error if import target is move source (hashicorp#33192)

It is invalid for any import block to have a "to" argument matching any moved block's "from" argument.

internal/configs/module.go

@@ -402,6 +402,11 @@ func (m *Module) appendFile(file *File) hcl.Diagnostics {
 		}
 	}
 
+	// "Moved" blocks just append, because they are all independent of one
+	// another at this level. (We handle any references between them at
+	// runtime.)
+	m.Moved = append(m.Moved, file.Moved...)
+
 	for _, i := range file.Import {
 		for _, mi := range m.Import {
 			if i.To.Equal(mi.To) {
@@ -441,14 +446,25 @@ func (m *Module) appendFile(file *File) hcl.Diagnostics {
 			// will already have been caught.
 		}
 
+		// It is invalid for any import block to have a "to" argument matching
+		// any moved block's "from" argument.
+		for _, mb := range m.Moved {
+			// Comparing string serialisations is good enough here, because we
+			// only care about equality in the case that both addresses are
+			// AbsResourceInstances.
+			if mb.From.String() == i.To.String() {
+				diags = append(diags, &hcl.Diagnostic{
+					Severity: hcl.DiagError,
+					Summary:  "Cannot import to a move source",
+					Detail:   "An import block for ID %q targets resource address %s, but this address appears in the \"from\" argument of a moved block, which is invalid. Please change the import target to a different address, such as the move target.",
+					Subject:  &i.DeclRange,
+				})
+			}
+		}
+
 		m.Import = append(m.Import, i)
 	}
 
-	// "Moved" blocks just append, because they are all independent of one
-	// another at this level. (We handle any references between them at
-	// runtime.)
-	m.Moved = append(m.Moved, file.Moved...)
-
 	return diags
 }
 

internal/configs/testdata/invalid-modules/import-to-moved-from/main.tf

@@ -0,0 +1,12 @@
+import {
+  id = "foo/bar"
+  to = local_file.foo_bar
+}
+
+moved {
+  from = local_file.foo_bar
+  to   = local_file.bar_baz
+}
+
+resource "local_file" "bar_baz" {
+}