Add a custom mechanism for looking up comments.

.github/workflows/test.yaml

@@ -1,5 +1,11 @@
 name: Test Go
-on: [push]
+on:
+  push:
+    tags:
+      - v*
+    branches:
+      - main
+  pull_request:
 jobs:
   test:
     name: Test

fixtures/custom_comments.json

@@ -0,0 +1,114 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://github.com/invopop/jsonschema/examples/user",
+  "$ref": "#/$defs/User",
+  "$defs": {
+    "NamedPets": {
+      "additionalProperties": {
+        "$ref": "#/$defs/Pet"
+      },
+      "type": "object",
+      "description": "NamedPets is a map of animal names to pets."
+    },
+    "Pet": {
+      "properties": {
+        "name": {
+          "type": "string",
+          "title": "Name",
+          "description": "Name of the animal."
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "required": [
+        "name"
+      ],
+      "description": "Pet defines the user's fury friend."
+    },
+    "Pets": {
+      "items": {
+        "$ref": "#/$defs/Pet"
+      },
+      "type": "array",
+      "description": "Pets is a collection of Pet objects."
+    },
+    "Plant": {
+      "properties": {
+        "variant": {
+          "type": "string",
+          "title": "Variant",
+          "description": "This comment will be used"
+        },
+        "multicellular": {
+          "type": "boolean",
+          "title": "Multicellular",
+          "description": "Multicellular is true if the plant is multicellular"
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "required": [
+        "variant"
+      ],
+      "description": "Plant represents the plants the user might have and serves as a test of structs inside a `type` set."
+    },
+    "User": {
+      "properties": {
+        "id": {
+          "type": "integer",
+          "description": "Field ID of Go type github.com/invopop/jsonschema/examples.User."
+        },
+        "name": {
+          "type": "string",
+          "maxLength": 20,
+          "minLength": 1,
+          "pattern": ".*",
+          "title": "the name",
+          "description": "this is a property",
+          "default": "alex",
+          "examples": [
+            "joe",
+            "lucy"
+          ]
+        },
+        "friends": {
+          "items": {
+            "type": "integer"
+          },
+          "type": "array",
+          "description": "list of IDs, omitted when empty"
+        },
+        "tags": {
+          "type": "object",
+          "description": "Field Tags of Go type github.com/invopop/jsonschema/examples.User."
+        },
+        "pets": {
+          "$ref": "#/$defs/Pets",
+          "description": "Field Pets of Go type github.com/invopop/jsonschema/examples.User."
+        },
+        "named_pets": {
+          "$ref": "#/$defs/NamedPets",
+          "description": "Field NamedPets of Go type github.com/invopop/jsonschema/examples.User."
+        },
+        "plants": {
+          "items": {
+            "$ref": "#/$defs/Plant"
+          },
+          "type": "array",
+          "title": "Plants",
+          "description": "Field Plants of Go type github.com/invopop/jsonschema/examples.User."
+        }
+      },
+      "additionalProperties": false,
+      "type": "object",
+      "required": [
+        "id",
+        "name",
+        "pets",
+        "named_pets",
+        "plants"
+      ],
+      "description": "Go type User, defined in package github.com/invopop/jsonschema/examples."
+    }
+  }
+}

reflect.go

@@ -143,6 +143,16 @@ type Reflector struct {
 	// AdditionalFields allows adding structfields for a given type
 	AdditionalFields func(reflect.Type) []reflect.StructField
 
+	// LookupComment allows customizing comment lookup. Given a reflect.Type and optionally
+	// a field name, it should return the comment string associated with this type or field.
+	//
+	// If the field name is empty, it should return the type's comment; otherwise, the field's
+	// comment should be returned. If no comment is found, an empty string should be returned.
+	//
+	// When set, this function is called before the below CommentMap lookup mechanism. However,
+	// if it returns an empty string, the CommentMap is still consulted.
+	LookupComment func(reflect.Type, string) string
+
 	// CommentMap is a dictionary of fully qualified go types and fields to comment
 	// strings that will be used if a description has not already been provided in
 	// the tags. Types and fields are added to the package path using "." as a
@@ -156,7 +166,7 @@ type Reflector struct {
 	//
 	//   map[string]string{"github.com/invopop/jsonschema.Reflector.DoNotReference": "Do not reference definitions."}
 	//
-	// See also: AddGoComments
+	// See also: AddGoComments, LookupComment
 	CommentMap map[string]string
 }
 
@@ -558,19 +568,6 @@ func appendUniqueString(base []string, value string) []string {
 	return append(base, value)
 }
 
-func (r *Reflector) lookupComment(t reflect.Type, name string) string {
-	if r.CommentMap == nil {
-		return ""
-	}
-
-	n := fullyQualifiedTypeName(t)
-	if name != "" {
-		n = n + "." + name
-	}
-
-	return r.CommentMap[n]
-}
-
 // addDefinition will append the provided schema. If needed, an ID and anchor will also be added.
 func (r *Reflector) addDefinition(definitions Definitions, t reflect.Type, s *Schema) {
 	name := r.typeName(t)

reflect_comments.go

@@ -5,6 +5,7 @@ import (
 	"io/fs"
 	gopath "path"
 	"path/filepath"
+	"reflect"
 	"strings"
 
 	"go/ast"
@@ -124,3 +125,22 @@ func (r *Reflector) extractGoComments(base, path string, commentMap map[string]s
 
 	return nil
 }
+
+func (r *Reflector) lookupComment(t reflect.Type, name string) string {
+	if r.LookupComment != nil {
+		if comment := r.LookupComment(t, name); comment != "" {
+			return comment
+		}
+	}
+
+	if r.CommentMap == nil {
+		return ""
+	}
+
+	n := fullyQualifiedTypeName(t)
+	if name != "" {
+		n = n + "." + name
+	}
+
+	return r.CommentMap[n]
+}

reflect_comments_test.go

@@ -1,12 +1,15 @@
 package jsonschema
 
 import (
+	"fmt"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"testing"
 
-	"github.com/invopop/jsonschema/examples"
 	"github.com/stretchr/testify/require"
+
+	"github.com/invopop/jsonschema/examples"
 )
 
 func TestCommentsSchemaGeneration(t *testing.T) {
@@ -17,6 +20,7 @@ func TestCommentsSchemaGeneration(t *testing.T) {
 	}{
 		{&examples.User{}, prepareCommentReflector(t), "fixtures/go_comments.json"},
 		{&examples.User{}, prepareCommentReflector(t, WithFullComment()), "fixtures/go_comments_full.json"},
+		{&examples.User{}, prepareCustomCommentReflector(t), "fixtures/custom_comments.json"},
 	}
 	for _, tt := range tests {
 		name := strings.TrimSuffix(filepath.Base(tt.fixture), ".json")
@@ -35,3 +39,23 @@ func prepareCommentReflector(t *testing.T, opts ...CommentOption) *Reflector {
 	require.NoError(t, err, "did not expect error while adding comments")
 	return r
 }
+
+func prepareCustomCommentReflector(t *testing.T) *Reflector {
+	t.Helper()
+	r := new(Reflector)
+	r.LookupComment = func(t reflect.Type, f string) string {
+		if t != reflect.TypeOf(examples.User{}) {
+			// To test the interaction between a custom LookupComment function and the
+			// AddGoComments function, we only override comments for the User type.
+			return ""
+		}
+		if f == "" {
+			return fmt.Sprintf("Go type %s, defined in package %s.", t.Name(), t.PkgPath())
+		}
+		return fmt.Sprintf("Field %s of Go type %s.%s.", f, t.PkgPath(), t.Name())
+	}
+	// Also add the Go comments.
+	err := r.AddGoComments("github.com/invopop/jsonschema", "./examples")
+	require.NoError(t, err, "did not expect error while adding comments")
+	return r
+}