test: simple unit test for file functions

preview.go

@@ -97,7 +97,9 @@ func Preview(ctx context.Context, input Input, dir fs.FS) (output *Output, diagn
 	// moduleSource is "" for a local module
 	p := parser.New(dir, "",
 		parser.OptionStopOnHCLError(false),
+		// Obviously prevent http downloads.
 		parser.OptionWithDownloads(false),
+		// Cached moules are sourced from a file on the host disk.
 		parser.OptionWithSkipCachedModules(true),
 		parser.OptionWithTFVarsPaths(varFiles...),
 		parser.OptionWithEvalHook(planHook),

preview_test.go

@@ -403,6 +403,16 @@ func Test_Extract(t *testing.T) {
 			unknownTags: []string{},
 			params:      map[string]assertParam{},
 		},
+		{
+			name:        "diskaccess",
+			dir:         "diskaccess",
+			expTags:     map[string]string{},
+			unknownTags: []string{},
+			params: map[string]assertParam{
+				"file": ap().
+					optVals("hello world", types.UnknownStringValue),
+			},
+		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()

testdata/diskaccess/hello.txt

@@ -0,0 +1 @@
+hello world

testdata/diskaccess/main.tf

@@ -0,0 +1,26 @@
+terraform {
+  required_providers {
+    coder = {
+      source = "coder/coder"
+      version = "2.4.0-pre0"
+    }
+  }
+}
+
+
+data "coder_parameter" "file" {
+  name        = "file"
+  description = "Attempt to read some files."
+  type        = "string"
+  order       = 1
+
+  option {
+    name  = "Local"
+    value = file("./hello.txt")
+  }
+
+  option {
+    name  = "Outer"
+    value = file("../README.md")
+  }
+}