function: Add validation for parameter name conflicts and update defaulting logic

function/bool_parameter.go

@@ -60,8 +60,11 @@ type BoolParameter struct {
 
 	// Name is a short usage name for the parameter, such as "data". This name
 	// is used in documentation, such as generating a function signature,
-	// however its usage may be extended in the future. If no name is provided,
-	// this will default to "param".
+	// however its usage may be extended in the future.
+	//
+	// If no name is provided, this will default to "param" with a suffix of the
+	// position the parameter is in the function definition. ("param1", "param2", etc.)
+	// If the parameter is variadic, the default name will be "varparam".
 	//
 	// This must be a valid Terraform identifier, such as starting with an
 	// alphabetical character and followed by alphanumeric or underscore
@@ -91,11 +94,7 @@ func (p BoolParameter) GetMarkdownDescription() string {
 
 // GetName returns the parameter name.
 func (p BoolParameter) GetName() string {
-	if p.Name != "" {
-		return p.Name
-	}
-
-	return DefaultParameterName
+	return p.Name
 }
 
 // GetType returns the parameter data type.

function/bool_parameter_test.go

@@ -182,13 +182,7 @@ func TestBoolParameterGetName(t *testing.T) {
 	}{
 		"unset": {
 			parameter: function.BoolParameter{},
-			expected:  function.DefaultParameterName,
-		},
-		"Name-empty": {
-			parameter: function.BoolParameter{
-				Name: "",
-			},
-			expected: function.DefaultParameterName,
+			expected:  "",
 		},
 		"Name-nonempty": {
 			parameter: function.BoolParameter{

function/definition.go

@@ -85,6 +85,27 @@ func (d Definition) Parameter(ctx context.Context, position int) (Parameter, dia
 	return d.Parameters[position], nil
 }
 
+// ParameterName returns the Parameter name for a given argument position. This will be the return
+// from the `(Parameter).GetName` function or a default value. An error diagnostic is raised if the
+// position is outside the expected arguments.
+func (d Definition) ParameterName(ctx context.Context, position int) (string, diag.Diagnostics) {
+	parameter, diags := d.Parameter(ctx, position)
+	if diags.HasError() {
+		return "", diags
+	}
+
+	definedName := parameter.GetName()
+	if definedName != "" {
+		return definedName, nil
+	}
+
+	if position >= len(d.Parameters) {
+		return DefaultVariadicParameterName, nil
+	}
+
+	return fmt.Sprintf("%s%d", DefaultParameterNamePrefix, position+1), nil
+}
+
 // ValidateImplementation contains logic for validating the provider-defined
 // implementation of the definition to prevent unexpected errors or panics. This
 // logic runs during the GetProviderSchema RPC, or via provider-defined unit
@@ -108,6 +129,42 @@ func (d Definition) ValidateImplementation(ctx context.Context) diag.Diagnostics
 		)
 	}
 
+	paramNames := make(map[string]int, len(d.Parameters))
+	for pos := range d.Parameters {
+		// TODO: what should we do with the diags? This should never happen
+		name, _ := d.ParameterName(ctx, pos)
+
+		conflictPos, exists := paramNames[name]
+		if exists {
+			diags.AddError(
+				"Invalid Function Definition",
+				"When validating the function definition, an implementation issue was found. "+
+					"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+					"Parameter names must be unique. "+
+					fmt.Sprintf("Parameters at position %d and %d have the same name %q", conflictPos, pos, name),
+			)
+			continue
+		}
+
+		paramNames[name] = pos
+	}
+
+	if d.VariadicParameter != nil {
+		// TODO: what should we do with the diags? This should never happen
+		name, _ := d.ParameterName(ctx, len(d.Parameters)+1)
+
+		conflictPos, exists := paramNames[name]
+		if exists {
+			diags.AddError(
+				"Invalid Function Definition",
+				"When validating the function definition, an implementation issue was found. "+
+					"This is always an issue with the provider and should be reported to the provider developers.\n\n"+
+					"Parameter names must be unique. "+
+					fmt.Sprintf("Parameter at position %d and the variadic parameter have the same name %q", conflictPos, name),
+			)
+		}
+	}
+
 	return diags
 }