fix(compute): clarify fastly.toml error message when file not found (#1556)

Add "file not found" to the `ErrReadingManifest` error message to make
it clearer that the file doesn't exist, rather than a parsing or
permission error.

  ### Change summary

The current error message "error reading fastly.toml" is somewhat
ambiguous and doesn't clearly indicate whether the file is missing or
has parsing errors. The remediation text was present but it still seems
easy to misinterpret the actual problem (as proven by it managing to
throw both me, Claude and ChatGPT off 😅).

This change adds ": file not found" to the error message to make it even
more apparent that the file doesn't exist.

  **Before:**
ERROR: error reading fastly.toml. Ensure the Fastly CLI is being run
within a directory containing a fastly.toml
  file...

  **After:**
ERROR: error reading fastly.toml: file not found. Ensure the Fastly CLI
is being run within a directory containing
   a fastly.toml file...

  All Submissions:

  * [x] Have you followed the guidelines in our Contributing document?
* [x] Have you checked to ensure there aren't other open [Pull
Requests](https://github.com/fastly/cli/pulls) for
  the same update/change?

  ### Changes to Core Features:

  * [x] Have you written new tests for your core changes, as applicable?
  * [ ] Have you successfully run tests with your changes locally?

  ### User Impact

* Users will now more easily understand that the `fastly.toml` file is
missing.

Author: backkem

CHANGELOG.md

@@ -8,6 +8,7 @@
 - build(dockerfile-rust): add wasm tools to the rust docker container ([#1552](https://github.com/fastly/cli/pull/1552))
 
 ### Bug fixes:
+- fix(compute): clarify fastly.toml error message when file not found ([#1556](https://github.com/fastly/cli/pull/1556))
 
 ### Dependencies:
 - build(deps): `github.com/hashicorp/cap` from 0.10.0 to 0.11.0 ([#1546](https://github.com/fastly/cli/pull/1546))

pkg/commands/compute/build_test.go

@@ -40,7 +40,7 @@ func TestBuildRust(t *testing.T) {
 		{
 			name:                 "no fastly.toml manifest",
 			args:                 args("compute build"),
-			wantError:            "error reading fastly.toml",
+			wantError:            "error reading fastly.toml: file not found",
 			wantRemediationError: "Run `fastly compute init` to ensure a correctly configured manifest.",
 		},
 		{
@@ -300,7 +300,7 @@ func TestBuildGo(t *testing.T) {
 		{
 			name:                 "no fastly.toml manifest",
 			args:                 args("compute build"),
-			wantError:            "error reading fastly.toml",
+			wantError:            "error reading fastly.toml: file not found",
 			wantRemediationError: "Run `fastly compute init` to ensure a correctly configured manifest.",
 		},
 		{
@@ -494,7 +494,7 @@ func TestBuildJavaScript(t *testing.T) {
 		{
 			name:                 "no fastly.toml manifest",
 			args:                 args("compute build"),
-			wantError:            "error reading fastly.toml",
+			wantError:            "error reading fastly.toml: file not found",
 			wantRemediationError: "Run `fastly compute init` to ensure a correctly configured manifest.",
 		},
 		{

pkg/commands/compute/deploy_test.go

@@ -112,7 +112,7 @@ func TestDeploy(t *testing.T) {
 		{
 			name:                 "no fastly.toml manifest",
 			args:                 args("compute deploy --token 123"),
-			wantError:            "error reading fastly.toml",
+			wantError:            "error reading fastly.toml: file not found",
 			wantRemediationError: errors.ComputeInitRemediation,
 			noManifest:           true,
 		},

pkg/errors/errors.go

@@ -75,7 +75,7 @@ var ErrNoID = RemediationError{
 
 // ErrReadingManifest means there was a problem reading the fastly.toml.
 var ErrReadingManifest = RemediationError{
-	Inner:       fmt.Errorf("error reading fastly.toml"),
+	Inner:       fmt.Errorf("error reading fastly.toml: file not found"),
 	Remediation: "Ensure the Fastly CLI is being run within a directory containing a fastly.toml file. " + ComputeInitRemediation,
 }