From 8d100bfde9bafa9b2fa42aaa417e3b91031a851b Mon Sep 17 00:00:00 2001
From: Martin Atkins <mart@degeneration.co.uk>
Date: Wed, 17 Oct 2018 17:47:13 -0700
Subject: [PATCH] tfdiags: Expose expression evaluation information from
 diagnostics

HCL diagnostics relating to expression evaluation include these, so this
is really just to pass that information through our Terraform-specific
diagnostics interface.
---
 tfdiags/diagnostic.go      | 14 ++++++++++++++
 tfdiags/diagnostic_base.go | 10 +++++++---
 tfdiags/error.go           |  5 +++++
 tfdiags/hcl.go             | 10 ++++++++++
 tfdiags/rpc_friendly.go    |  6 ++++++
 tfdiags/simple_warning.go  |  7 ++++++-
 6 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/tfdiags/diagnostic.go b/tfdiags/diagnostic.go
index 2c23f76ae5..c91ba9a529 100644
--- a/tfdiags/diagnostic.go
+++ b/tfdiags/diagnostic.go
@@ -1,9 +1,18 @@
 package tfdiags
 
+import (
+	"github.com/hashicorp/hcl2/hcl"
+)
+
 type Diagnostic interface {
 	Severity() Severity
 	Description() Description
 	Source() Source
+
+	// FromExpr returns the expression-related context for the diagnostic, if
+	// available. Returns nil if the diagnostic is not related to an
+	// expression evaluation.
+	FromExpr() *FromExpr
 }
 
 type Severity rune
@@ -24,3 +33,8 @@ type Source struct {
 	Subject *SourceRange
 	Context *SourceRange
 }
+
+type FromExpr struct {
+	Expression  hcl.Expression
+	EvalContext *hcl.EvalContext
+}
diff --git a/tfdiags/diagnostic_base.go b/tfdiags/diagnostic_base.go
index 6de82ee82f..50bf9d8eba 100644
--- a/tfdiags/diagnostic_base.go
+++ b/tfdiags/diagnostic_base.go
@@ -2,9 +2,9 @@ package tfdiags
 
 // diagnosticBase can be embedded in other diagnostic structs to get
 // default implementations of Severity and Description. This type also
-// has a default implementation of Source that returns no source location
-// information, so embedders should generally override that method to
-// return more useful results.
+// has default implementations of Source and FromExpr that return no source
+// location or expression-related information, so embedders should generally
+// override those method to return more useful results where possible.
 type diagnosticBase struct {
 	severity Severity
 	summary  string
@@ -25,3 +25,7 @@ func (d diagnosticBase) Description() Description {
 func (d diagnosticBase) Source() Source {
 	return Source{}
 }
+
+func (d diagnosticBase) FromExpr() *FromExpr {
+	return nil
+}
diff --git a/tfdiags/error.go b/tfdiags/error.go
index 4ad6b0567d..13f7a714f4 100644
--- a/tfdiags/error.go
+++ b/tfdiags/error.go
@@ -21,3 +21,8 @@ func (e nativeError) Source() Source {
 	// No source information available for a native error
 	return Source{}
 }
+
+func (e nativeError) FromExpr() *FromExpr {
+	// Native errors are not expression-related
+	return nil
+}
diff --git a/tfdiags/hcl.go b/tfdiags/hcl.go
index 24851f4d00..f9aec41c93 100644
--- a/tfdiags/hcl.go
+++ b/tfdiags/hcl.go
@@ -40,6 +40,16 @@ func (d hclDiagnostic) Source() Source {
 	return ret
 }
 
+func (d hclDiagnostic) FromExpr() *FromExpr {
+	if d.diag.Expression == nil || d.diag.EvalContext == nil {
+		return nil
+	}
+	return &FromExpr{
+		Expression:  d.diag.Expression,
+		EvalContext: d.diag.EvalContext,
+	}
+}
+
 // SourceRangeFromHCL constructs a SourceRange from the corresponding range
 // type within the HCL package.
 func SourceRangeFromHCL(hclRange hcl.Range) SourceRange {
diff --git a/tfdiags/rpc_friendly.go b/tfdiags/rpc_friendly.go
index 6cc95cc2ed..485063b0c0 100644
--- a/tfdiags/rpc_friendly.go
+++ b/tfdiags/rpc_friendly.go
@@ -48,6 +48,12 @@ func (d *rpcFriendlyDiag) Source() Source {
 	}
 }
 
+func (d rpcFriendlyDiag) FromExpr() *FromExpr {
+	// RPC-friendly diagnostics cannot preserve expression information because
+	// expressions themselves are not RPC-friendly.
+	return nil
+}
+
 func init() {
 	gob.Register((*rpcFriendlyDiag)(nil))
 }
diff --git a/tfdiags/simple_warning.go b/tfdiags/simple_warning.go
index fb3ac98989..b0f1ecd46c 100644
--- a/tfdiags/simple_warning.go
+++ b/tfdiags/simple_warning.go
@@ -20,6 +20,11 @@ func (e simpleWarning) Description() Description {
 }
 
 func (e simpleWarning) Source() Source {
-	// No source information available for a native error
+	// No source information available for a simple warning
 	return Source{}
 }
+
+func (e simpleWarning) FromExpr() *FromExpr {
+	// Simple warnings are not expression-related
+	return nil
+}