From 4147fa779c26bdea044e8d77bd13989beacc81c8 Mon Sep 17 00:00:00 2001
From: Martin Atkins <mart@degeneration.co.uk>
Date: Thu, 11 Oct 2018 17:58:59 -0700
Subject: [PATCH] command: WIP input variable handling

---
 command/meta_vars.go | 97 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 command/meta_vars.go

diff --git a/command/meta_vars.go b/command/meta_vars.go
new file mode 100644
index 0000000000..469f2c4b5c
--- /dev/null
+++ b/command/meta_vars.go
@@ -0,0 +1,97 @@
+package command
+
+import (
+	"strings"
+
+	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/configs"
+	"github.com/hashicorp/terraform/terraform"
+	"github.com/hashicorp/terraform/tfdiags"
+)
+
+// collectVariables inspects the various places that root module input variable
+// values can come from and constructs a map ready to be passed to the
+// backend as part of a backend.Operation.
+//
+// This method does not return an error or diagnostics directly, but one or
+// more of the returned unparsed value objects may produce diagnostics when
+// finally parsed within the backend code.
+func (m *Meta) collectVariables() map[string]backend.UnparsedVariableValue {
+	ret := map[string]backend.UnparsedVariableValue{}
+
+	// First we'll deal with environment variables, since they have the lowest
+	// precedence.
+	{
+		env := os.Environ()
+		for _, raw := range env {
+			if !strings.HasPrefix(raw, terraform.VarEnvPrefix) {
+				continue
+			}
+			raw = raw[len(terraform.VarEnvPrefix):] // trim the prefix
+
+			eq := strings.Index(raw, "=")
+			if eq == -1 {
+				// Seems invalid, so we'll ignore it.
+				continue
+			}
+
+			name := raw[:eq]
+			rawVal := raw[eq+1:]
+
+			ret[name] = unparsedVariableValueString{
+				str:        rawVal,
+				name:       name,
+				sourceType: terraform.ValueFromEnvVar,
+			}
+		}
+	}
+
+	// Next up we have some implicit files that are loaded automatically
+	// if they are present. There's the original terraform.tfvars
+	// (DefaultVarsFilename) along with the later-added search for all files
+	// ending in .auto.tfvars.
+}
+
+// unparsedVariableValueExpression is a backend.UnparsedVariableValue
+// implementation that evaluates an already-parsed HCL expression. This is
+// intended to deal with expressions inside "tfvars" files.
+type unparsedVariableValueExpression struct {
+	expr       hcl.Expression
+	sourceType terraform.ValueSourceType
+}
+
+func (v unparsedVariableValueExpression) ParseVariableValue(mode configs.VariableParsingMode) (*terraform.InputValue, tfdiags.Diagnostics) {
+	var diags tfdiags.Diagnostics
+	val, hclDiags := v.expr.Value(nil) // nil because no function calls or variable references are allowed here
+	diags = diags.Append(hclDiags)
+
+	rng := tfdiags.SourceRangeFromHCL(v.expr.SourceRange())
+
+	return &terraform.InputValue{
+		Value:       val,
+		SourceType:  v.sourceType,
+		SourceRange: rng,
+	}, diags
+}
+
+// unparsedVariableValueString is a backend.UnparsedVariableValue
+// implementation that parses its value from a string. This can be used
+// to deal with values given directly on the command line and via environment
+// variables.
+type unparsedVariableValueString struct {
+	str        string
+	name       string
+	sourceType terraform.ValueSourceType
+}
+
+func (v unparsedVariableValueString) ParseVariableValue(mode configs.VariableParsingMode) (*terraform.InputValue, tfdiags.Diagnostics) {
+	var diags tfdiags.Diagnostics
+
+	val, hclDiags := mode.Parse(v.name, v.str)
+	diags = diags.Append(hclDiags)
+
+	return &terraform.InputValue{
+		Value:       val,
+		SourceType:  v.sourceType,
+	}, diags
+}