backport of commit 8c134ba900

hcl2template/parser.go

@@ -190,6 +190,8 @@ func (p *Parser) Parse(filename string, varFiles []string, argVars map[string]st
 			diags = append(diags, morediags...)
 			cfg.LocalBlocks = append(cfg.LocalBlocks, moreLocals...)
 		}
+
+		diags = diags.Extend(cfg.checkForDuplicateLocalDefinition())
 	}
 
 	// parse var files
@@ -296,7 +298,6 @@ func filterVarsFromLogs(inputOrLocal Variables) {
 func (cfg *PackerConfig) Initialize(opts packer.InitializeOptions) hcl.Diagnostics {
 	diags := cfg.InputVariables.ValidateValues()
 	diags = append(diags, cfg.evaluateDatasources(opts.SkipDatasourcesExecution)...)
-	diags = append(diags, checkForDuplicateLocalDefinition(cfg.LocalBlocks)...)
 	diags = append(diags, cfg.evaluateLocalVariables(cfg.LocalBlocks)...)
 
 	filterVarsFromLogs(cfg.InputVariables)

hcl2template/types.packer_config.go

@@ -280,24 +280,29 @@ func (c *PackerConfig) evaluateLocalVariables(locals []*LocalBlock) hcl.Diagnost
 	return diags
 }
 
-func checkForDuplicateLocalDefinition(locals []*LocalBlock) hcl.Diagnostics {
+// checkForDuplicateLocalDefinition walks through the list of defined variables
+// in order to detect duplicate locals definitions.
+func (c *PackerConfig) checkForDuplicateLocalDefinition() hcl.Diagnostics {
 	var diags hcl.Diagnostics
 
-	// we could sort by name and then check contiguous names to use less memory,
-	// but using a map sounds good enough.
-	names := map[string]struct{}{}
-	for _, local := range locals {
-		if _, found := names[local.Name]; found {
-			diags = append(diags, &hcl.Diagnostic{
+	localNames := map[string]*LocalBlock{}
+
+	for _, block := range c.LocalBlocks {
+		loc, ok := localNames[block.Name]
+		if ok {
+			diags = diags.Append(&hcl.Diagnostic{
 				Severity: hcl.DiagError,
 				Summary:  "Duplicate local definition",
-				Detail:   "Duplicate " + local.Name + " definition found.",
-				Subject:  local.Expr.Range().Ptr(),
+				Detail: fmt.Sprintf("Local variable %q is defined twice in your templates. Other definition found at %q",
+					block.Name, loc.Expr.Range()),
+				Subject: block.Expr.Range().Ptr(),
 			})
 			continue
 		}
-		names[local.Name] = struct{}{}
+
+		localNames[block.Name] = block
 	}
+
 	return diags
 }
 

packer_test/local_eval_test.go

@@ -1,5 +1,7 @@
 package packer_test
 
+import "fmt"
+
 func (ts *PackerTestSuite) TestEvalLocalsOrder() {
 	ts.SkipNoAcc()
 
@@ -12,3 +14,18 @@ func (ts *PackerTestSuite) TestEvalLocalsOrder() {
 		SetArgs("console", "./templates/locals_no_order.pkr.hcl").
 		Assert(MustSucceed(), Grep("\\[\\]", grepStdout, grepInvert))
 }
+
+func (ts *PackerTestSuite) TestLocalDuplicates() {
+	pluginDir, cleanup := ts.MakePluginDir()
+	defer cleanup()
+
+	for _, cmd := range []string{"console", "validate", "build"} {
+		ts.Run(fmt.Sprintf("duplicate local detection with %s command - expect error", cmd), func() {
+			ts.PackerCommand().UsePluginDir(pluginDir).
+				SetArgs(cmd, "./templates/locals_duplicate.pkr.hcl").
+				Assert(MustFail(),
+					Grep("Duplicate local definition"),
+					Grep("Local variable \"test\" is defined twice"))
+		})
+	}
+}

packer_test/templates/locals_duplicate.pkr.hcl

@@ -0,0 +1,18 @@
+local "test" {
+    expression = "two"
+    sensitive = true
+}
+
+locals {
+    test = local.test
+}
+
+variable "test" {
+    type = string
+    default = "home"
+}
+source "null" "example" {}
+
+build {
+    sources = ["source.null.example"]
+}