Don't drop to newline when serializing patterns starting with special chars

fluent.syntax/src/main/kotlin/org/projectfluent/syntax/serializer/Serializer.kt

@@ -2,11 +2,33 @@ package org.projectfluent.syntax.serializer
 
 import org.projectfluent.syntax.ast.* // ktlint-disable no-wildcard-imports
 
-private fun indent(content: CharSequence) = content.split("\n").joinToString("\n    ")
+private fun indentExceptFirstLine(content: CharSequence) =
+    content.split("\n").joinToString("\n    ")
+
+private fun PatternElement.includesLine() =
+    this is TextElement && value.contains("\n")
+
+private fun PatternElement.isSelectExpr() =
+    this is Placeable && expression is SelectExpression
+
+private fun Pattern.shouldStartOnNewLine(): Boolean {
+    val isMultiline = this.elements.any { it.isSelectExpr() || it.includesLine() }
+    if (isMultiline) {
+        val firstElement = this.elements.elementAtOrNull(0)
+        if (firstElement is TextElement) {
+            val firstChar = firstElement.value.elementAtOrNull(0)
+            // Due to the indentation requirement the following characters may not appear
+            // as the first character on a new line.
+            if (firstChar == '[' || firstChar == '.' || firstChar == '*') {
+                return false
+            }
+        }
 
-private fun PatternElement.includesLine() = this is TextElement && value.contains("\n")
+        return true
+    }
 
-private fun PatternElement.isSelectExpr() = this is Placeable && expression is SelectExpression
+    return false
+}
 
 /**
  * Serialize Fluent nodes to `CharSequence`.
@@ -117,16 +139,15 @@ class FluentSerializer(private val withJunk: Boolean = false) {
     }
 
     private fun serializeAttribute(attribute: Attribute): CharSequence {
-        val value = indent(serializePattern(attribute.value))
+        val value = indentExceptFirstLine(serializePattern(attribute.value))
         return "\n    .${attribute.id.name} =$value"
     }
 
     private fun serializePattern(pattern: Pattern): CharSequence {
-        val startOnLine = pattern.elements.any { it.isSelectExpr() || it.includesLine() }
         val elements = pattern.elements.map(::serializeElement)
-        val content = indent(elements.joinToString(""))
+        val content = indentExceptFirstLine(elements.joinToString(""))
 
-        return if (startOnLine) {
+        return if (pattern.shouldStartOnNewLine()) {
             "\n    $content"
         } else {
             " $content"
@@ -187,7 +208,7 @@ class FluentSerializer(private val withJunk: Boolean = false) {
 
     private fun serializeVariant(variant: Variant): CharSequence {
         val key = serializeVariantKey(variant.key)
-        val value = indent(serializePattern(variant.value))
+        val value = indentExceptFirstLine(serializePattern(variant.value))
 
         return if (variant.default) {
             "\n   *[$key]$value"

fluent.syntax/src/test/kotlin/org/projectfluent/syntax/serializer/SerializeResourceTest.kt

@@ -202,6 +202,35 @@ class SerializeResourceTest {
         assertEquals(input, this.pretty(input))
     }
 
+    @Test
+    fun multiline_starting_inline() {
+        val input =
+            """
+            foo = Foo
+                Baz
+
+            """.trimIndent()
+        val output =
+            """
+            foo =
+                Foo
+                Baz
+
+            """.trimIndent()
+        assertEquals(output, this.pretty(input))
+    }
+
+    @Test
+    fun multiline_starting_inline_with_a_special_char() {
+        val input =
+            """
+            foo = *Foo
+                Baz
+
+            """.trimIndent()
+        assertEquals(input, this.pretty(input))
+    }
+
     @Test
     fun multiline_with_placeable() {
         val input =
@@ -378,6 +407,19 @@ class SerializeResourceTest {
         assertEquals(expected, this.pretty(input))
     }
 
+    @Test
+    fun select_expression_in_inline_pattern_starting_with_a_special_char() {
+        val input =
+            """
+            foo = .Foo { ${'$'}sel ->
+                   *[a] A
+                    [b] B
+                }
+
+            """.trimIndent()
+        assertEquals(input, this.pretty(input))
+    }
+
     @Test
     fun select_expression_in_multiline_pattern() {
         val input =

fluent.syntax/src/test/resources/reference_fixtures/special_chars.ftl

@@ -0,0 +1,14 @@
+## OK
+
+bracket-inline = [Value]
+dot-inline = .Value
+star-inline = *Value
+
+## ERRORS
+
+bracket-newline =
+    [Value]
+dot-newline =
+    .Value
+star-newline =
+    *Value

fluent.syntax/src/test/resources/reference_fixtures/special_chars.json

@@ -0,0 +1,82 @@
+{
+    "type": "Resource",
+    "body": [
+        {
+            "type": "GroupComment",
+            "content": "OK"
+        },
+        {
+            "type": "Message",
+            "id": {
+                "type": "Identifier",
+                "name": "bracket-inline"
+            },
+            "value": {
+                "type": "Pattern",
+                "elements": [
+                    {
+                        "type": "TextElement",
+                        "value": "[Value]"
+                    }
+                ]
+            },
+            "attributes": [],
+            "comment": null
+        },
+        {
+            "type": "Message",
+            "id": {
+                "type": "Identifier",
+                "name": "dot-inline"
+            },
+            "value": {
+                "type": "Pattern",
+                "elements": [
+                    {
+                        "type": "TextElement",
+                        "value": ".Value"
+                    }
+                ]
+            },
+            "attributes": [],
+            "comment": null
+        },
+        {
+            "type": "Message",
+            "id": {
+                "type": "Identifier",
+                "name": "star-inline"
+            },
+            "value": {
+                "type": "Pattern",
+                "elements": [
+                    {
+                        "type": "TextElement",
+                        "value": "*Value"
+                    }
+                ]
+            },
+            "attributes": [],
+            "comment": null
+        },
+        {
+            "type": "GroupComment",
+            "content": "ERRORS"
+        },
+        {
+            "type": "Junk",
+            "annotations": [],
+            "content": "bracket-newline =\n    [Value]\n"
+        },
+        {
+            "type": "Junk",
+            "annotations": [],
+            "content": "dot-newline =\n    .Value\n"
+        },
+        {
+            "type": "Junk",
+            "annotations": [],
+            "content": "star-newline =\n    *Value\n"
+        }
+    ]
+}