From f6bd122f4b1bb8622a0bb6f22ae2c4219402a636 Mon Sep 17 00:00:00 2001
From: Martin Atkins <mart@degeneration.co.uk>
Date: Mon, 15 May 2017 19:37:20 -0700
Subject: [PATCH] json: parsing of keywords

---
 zcl/json/didyoumean.go      | 20 ++++++++++
 zcl/json/didyoumean_test.go | 49 +++++++++++++++++++++++
 zcl/json/parser.go          | 45 ++++++++++++++++++++-
 zcl/json/parser_test.go     | 80 +++++++++++++++++++++++++++++++++++++
 4 files changed, 193 insertions(+), 1 deletion(-)
 create mode 100644 zcl/json/didyoumean.go
 create mode 100644 zcl/json/didyoumean_test.go
 create mode 100644 zcl/json/parser_test.go

diff --git a/zcl/json/didyoumean.go b/zcl/json/didyoumean.go
new file mode 100644
index 0000000..1016026
--- /dev/null
+++ b/zcl/json/didyoumean.go
@@ -0,0 +1,20 @@
+package json
+
+import (
+	"github.com/agext/levenshtein"
+)
+
+var keywords = []string{"false", "true", "null"}
+
+// keywordSuggestion tries to find a valid JSON keyword that is close to the
+// given string and returns it if found. If no keyword is close enough, returns
+// the empty string.
+func keywordSuggestion(given string) string {
+	for _, kw := range keywords {
+		dist := levenshtein.Distance(given, kw, nil)
+		if dist < 3 { // threshold determined experimentally
+			return kw
+		}
+	}
+	return ""
+}
diff --git a/zcl/json/didyoumean_test.go b/zcl/json/didyoumean_test.go
new file mode 100644
index 0000000..999876a
--- /dev/null
+++ b/zcl/json/didyoumean_test.go
@@ -0,0 +1,49 @@
+package json
+
+import "testing"
+
+func TestKeywordSuggestion(t *testing.T) {
+	tests := []struct {
+		Input, Want string
+	}{
+		{"true", "true"},
+		{"false", "false"},
+		{"null", "null"},
+		{"bananas", ""},
+		{"NaN", ""},
+		{"Inf", ""},
+		{"Infinity", ""},
+		{"void", ""},
+		{"undefined", ""},
+
+		{"ture", "true"},
+		{"tru", "true"},
+		{"tre", "true"},
+		{"treu", "true"},
+		{"rtue", "true"},
+
+		{"flase", "false"},
+		{"fales", "false"},
+		{"flse", "false"},
+		{"fasle", "false"},
+		{"fasel", "false"},
+		{"flue", "false"},
+
+		{"nil", "null"},
+		{"nul", "null"},
+		{"unll", "null"},
+		{"nll", "null"},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			got := keywordSuggestion(test.Input)
+			if got != test.Want {
+				t.Errorf(
+					"wrong result\ninput: %q\ngot:   %q\nwant:  %q",
+					test.Input, got, test.Want,
+				)
+			}
+		})
+	}
+}
diff --git a/zcl/json/parser.go b/zcl/json/parser.go
index 4736a7d..5d7a69f 100644
--- a/zcl/json/parser.go
+++ b/zcl/json/parser.go
@@ -1,6 +1,8 @@
 package json
 
 import (
+	"fmt"
+
 	"github.com/apparentlymart/go-zcl/zcl"
 )
 
@@ -180,5 +182,46 @@ func parseString(p *peeker) (node, zcl.Diagnostics) {
 }
 
 func parseKeyword(p *peeker) (node, zcl.Diagnostics) {
-	return nil, nil
+	tok := p.Read()
+	s := string(tok.Bytes)
+
+	switch s {
+	case "true":
+		return &booleanVal{
+			Value:    true,
+			SrcRange: tok.Range,
+		}, nil
+	case "false":
+		return &booleanVal{
+			Value:    false,
+			SrcRange: tok.Range,
+		}, nil
+	case "null":
+		return &nullVal{
+			SrcRange: tok.Range,
+		}, nil
+	case "undefined", "NaN", "Infinity":
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid JSON keyword",
+				Detail:   fmt.Sprintf("The JavaScript identifier %q cannot be used in JSON.", s),
+				Subject:  &tok.Range,
+			},
+		}
+	default:
+		var dym string
+		if suggest := keywordSuggestion(s); suggest != "" {
+			dym = fmt.Sprintf(" Did you mean %q?", suggest)
+		}
+
+		return nil, zcl.Diagnostics{
+			{
+				Severity: zcl.DiagError,
+				Summary:  "Invalid JSON keyword",
+				Detail:   fmt.Sprintf("%q is not a valid JSON keyword.%s", s, dym),
+				Subject:  &tok.Range,
+			},
+		}
+	}
 }
diff --git a/zcl/json/parser_test.go b/zcl/json/parser_test.go
new file mode 100644
index 0000000..44311ee
--- /dev/null
+++ b/zcl/json/parser_test.go
@@ -0,0 +1,80 @@
+package json
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/apparentlymart/go-zcl/zcl"
+	"github.com/davecgh/go-spew/spew"
+)
+
+func TestParse(t *testing.T) {
+	tests := []struct {
+		Input     string
+		Want      node
+		DiagCount int
+	}{
+		{
+			`true`,
+			&booleanVal{
+				Value: true,
+				SrcRange: zcl.Range{
+					Filename: "",
+					Start:    zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:      zcl.Pos{Line: 1, Column: 5, Byte: 4},
+				},
+			},
+			0,
+		},
+		{
+			`false`,
+			&booleanVal{
+				Value: false,
+				SrcRange: zcl.Range{
+					Filename: "",
+					Start:    zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:      zcl.Pos{Line: 1, Column: 6, Byte: 5},
+				},
+			},
+			0,
+		},
+		{
+			`null`,
+			&nullVal{
+				SrcRange: zcl.Range{
+					Filename: "",
+					Start:    zcl.Pos{Line: 1, Column: 1, Byte: 0},
+					End:      zcl.Pos{Line: 1, Column: 5, Byte: 4},
+				},
+			},
+			0,
+		},
+		{
+			`undefined`,
+			nil,
+			1,
+		},
+		{
+			`flase`,
+			nil,
+			1,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Input, func(t *testing.T) {
+			got, diag := parseFileContent([]byte(test.Input), "")
+
+			if len(diag) != test.DiagCount {
+				t.Errorf("got %d diagnostics; want %d\n%s", len(diag), test.DiagCount, spew.Sdump(diag))
+			}
+
+			if !reflect.DeepEqual(got, test.Want) {
+				t.Errorf(
+					"wrong result\ninput: %s\ngot:   %#v\nwant:  %#v",
+					test.Input, got, test.Want,
+				)
+			}
+		})
+	}
+}