configs: Parser.LoadValuesFile

This method loads a "values file" -- also known as a "tfvars file" -- and
returns the values found inside.

A values file is an HCL file (in either native or JSON syntax) whose
top-level body is treated as a set of arbitrary key/value pairs whose
values may not depend on any variables or functions.

We will load values files through a configs.Parser -- even though values
files are not strictly-speaking part of configuration -- because this
causes them to be registered in our source code cache so that we can
generate source code snippets if we need to report any diagnostics.

configs/parser_values.go

@@ -0,0 +1,43 @@
+package configs
+
+import (
+	"github.com/hashicorp/hcl2/hcl"
+	"github.com/zclconf/go-cty/cty"
+)
+
+// LoadValuesFile reads the file at the given path and parses it as a "values
+// file", which is an HCL config file whose top-level attributes are treated
+// as arbitrary key.value pairs.
+//
+// If the file cannot be read -- for example, if it does not exist -- then
+// a nil map will be returned along with error diagnostics. Callers may wish
+// to disregard the returned diagnostics in this case and instead generate
+// their own error message(s) with additional context.
+//
+// If the returned diagnostics has errors when a non-nil map is returned
+// then the map may be incomplete but should be valid enough for careful
+// static analysis.
+//
+// This method wraps LoadHCLFile, and so it inherits the syntax selection
+// behaviors documented for that method.
+func (p *Parser) LoadValuesFile(path string) (map[string]cty.Value, hcl.Diagnostics) {
+	body, diags := p.LoadHCLFile(path)
+	if body == nil {
+		return nil, diags
+	}
+
+	vals := make(map[string]cty.Value)
+	attrs, attrDiags := body.JustAttributes()
+	diags = append(diags, attrDiags...)
+	if attrs == nil {
+		return vals, diags
+	}
+
+	for name, attr := range attrs {
+		val, valDiags := attr.Expr.Value(nil)
+		diags = append(diags, valDiags...)
+		vals[name] = val
+	}
+
+	return vals, diags
+}

configs/parser_values_test.go

@@ -0,0 +1,113 @@
+package configs
+
+import (
+	"testing"
+
+	"github.com/zclconf/go-cty/cty"
+)
+
+func TestParserLoadValuesFile(t *testing.T) {
+	tests := map[string]struct {
+		Source    string
+		Want      map[string]cty.Value
+		DiagCount int
+	}{
+		"empty.tfvars": {
+			"",
+			map[string]cty.Value{},
+			0,
+		},
+		"empty.json": {
+			"{}",
+			map[string]cty.Value{},
+			0,
+		},
+		"zerolen.json": {
+			"",
+			map[string]cty.Value{},
+			2, // syntax error and missing root object
+		},
+		"one-number.tfvars": {
+			"foo = 1\n",
+			map[string]cty.Value{
+				"foo": cty.NumberIntVal(1),
+			},
+			0,
+		},
+		"one-number.tfvars.json": {
+			`{"foo": 1}`,
+			map[string]cty.Value{
+				"foo": cty.NumberIntVal(1),
+			},
+			0,
+		},
+		"two-bools.tfvars": {
+			"foo = true\nbar = false\n",
+			map[string]cty.Value{
+				"foo": cty.True,
+				"bar": cty.False,
+			},
+			0,
+		},
+		"two-bools.tfvars.json": {
+			`{"foo": true, "bar": false}`,
+			map[string]cty.Value{
+				"foo": cty.True,
+				"bar": cty.False,
+			},
+			0,
+		},
+		"invalid-syntax.tfvars": {
+			"foo bar baz\n",
+			map[string]cty.Value{},
+			1, // attribute or block definition required
+		},
+		"block.tfvars": {
+			"foo = true\ninvalid {\n}\n",
+			map[string]cty.Value{
+				"foo": cty.True,
+			},
+			1, // blocks are not allowed
+		},
+		"variables.tfvars": {
+			"baz = true\nfoo = var.baz\n",
+			map[string]cty.Value{
+				"baz": cty.True,
+				"foo": cty.DynamicVal,
+			},
+			1, // variables cannot be referenced here
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			p := testParser(map[string]string{
+				name: test.Source,
+			})
+			got, diags := p.LoadValuesFile(name)
+			if len(diags) != test.DiagCount {
+				t.Errorf("wrong number of diagnostics %d; want %d", len(diags), test.DiagCount)
+				for _, diag := range diags {
+					t.Logf("- %s", diag)
+				}
+			}
+
+			if len(got) != len(test.Want) {
+				t.Errorf("wrong number of result keys %d; want %d", len(got), len(test.Want))
+			}
+
+			for name, gotVal := range got {
+				wantVal := test.Want[name]
+				if wantVal == cty.NilVal {
+					t.Errorf("unexpected result key %q", name)
+					continue
+				}
+
+				if !gotVal.RawEquals(wantVal) {
+					t.Errorf("wrong value for %q\ngot:  %#v\nwant: %#v", name, gotVal, wantVal)
+					continue
+				}
+			}
+		})
+	}
+}