feat(controller): Allow whitespace in variable substitution. Fixes #4286

 (#4310)

docs/variables.md

@@ -1,5 +1,33 @@
 # Workflow Variables
 
+Some fields in a workflow specification allow for variable references which are automatically substituted by Argo.
+
+??? note "How to use variables"
+    Variables are enclosed in curly braces and **may** include whitespace between the brackets and variable.
+
+    ``` yaml
+    apiVersion: argoproj.io/v1alpha1
+    kind: Workflow
+    metadata:
+      generateName: hello-world-parameters-
+    spec:
+      entrypoint: whalesay
+      arguments:
+        parameters:
+        - name: message
+          value: hello world
+      templates:
+      - name: whalesay
+        inputs:
+          parameters:
+          - name: message
+        container:
+          image: docker/whalesay
+          command: [cowsay]
+        # args: ["{{ inputs.parameters.message }}"]       <- good
+          args: ["{{inputs.parameters.message}}"]         #  good
+    ```
+
 The following variables are made available to reference various metadata of a workflow:
 
 ## All Templates

workflow/common/util.go

@@ -372,7 +372,7 @@ func SubstituteParams(tmpl *wfv1.Template, globalParams, localParams Parameters)
 func Replace(fstTmpl *fasttemplate.Template, replaceMap map[string]string, allowUnresolved bool) (string, error) {
 	var unresolvedErr error
 	replacedTmpl := fstTmpl.ExecuteFuncString(func(w io.Writer, tag string) (int, error) {
-		replacement, ok := replaceMap[tag]
+		replacement, ok := replaceMap[strings.TrimSpace(tag)]
 		if !ok {
 			// Attempt to resolve nested tags, if possible
 			if index := strings.LastIndex(tag, "{{"); index > 0 {

workflow/common/util_test.go

@@ -157,3 +157,17 @@ func TestNestedReplaceString(t *testing.T) {
 		}
 	}
 }
+
+func TestReplaceStringWithWhiteSpace(t *testing.T) {
+
+	replaceMap := map[string]string{"inputs.parameters.message": "hello world"}
+
+	test := `{{ inputs.parameters.message }}`
+	fstTmpl, err := fasttemplate.NewTemplate(test, "{{", "}}")
+	if assert.NoError(t, err) {
+		replacement, err := Replace(fstTmpl, replaceMap, true)
+		if assert.NoError(t, err) {
+			assert.Equal(t, "hello world", replacement)
+		}
+	}
+}