From 09d24205084a1ee63aaef63c3823dd68a7d513a5 Mon Sep 17 00:00:00 2001
From: Corey Johnson <probablycorey@gmail.com>
Date: Mon, 24 Nov 2025 16:04:03 -0800
Subject: [PATCH] add some arg help

---
 vscode-extension/server/src/server.ts        |  11 ++
 vscode-extension/server/src/signatureHelp.ts | 105 +++++++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 vscode-extension/server/src/signatureHelp.ts

diff --git a/vscode-extension/server/src/server.ts b/vscode-extension/server/src/server.ts
index 9177abb..5feacd9 100644
--- a/vscode-extension/server/src/server.ts
+++ b/vscode-extension/server/src/server.ts
@@ -2,6 +2,7 @@ import { TextDocument } from 'vscode-languageserver-textdocument'
 import { buildDiagnostics } from './diagnostics'
 import { buildSemanticTokens, TOKEN_MODIFIERS, TOKEN_TYPES } from './semanticTokens'
 import { provideCompletions } from './completion/completionProvider'
+import { provideSignatureHelp } from './signatureHelp'
 import { PRELUDE_NAMES } from './metadata/prelude-names'
 import { parser } from '../../../src/parser/shrimp'
 import { setGlobals } from '../../../src/parser/tokenizer'
@@ -29,6 +30,7 @@ connection.onInitialize(handleInitialize)
 connection.languages.semanticTokens.on(handleSemanticTokens)
 documents.onDidChangeContent(handleDocumentChange)
 connection.onCompletion(handleCompletion)
+connection.onSignatureHelp(handleSignatureHelp)
 
 // Debug commands
 connection.onRequest('shrimp/parseTree', handleParseTree)
@@ -49,6 +51,9 @@ function handleInitialize(): InitializeResult {
       completionProvider: {
         triggerCharacters: ['.'],
       },
+      signatureHelpProvider: {
+        triggerCharacters: [' '],
+      },
       semanticTokensProvider: {
         legend: {
           tokenTypes: TOKEN_TYPES,
@@ -113,6 +118,12 @@ function handleCompletion(params: any) {
   return [...keywordCompletions, ...preludeCompletions]
 }
 
+function handleSignatureHelp(params: any) {
+  const document = documents.get(params.textDocument.uri)
+  if (!document) return
+  return provideSignatureHelp(document, params.position)
+}
+
 function handleParseTree(params: { uri: string }) {
   connection.console.log(`🦐 Parse tree requested for: ${params.uri}`)
   const document = documents.get(params.uri)
diff --git a/vscode-extension/server/src/signatureHelp.ts b/vscode-extension/server/src/signatureHelp.ts
new file mode 100644
index 0000000..b356397
--- /dev/null
+++ b/vscode-extension/server/src/signatureHelp.ts
@@ -0,0 +1,105 @@
+import { SignatureHelp, SignatureInformation, ParameterInformation } from 'vscode-languageserver/node'
+import { TextDocument } from 'vscode-languageserver-textdocument'
+import { Tree, SyntaxNode } from '@lezer/common'
+import { parser } from '../../../src/parser/shrimp'
+import { completions } from './metadata/prelude-completions'
+
+export const provideSignatureHelp = (
+  document: TextDocument,
+  position: { line: number; character: number }
+): SignatureHelp | undefined => {
+  const text = document.getText()
+  const tree = parser.parse(text)
+  const cursorPos = document.offsetAt(position)
+
+  const context = findCallContext(tree, cursorPos, text)
+  if (!context) return
+
+  const params = lookupFunctionParams(context.funcName)
+  if (!params) return
+
+  return {
+    signatures: [buildSignature(context.funcName, params)],
+    activeParameter: Math.min(context.argCount, params.length - 1),
+  }
+}
+
+const findCallContext = (tree: Tree, cursorPos: number, text: string) => {
+  const findBestCall = (node: SyntaxNode): SyntaxNode | undefined => {
+    let result: SyntaxNode | undefined
+
+    const isCall = node.name === 'FunctionCall' || node.name === 'FunctionCallOrIdentifier'
+
+    // Call ends just before cursor (within 5 chars)
+    if (isCall && node.to <= cursorPos && cursorPos <= node.to + 5) {
+      result = node
+    }
+
+    // Cursor is inside the call's span
+    if (isCall && node.from < cursorPos && cursorPos < node.to) {
+      result = node
+    }
+
+    // Recurse - prefer smaller spans (more specific)
+    let child = node.firstChild
+    while (child) {
+      const found = findBestCall(child)
+      if (found) {
+        const foundSpan = found.to - found.from
+        const resultSpan = result ? result.to - result.from : Infinity
+        if (foundSpan < resultSpan) {
+          result = found
+        }
+      }
+      child = child.nextSibling
+    }
+
+    return result
+  }
+
+  const call = findBestCall(tree.topNode)
+  if (!call) return
+
+  // Count args before cursor
+  let argCount = 0
+  let child = call.firstChild
+  while (child) {
+    if ((child.name === 'PositionalArg' || child.name === 'NamedArg') && child.to <= cursorPos) {
+      argCount++
+    }
+    child = child.nextSibling
+  }
+
+  // Extract function name
+  const firstChild = call.firstChild
+  if (!firstChild) return
+
+  let funcName: string | undefined
+  if (firstChild.name === 'DotGet') {
+    funcName = text.slice(firstChild.from, firstChild.to)
+  } else if (firstChild.name === 'Identifier') {
+    funcName = text.slice(firstChild.from, firstChild.to)
+  }
+
+  if (!funcName) return
+
+  return { funcName, argCount }
+}
+
+const lookupFunctionParams = (funcName: string): string[] | undefined => {
+  // Handle module functions: "list.map" → modules.list.map
+  if (funcName.includes('.')) {
+    const [moduleName, methodName] = funcName.split('.')
+    const module = completions.modules[moduleName as keyof typeof completions.modules]
+    const method = module?.[methodName as keyof typeof module]
+    return method?.params as string[] | undefined
+  }
+
+  // TODO: Handle top-level prelude functions (print, range, etc.)
+}
+
+const buildSignature = (funcName: string, params: string[]): SignatureInformation => {
+  const label = `${funcName}(${params.join(', ')})`
+  const parameters: ParameterInformation[] = params.map(p => ({ label: p }))
+  return { label, parameters }
+}