Add basic BibTeX formatter

src/main/kotlin/texlab/BibtexFormatter.kt

@@ -0,0 +1,94 @@
+package texlab
+
+import texlab.syntax.bibtex.*
+
+object BibtexFormatter {
+    fun format(builder: StringBuilder, entry: BibtexEntrySyntax, settings: BibtexFormatterSettings) {
+        builder.append(entry.type.text)
+        builder.append("{")
+        builder.append(entry.name?.text ?: return)
+        builder.append(",")
+        builder.appendln()
+        for (field in entry.fields) {
+            format(builder, field, settings)
+        }
+        builder.append("}")
+    }
+
+    private fun format(builder: StringBuilder, field: BibtexFieldSyntax, settings: BibtexFormatterSettings) {
+        builder.append(settings.indent)
+        builder.append(field.name.text)
+        builder.append(" = ")
+        val startLength = settings.tabSize + field.name.text.length + 3
+
+        val tokens = getTokens(field.content ?: return)
+        builder.append(tokens[0].text)
+
+        var length = startLength + tokens[0].length
+        for (i in 1 until tokens.size) {
+            val previous = tokens[i - 1]
+            val current = tokens[i]
+
+            val insertSpace = shouldInsertSpace(previous, current)
+            val spaceLength = if (insertSpace) {
+                1
+            } else {
+                0
+            }
+
+            if (length + current.length + spaceLength > settings.lineLength) {
+                builder.appendln()
+                builder.append(settings.indent)
+                for (j in 0 until startLength - settings.tabSize + 1) {
+                    builder.append(" ")
+                }
+                length = startLength
+            } else if (insertSpace) {
+                builder.append(" ")
+                length++
+            }
+            builder.append(current.text)
+            length += current.length
+        }
+        builder.appendln(",")
+    }
+
+    private fun shouldInsertSpace(previous: BibtexToken, current: BibtexToken): Boolean {
+        if (previous.line != current.line) {
+            return true
+        }
+
+        return previous.end.character < current.start.character
+    }
+
+    private fun getTokens(content: BibtexContentSyntax): List<BibtexToken> {
+        val tokens = mutableListOf<BibtexToken>()
+        fun visit(node: BibtexContentSyntax) {
+            when (node) {
+                is BibtexWordSyntax -> {
+                    tokens.add(node.token)
+                }
+                is BibtexCommandSyntax -> {
+                    tokens.add(node.token)
+                }
+                is BibtexQuotedContentSyntax -> {
+                    tokens.add(node.left)
+                    node.children.forEach { visit(it) }
+                    node.right?.also { tokens.add(it) }
+                }
+                is BibtexBracedContentSyntax -> {
+                    tokens.add(node.left)
+                    node.children.forEach { visit(it) }
+                    node.right?.also { tokens.add(it) }
+                }
+                is BibtexConcatSyntax -> {
+                    visit(node.left)
+                    tokens.add(node.operator)
+                    node.right?.also { visit(it) }
+                }
+            }
+        }
+        visit(content)
+        return tokens
+    }
+}

src/main/kotlin/texlab/BibtexFormatterSettings.kt

@@ -0,0 +1,11 @@
+package texlab
+
+import java.util.*
+
+data class BibtexFormatterSettings(val insertSpaces: Boolean, val tabSize: Int, val lineLength: Int) {
+    val indent: String = if (insertSpaces) {
+        Collections.nCopies(tabSize, " ").joinToString("")
+    } else {
+        "\t"
+    }
+}

src/main/kotlin/texlab/LanguageServerImpl.kt

@@ -45,6 +45,7 @@ class LanguageServerImpl : LanguageServer {
             foldingRangeProvider = Either.forLeft(true)
             definitionProvider = true
             hoverProvider = true
+            documentFormattingProvider = true
         }
 
         return CompletableFuture.completedFuture(InitializeResult(capabilities))

src/main/kotlin/texlab/TextDocumentServiceImpl.kt

@@ -21,6 +21,7 @@ import texlab.metadata.CtanPackageMetadataProvider
 import texlab.metadata.PackageMetadataProvider
 import texlab.rename.*
 import texlab.symbol.*
+import texlab.syntax.bibtex.BibtexEntrySyntax
 import java.io.File
 import java.net.URI
 import java.nio.file.Paths
@@ -244,4 +245,24 @@ class TextDocumentServiceImpl(private val workspace: Workspace) : TextDocumentSe
             }
         }
     }
+
+    override fun formatting(params: DocumentFormattingParams): CompletableFuture<MutableList<out TextEdit>> {
+        synchronized(workspace) {
+            val uri = URI.create(params.textDocument.uri)
+            val document = workspace.documents
+                    .filterIsInstance<BibtexDocument>()
+                    .firstOrNull { it.uri == uri }
+                    ?: return CompletableFuture.completedFuture(null)
+
+            val settings = BibtexFormatterSettings(params.options.isInsertSpaces, params.options.tabSize, 120)
+
+            val edits = mutableListOf<TextEdit>()
+            for (entry in document.tree.root.children.filterIsInstance<BibtexEntrySyntax>()) {
+                val text = StringBuilder()
+                BibtexFormatter.format(text, entry, settings)
+                edits.add(TextEdit(entry.range, text.toString()))
+            }
+            return CompletableFuture.completedFuture(edits)
+        }
+    }
 }

src/main/kotlin/texlab/syntax/Token.kt

@@ -19,4 +19,7 @@ abstract class Token {
         get () = Range(start, end)
 
     abstract val text: String
+
+    val length: Int
+        get() = text.length
 }