add ExprSyntaxError

hclsyntax/expression.go

@@ -2013,3 +2013,27 @@ func (e *AnonSymbolExpr) Range() hcl.Range {
 func (e *AnonSymbolExpr) StartRange() hcl.Range {
 	return e.SrcRange
 }
+
+// ExprSyntaxError is a placeholder for an invalid expression that could not
+// be parsed due to syntax errors.
+type ExprSyntaxError struct {
+	Placeholder cty.Value
+	ParseDiags  hcl.Diagnostics
+	SrcRange    hcl.Range
+}
+
+func (e *ExprSyntaxError) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
+	return e.Placeholder, e.ParseDiags
+}
+
+func (e *ExprSyntaxError) walkChildNodes(w internalWalkFunc) {
+	// ExprSyntaxError is a leaf node in the tree
+}
+
+func (e *ExprSyntaxError) Range() hcl.Range {
+	return e.SrcRange
+}
+
+func (e *ExprSyntaxError) StartRange() hcl.Range {
+	return e.SrcRange
+}

hclsyntax/expression_template_test.go

@@ -438,6 +438,28 @@ trim`,
 
 }
 
+func TestTemplateExprGracefulValue(t *testing.T) {
+	// we don't care about diags since we know it's invalid config
+	expr, _ := ParseTemplate([]byte(`prefix${provider::}`), "", hcl.Pos{Line: 1, Column: 1, Byte: 0})
+
+	got, _ := expr.Value(nil) // this should not panic
+
+	if !got.RawEquals(cty.UnknownVal(cty.String).RefineNotNull()) {
+		t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, cty.UnknownVal(cty.String).RefineNotNull())
+	}
+}
+
+func TestTemplateExprWrappedGracefulValue(t *testing.T) {
+	// we don't care about diags since we know it's invalid config
+	expr, _ := ParseTemplate([]byte(`${provider::}`), "", hcl.Pos{Line: 1, Column: 1, Byte: 0})
+
+	got, _ := expr.Value(nil) // this should not panic
+
+	if !got.RawEquals(cty.DynamicVal) {
+		t.Errorf("wrong result\ngot:  %#v\nwant: %#v", got, cty.DynamicVal)
+	}
+}
+
 func TestTemplateExprIsStringLiteral(t *testing.T) {
 	tests := map[string]bool{
 		// A simple string value is a string literal

hclsyntax/expression_test.go

@@ -379,8 +379,8 @@ upper(
 					"double::::upper": stdlib.UpperFunc,
 				},
 			},
-			cty.NilVal,
-			1,
+			cty.DynamicVal,
+			2,
 		},
 		{
 			`missing::("foo")`, // missing name after ::
@@ -389,8 +389,8 @@ upper(
 					"missing::": stdlib.UpperFunc,
 				},
 			},
-			cty.NilVal,
-			1,
+			cty.DynamicVal,
+			2,
 		},
 		{
 			`misbehave()`,

hclsyntax/expression_vars.go

@@ -3,7 +3,7 @@
 
 package hclsyntax
 
-// Generated by expression_vars_get.go. DO NOT EDIT.
+// Generated by expression_vars_gen.go. DO NOT EDIT.
 // Run 'go generate' on this package to update the set of functions here.
 
 import (
@@ -22,6 +22,10 @@ func (e *ConditionalExpr) Variables() []hcl.Traversal {
 	return Variables(e)
 }
 
+func (e *ExprSyntaxError) Variables() []hcl.Traversal {
+	return Variables(e)
+}
+
 func (e *ForExpr) Variables() []hcl.Traversal {
 	return Variables(e)
 }

hclsyntax/expression_vars_gen.go

@@ -92,7 +92,7 @@ const outputPreamble = `// Copyright (c) HashiCorp, Inc.
 
 package hclsyntax
 
-// Generated by expression_vars_get.go. DO NOT EDIT.
+// Generated by expression_vars_gen.go. DO NOT EDIT.
 // Run 'go generate' on this package to update the set of functions here.
 
 import (

hclsyntax/parser.go

@@ -1161,15 +1161,20 @@ func (p *parser) finishParsingFunctionCall(name Token) (Expression, hcl.Diagnost
 	for openTok.Type == TokenDoubleColon {
 		nextName := p.Read()
 		if nextName.Type != TokenIdent {
-			diags = append(diags, &hcl.Diagnostic{
+			diag := hcl.Diagnostic{
 				Severity: hcl.DiagError,
 				Summary:  "Missing function name",
 				Detail:   "Function scope resolution symbol :: must be followed by a function name in this scope.",
 				Subject:  &nextName.Range,
 				Context:  hcl.RangeBetween(name.Range, nextName.Range).Ptr(),
-			})
+			}
+			diags = append(diags, &diag)
 			p.recoverOver(TokenOParen)
-			return nil, diags
+			return &ExprSyntaxError{
+				ParseDiags:  hcl.Diagnostics{&diag},
+				Placeholder: cty.DynamicVal,
+				SrcRange:    hcl.RangeBetween(name.Range, nextName.Range),
+			}, diags
 		}
 
 		// Initial versions of HCLv2 didn't support function namespaces, and
@@ -1192,15 +1197,21 @@ func (p *parser) finishParsingFunctionCall(name Token) (Expression, hcl.Diagnost
 	}
 
 	if openTok.Type != TokenOParen {
-		diags = append(diags, &hcl.Diagnostic{
+		diag := hcl.Diagnostic{
 			Severity: hcl.DiagError,
 			Summary:  "Missing open parenthesis",
 			Detail:   "Function selector must be followed by an open parenthesis to begin the function call.",
 			Subject:  &openTok.Range,
 			Context:  hcl.RangeBetween(name.Range, openTok.Range).Ptr(),
-		})
+		}
+
+		diags = append(diags, &diag)
 		p.recoverOver(TokenOParen)
-		return nil, diags
+		return &ExprSyntaxError{
+			ParseDiags:  hcl.Diagnostics{&diag},
+			Placeholder: cty.DynamicVal,
+			SrcRange:    hcl.RangeBetween(name.Range, openTok.Range),
+		}, diags
 	}
 
 	var args []Expression

hclsyntax/parser_test.go

@@ -2559,6 +2559,120 @@ block "valid" {}
 				},
 			},
 		},
+		{
+			"a = partial::namespaced\n",
+			1,
+			&Body{
+				Attributes: Attributes{
+					"a": {
+						Name: "a",
+						Expr: &ExprSyntaxError{
+							Placeholder: cty.DynamicVal,
+							ParseDiags: hcl.Diagnostics{
+								{
+									Severity: hcl.DiagError,
+									Summary:  "Missing open parenthesis",
+									Detail:   "Function selector must be followed by an open parenthesis to begin the function call.",
+									Subject: &hcl.Range{
+										Start: hcl.Pos{Line: 1, Column: 24, Byte: 23},
+										End:   hcl.Pos{Line: 2, Column: 1, Byte: 24},
+									},
+									Context: &hcl.Range{
+										Start: hcl.Pos{Line: 1, Column: 5, Byte: 4},
+										End:   hcl.Pos{Line: 2, Column: 1, Byte: 24},
+									},
+								},
+							},
+							SrcRange: hcl.Range{
+								Start: hcl.Pos{Line: 1, Column: 5, Byte: 4},
+								End:   hcl.Pos{Line: 2, Column: 1, Byte: 24},
+							},
+						},
+						SrcRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 1, Byte: 0},
+							End:      hcl.Pos{Line: 2, Column: 1, Byte: 24},
+						},
+						NameRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 1, Byte: 0},
+							End:      hcl.Pos{Line: 1, Column: 2, Byte: 1},
+						},
+						EqualsRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 3, Byte: 2},
+							End:      hcl.Pos{Line: 1, Column: 4, Byte: 3},
+						},
+					},
+				},
+				Blocks: Blocks{},
+				SrcRange: hcl.Range{
+					Start: hcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   hcl.Pos{Line: 2, Column: 1, Byte: 24},
+				},
+				EndRange: hcl.Range{
+					Start: hcl.Pos{Line: 2, Column: 1, Byte: 24},
+					End:   hcl.Pos{Line: 2, Column: 1, Byte: 24},
+				},
+			},
+		},
+		{
+			"a = partial::\n",
+			1,
+			&Body{
+				Attributes: Attributes{
+					"a": {
+						Name: "a",
+						Expr: &ExprSyntaxError{
+							Placeholder: cty.DynamicVal,
+							ParseDiags: hcl.Diagnostics{
+								{
+									Severity: hcl.DiagError,
+									Summary:  "Missing function name",
+									Detail:   "Function scope resolution symbol :: must be followed by a function name in this scope.",
+									Subject: &hcl.Range{
+										Start: hcl.Pos{Line: 1, Column: 14, Byte: 13},
+										End:   hcl.Pos{Line: 2, Column: 1, Byte: 14},
+									},
+									Context: &hcl.Range{
+										Start: hcl.Pos{Line: 1, Column: 5, Byte: 4},
+										End:   hcl.Pos{Line: 2, Column: 1, Byte: 14},
+									},
+								},
+							},
+							SrcRange: hcl.Range{
+								Start: hcl.Pos{Line: 1, Column: 5, Byte: 4},
+								End:   hcl.Pos{Line: 2, Column: 1, Byte: 14},
+							},
+						},
+						SrcRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 1, Byte: 0},
+							End:      hcl.Pos{Line: 2, Column: 1, Byte: 14},
+						},
+						NameRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 1, Byte: 0},
+							End:      hcl.Pos{Line: 1, Column: 2, Byte: 1},
+						},
+						EqualsRange: hcl.Range{
+							Filename: "",
+							Start:    hcl.Pos{Line: 1, Column: 3, Byte: 2},
+							End:      hcl.Pos{Line: 1, Column: 4, Byte: 3},
+						},
+					},
+				},
+				Blocks: Blocks{},
+				SrcRange: hcl.Range{
+					Start: hcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:   hcl.Pos{Line: 2, Column: 1, Byte: 14},
+				},
+				EndRange: hcl.Range{
+					Start: hcl.Pos{Line: 2, Column: 1, Byte: 14},
+					End:   hcl.Pos{Line: 2, Column: 1, Byte: 14},
+				},
+			},
+		},
 	}
 
 	for _, test := range tests {