Continue parsing module files on error (hashicorp#1172)

* Add test case with invalid symlink in module

* Continue if we encounter an inaccessible file

internal/terraform/parser/module.go

@@ -32,7 +32,9 @@ func ParseModuleFiles(fs FS, modPath string) (ast.ModFiles, ast.ModDiags, error)
 
 		src, err := fs.ReadFile(fullPath)
 		if err != nil {
-			return nil, nil, err
+			// If a file isn't accessible, continue with reading the
+			// remaining module files
+			continue
 		}
 
 		filename := ast.ModFilename(name)

internal/terraform/parser/module_test.go

@@ -83,6 +83,15 @@ func TestParseModuleFiles(t *testing.T) {
 				},
 			},
 		},
+		{
+			"invalid-links",
+			map[string]struct{}{
+				"resources.tf": {},
+			},
+			map[string]hcl.Diagnostics{
+				"resources.tf": nil,
+			},
+		},
 	}
 
 	fs := osFs{}

internal/terraform/parser/testdata/invalid-links/invalid.tf

@@ -0,0 +1 @@
+non-existent-file

internal/terraform/parser/testdata/invalid-links/resources.tf

@@ -0,0 +1,9 @@
+resource "aws_instance" "web" {
+  ami                    = "ami-a0cfeed8"
+  instance_type          = "t2.micro"
+  user_data              = file("init-script.sh")
+
+  tags = {
+    Name = random_pet.name.id
+  }
+}