Update docs to clarify how to use build vars in build template engines (#10141)

website/pages/docs/builders/amazon/chroot.mdx

@@ -557,6 +557,22 @@ Usage example:
 <Tab heading="HCL2">
 
 ```hcl
+// When accessing one of these variables from inside the builder, you need to
+// use the golang templating syntax. This is due to an architectural quirk that
+// won't be easily resolvable until legacy json templates are deprecated:
+
+{
+source "amazon-ebs" "basic-example" {
+  tags = {
+        OS_Version = "Ubuntu"
+        Release = "Latest"
+        Base_AMI_ID = "{{ .SourceAMI }}"
+        Base_AMI_Name = "{{ .SourceAMIName }}"
+    }
+}
+
+// when accessing one of the variables from a provisioner or post-processor, use
+// hcl-syntax
 post-processor "manifest" {
     output = "manifest.json"
     strip_path = true

website/pages/docs/builders/amazon/ebs.mdx

@@ -361,6 +361,22 @@ Usage example:
 <Tab heading="HCL2">
 
 ```hcl
+// When accessing one of these variables from inside the builder, you need to
+// use the golang templating syntax. This is due to an architectural quirk that
+// won't be easily resolvable until legacy json templates are deprecated:
+
+{
+source "amazon-ebs" "basic-example" {
+  tags = {
+        OS_Version = "Ubuntu"
+        Release = "Latest"
+        Base_AMI_ID = "{{ .SourceAMI }}"
+        Base_AMI_Name = "{{ .SourceAMIName }}"
+    }
+}
+
+// when accessing one of the variables from a provisioner or post-processor, use
+// hcl-syntax
 post-processor "manifest" {
     output = "manifest.json"
     strip_path = true

website/pages/docs/builders/amazon/ebssurrogate.mdx

@@ -265,6 +265,22 @@ Usage example:
 <Tab heading="HCL2">
 
 ```hcl
+// When accessing one of these variables from inside the builder, you need to
+// use the golang templating syntax. This is due to an architectural quirk that
+// won't be easily resolvable until legacy json templates are deprecated:
+
+{
+source "amazon-ebs" "basic-example" {
+  tags = {
+        OS_Version = "Ubuntu"
+        Release = "Latest"
+        Base_AMI_ID = "{{ .SourceAMI }}"
+        Base_AMI_Name = "{{ .SourceAMIName }}"
+    }
+}
+
+// when accessing one of the variables from a provisioner or post-processor, use
+// hcl-syntax
 post-processor "manifest" {
     output = "manifest.json"
     strip_path = true

website/pages/docs/builders/amazon/ebsvolume.mdx

@@ -312,6 +312,22 @@ Usage example:
 <Tab heading="HCL2">
 
 ```hcl
+// When accessing one of these variables from inside the builder, you need to
+// use the golang templating syntax. This is due to an architectural quirk that
+// won't be easily resolvable until legacy json templates are deprecated:
+
+{
+source "amazon-ebs" "basic-example" {
+  tags = {
+        OS_Version = "Ubuntu"
+        Release = "Latest"
+        Base_AMI_ID = "{{ .SourceAMI }}"
+        Base_AMI_Name = "{{ .SourceAMIName }}"
+    }
+}
+
+// when accessing one of the variables from a provisioner or post-processor, use
+// hcl-syntax
 post-processor "manifest" {
     output = "manifest.json"
     strip_path = true

website/pages/docs/builders/amazon/instance.mdx

@@ -258,6 +258,22 @@ Usage example:
 <Tab heading="HCL2">
 
 ```hcl
+// When accessing one of these variables from inside the builder, you need to
+// use the golang templating syntax. This is due to an architectural quirk that
+// won't be easily resolvable until legacy json templates are deprecated:
+
+{
+source "amazon-ebs" "basic-example" {
+  tags = {
+        OS_Version = "Ubuntu"
+        Release = "Latest"
+        Base_AMI_ID = "{{ .SourceAMI }}"
+        Base_AMI_Name = "{{ .SourceAMIName }}"
+    }
+}
+
+// when accessing one of the variables from a provisioner or post-processor, use
+// hcl-syntax
 post-processor "manifest" {
     output = "manifest.json"
     strip_path = true