        # The result of an array constructor is always a rank-1 array.
+        # We look through the children to find the array-element type.
+        elem_type = UnresolvedType()
+        for child in self.children:
+            if isinstance(child.datatype, ArrayType):
+                elem_type = child.datatype.elemental_type
+                break
+            elif isinstance(child.datatype, ScalarType):
+                elem_type = child.datatype
+                break
+            elif isinstance(child.datatype, DataTypeSymbol):
+                elem_type = child.datatype
+                break
+
+        # In general, the array size of an array constructor is not known
+        # statically, either due to use of implied do (which is not
+        # yet supported in PSyIR), or due to a Reference to an array
+        # whose size is not known statically, or due to a function/intrinsic
+        # call. It would be possible to chase down these nodes to determine
+        # a more precise size but it's not clear if it's worth the added
+        # complexity. So for now, we uniformly return a runtime-known size.
+        return ArrayType(elem_type, [ArrayType.Extent.ATTRIBUTE])
+
+    def node_str(self, colour: bool = True) -> str:
+        '''
+        Construct a text representation of this node, optionally containing
+        colour control codes.
+
+        :param colour: whether or not to include colour control codes.
+
+        :returns: description of this PSyIR node.
+        '''
+        return f"{self.coloured_name(colour)}[]"
+
+
+# For AutoAPI documentation generation
+__all__ = ['ArrayConstructor']

src/psyclone/psyir/symbols/datasymbol.py

@@ -218,7 +218,7 @@ def initial_value(self, new_value):
         # pylint: disable=import-outside-toplevel
         from psyclone.psyir.nodes import (
             Assignment, Node, Literal, Operation, Reference,
-            CodeBlock, IntrinsicCall)
+            CodeBlock, IntrinsicCall, ArrayConstructor)
         from psyclone.psyir.symbols.datatypes import (ScalarType, ArrayType,
                                                       UnsupportedType)
 
@@ -239,7 +239,8 @@ def initial_value(self, new_value):
             if isinstance(new_value, Node):
                 for node in new_value.walk(Node):
                     if not isinstance(node, (Literal, Operation, Reference,
-                                             CodeBlock, IntrinsicCall)):
+                                             CodeBlock, IntrinsicCall,
+                                             ArrayConstructor)):
                         raise ValueError(
                             f"Error setting initial value for symbol "
                             f"'{self.name}'. PSyIR static expressions can only"

src/psyclone/psyir/transformations/arrayassignment2loops_trans.py

@@ -47,7 +47,7 @@
 from psyclone.psyGen import Transformation
 from psyclone.psyir.nodes import (
     Assignment, Call, IntrinsicCall, Loop, Literal, Node, Range, Reference,
-    CodeBlock, Routine, BinaryOperation)
+    CodeBlock, Routine, BinaryOperation, ArrayConstructor)
 from psyclone.psyir.nodes.array_mixin import ArrayMixin
 from psyclone.psyir.nodes.structure_accessor_mixin import (
     StructureAccessorMixin)
@@ -245,6 +245,17 @@ def validate(
             raise TransformationError(LazyString(
                 lambda: f"{message}, but found:\n{node.debug_string()}"))
 
+        # Do not allow to transform expressions with ArrayConstructors
+        # This could be relaxed in future
+        if node.has_descendant(ArrayConstructor):
+            message = (f"{self.name} does not support array assignments that"
+                       " contain an ArrayConstructor anywhere in"
+                       " the expression")
+            if verbose:
+                node.append_preceding_comment(message)
+            raise TransformationError(LazyString(
+                lambda: f"{message}, but found:\n{node.debug_string()}"))
+
         try:
             node.scope
         except SymbolError:

src/psyclone/tests/core/symbolic_maths_test.py

@@ -251,7 +251,7 @@ def test_symbolic_maths_never_equal_error(fortran_reader):
     source = (
         "program test_prog\n"
         "  integer :: a(2)\n"
-        "  a(:) = (/1, 2/)\n"
+        "  a(:) = (/integer :: 1, 2/)\n"
         "end program test_prog\n")
     psyir = fortran_reader.psyir_from_source(source)
     assignment = psyir.children[0][0]

src/psyclone/tests/psyir/backend/fortran_gen_decls_test.py

@@ -164,7 +164,7 @@ def test_gen_param_decls_case_insensitive(fortran_reader,
         "integer(kind=an_int), parameter :: a_second_int = 5_i_def\n"
         "integer, parameter :: nfieldnames3d = 4\n"
         "integer, dimension(nfieldnames3d), parameter :: "
-        "interpolationlevels = [2, 0, HUGE(InterpolationLevels) / 3, 0]\n")
+        "InterpolationLevels = [2, 0, HUGE(InterpolationLevels) / 3, 0]\n")
 
 
 def test_gen_decls(fortran_writer):

src/psyclone/tests/psyir/backend/fortran_test.py

@@ -54,7 +54,8 @@
     ArrayReference, ArrayOfStructuresReference, Range, StructureReference,
     Schedule, Routine, Return, FileContainer, IfBlock, OMPTaskloopDirective,
     OMPMasterDirective, OMPParallelDirective, Loop, OMPNumTasksClause,
-    OMPDependClause, IntrinsicCall, OMPReductionClause, UnknownDirective)
+    OMPDependClause, IntrinsicCall, OMPReductionClause, UnknownDirective,
+    ArrayConstructor)
 from psyclone.psyir.symbols import (
     ArgumentInterface, ContainerSymbol, DataSymbol, GenericInterfaceSymbol,
     ImportInterface, RoutineSymbol, StaticInterface, Symbol, SymbolTable,
@@ -1742,7 +1743,7 @@ def test_fw_codeblock_2(fortran_reader, fortran_writer, tmpdir):
     '''Check the FortranWriter class codeblock method correctly prints out
     the Fortran representation when there is a code block that is part
     of a line (not a whole line). In this case the data initialisation
-    of the array 'a' "(/ 0.0 /)" is a code block.
+    of the array 'a' "(/ real :: 0.0 /)" is a code block.
 
     '''
     # Generate fparser2 parse tree from Fortran code.
@@ -1751,7 +1752,7 @@ def test_fw_codeblock_2(fortran_reader, fortran_writer, tmpdir):
         "contains\n"
         "subroutine tmp()\n"
         "  real a(1)\n"
-        "  a = (/ 0.0 /)\n"
+        "  a = (/ real :: 0.0 /)\n"
         "end subroutine tmp\n"
         "end module test")
     psyir = fortran_reader.psyir_from_source(code)
@@ -1761,7 +1762,7 @@ def test_fw_codeblock_2(fortran_reader, fortran_writer, tmpdir):
 
     # Generate Fortran from the PSyIR
     result = fortran_writer(psyir)
-    assert "a = (/0.0/)" in result
+    assert "a = (/REAL :: 0.0/)" in result
     assert Compile(tmpdir).string_compiles(result)
 
 
@@ -2351,3 +2352,17 @@ def test_fw_unknowndirective(fortran_writer):
     assert fortran_writer(direc) == "!$omp atomic\n"
     direc = UnknownDirective(" IVDEP", "DIR")
     assert fortran_writer(direc) == "!DIR$ IVDEP\n"
+
+
+def test_array_constructor(fortran_writer):
+    '''
+    Test that the ArrayConstructor visitor generates the expected string.
+    '''
+    array_cons = ArrayConstructor.create([
+                     Literal("1", ScalarType.integer_type()),
+                     Literal("2", ScalarType.integer_type()),
+                     ArrayConstructor.create([
+                         Literal("3", ScalarType.integer_type()),
+                         Literal("4", ScalarType.integer_type())])])
+    output = fortran_writer(array_cons)
+    assert output == "[1, 2, [3, 4]]"