Merge pull request #527 from SteveL-MSFT/expression-index

Add ability to use expression as array index within an expression

Author: SteveL-MSFT

dsc/tests/dsc_expressions.tests.ps1

@@ -10,6 +10,8 @@ Describe 'Expressions tests' {
         @{ text = "[parameters('test').objectArray[0].name]"; expected = 'one' }
         @{ text = "[parameters('test').objectArray[1].value[0]]"; expected = '2' }
         @{ text = "[parameters('test').objectArray[1].value[1].name]"; expected = 'three' }
+        @{ text = "[parameters('test').index]"; expected = '1' }
+        @{ text = "[parameters('test').objectArray[parameters('test').index].name]"; expected = 'two' }
     ) {
         param($text, $expected)
         $yaml = @"
@@ -18,6 +20,7 @@ parameters:
   test:
     type: object
     defaultValue:
+      index: 1
       hello:
         world: there
       array:
@@ -38,9 +41,9 @@ resources:
   properties:
     output: "$text"
 "@
-        $debug = $yaml | dsc -l debug config get -f yaml 2>&1 | Out-String
+        $debug = $yaml | dsc -l trace config get -f yaml 2>&1 | Out-String
         $out = $yaml | dsc config get | ConvertFrom-Json
-        $LASTEXITCODE | Should -Be 0
+        $LASTEXITCODE | Should -Be 0 -Because $debug
         $out.results[0].result.actualState.output | Should -Be $expected -Because $debug
     }
 

dsc_lib/src/parser/expressions.rs

@@ -14,6 +14,7 @@ use crate::parser::functions::Function;
 pub enum Accessor {
     Member(String),
     Index(Value),
+    IndexExpression(Expression),
 }
 
 #[derive(Clone)]
@@ -73,7 +74,8 @@ impl Expression {
                                 Accessor::Index(value)
                             },
                             "expression" => {
-                                return Err(DscError::Parser("Expression index not supported".to_string()));
+                                let expression = Expression::new(statement_bytes, &index_value)?;
+                                Accessor::IndexExpression(expression)
                             },
                             _ => {
                                 return Err(DscError::Parser(format!("Invalid accessor kind: '{accessor_kind}'")));
@@ -118,6 +120,7 @@ impl Expression {
             debug!("Evaluating accessors");
             let mut value = result;
             for accessor in &self.accessors {
+                let mut index = Value::Null;
                 match accessor {
                     Accessor::Member(member) => {
                         if let Some(object) = value.as_object() {
@@ -129,20 +132,31 @@ impl Expression {
                             return Err(DscError::Parser("Member access on non-object value".to_string()));
                         }
                     },
-                    Accessor::Index(index) => {
-                        if let Some(array) = value.as_array() {
-                            let Some(index) = index.as_u64() else {
-                                return Err(DscError::Parser("Index is not a valid number".to_string()));
-                            };
-                            let index = usize::try_from(index)?;
-                            if index >= array.len() {
-                                return Err(DscError::Parser("Index out of bounds".to_string()));
-                            }
-                            value = array[index].clone();
-                        } else {
-                            return Err(DscError::Parser("Index access on non-array value".to_string()));
-                        }
+                    Accessor::Index(index_value) => {
+                        index = index_value.clone();
                     },
+                    Accessor::IndexExpression(expression) => {
+                        index = expression.invoke(function_dispatcher, context)?;
+                        trace!("Expression result: '{:?}'", index);
+                    },
+                }
+
+                if index.is_number() {
+                    if let Some(array) = value.as_array() {
+                        let Some(index) = index.as_u64() else {
+                            return Err(DscError::Parser("Index is not a valid number".to_string()));
+                        };
+                        let index = usize::try_from(index)?;
+                        if index >= array.len() {
+                            return Err(DscError::Parser("Index out of bounds".to_string()));
+                        }
+                        value = array[index].clone();
+                    } else {
+                        return Err(DscError::Parser("Index access on non-array value".to_string()));
+                    }
+                }
+                else if !index.is_null() {
+                    return Err(DscError::Parser("Invalid index type".to_string()));
                 }
             }