Unfold the "hcl" directory up into the root

The main HCL package is more visible this way, and so it's easier than
having to pick it out from dozens of other package directories.

1 files changed, 44 insertions, 0 deletions

diff --git a/expr_map.go b/expr_map.go
new file mode 100644
index 0000000..96d1ce4
--- /dev/null
+++ b/expr_map.go
@@ -0,0 +1,44 @@
+package hcl
+
+// ExprMap tests if the given expression is a static map construct and,
+// if so, extracts the expressions that represent the map elements.
+// If the given expression is not a static map, error diagnostics are
+// returned.
+//
+// A particular Expression implementation can support this function by
+// offering a method called ExprMap that takes no arguments and returns
+// []KeyValuePair. This method should return nil if a static map cannot
+// be extracted.  Alternatively, an implementation can support
+// UnwrapExpression to delegate handling of this function to a wrapped
+// Expression object.
+func ExprMap(expr Expression) ([]KeyValuePair, Diagnostics) {
+	type exprMap interface {
+		ExprMap() []KeyValuePair
+	}
+
+	physExpr := UnwrapExpressionUntil(expr, func(expr Expression) bool {
+		_, supported := expr.(exprMap)
+		return supported
+	})
+
+	if exM, supported := physExpr.(exprMap); supported {
+		if pairs := exM.ExprMap(); pairs != nil {
+			return pairs, nil
+		}
+	}
+	return nil, Diagnostics{
+		&Diagnostic{
+			Severity: DiagError,
+			Summary:  "Invalid expression",
+			Detail:   "A static map expression is required.",
+			Subject:  expr.StartRange().Ptr(),
+		},
+	}
+}
+
+// KeyValuePair represents a pair of expressions that serve as a single item
+// within a map or object definition construct.
+type KeyValuePair struct {
+	Key   Expression
+	Value Expression
+}