Initial commit

Author: asgerf

.gitignore

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+/node_modules/
+/build
+.DS_Store

LICENSE

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+Copyright 2020 Asger Feldthaus
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

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+# dts-tree-sitter
+
+**dts-tree-sitter** generates TypeScript `.d.ts` files for interacting the AST from a given tree-sitter grammar.
+
+## Usage
+
+```sh
+npm i @asgerf/dts-tree-sitter
+
+npx @asgerf/dts-tree-sitter INPUT > OUTPUT.d.ts
+```
+
+where `INPUT` is used to locate a `node-types.json` file in one of the following locations:
+- `${INPUT}`
+- `${INPUT}/node-types.json`
+- `${INPUT}/src/node-types.json`
+- `node_modules/${INPUT}/src/node-types.json`
+
+## Example
+
+The `tree-sitter-javascript` grammar can be compiled like this:
+```sh
+npm i tree-sitter-javascript
+npx @asgerf/dts-tree-sitter tree-sitter-javascript > generated.d.ts
+```
+
+In the resulting grammar, two of the node types look like this:
+```ts
+export interface ClassDeclarationNode extends SyntaxNodeBase {
+  type: SyntaxType.ClassDeclaration;
+  bodyNode: ClassBodyNode;
+  decoratorNodes?: DecoratorNode[];
+  nameNode: IdentifierNode;
+}
+
+export interface ClassBodyNode extends SyntaxNodeBase {
+  type: SyntaxType.ClassBody;
+  memberNodes?: (MethodDefinitionNode | PublicFieldDefinitionNode)[];
+}
+```
+
+This can be used like this (see [full example](examples/javascript/index.ts)):
+```ts
+import * as g from "./generated";
+
+function getMemberNames(node: g.ClassDeclarationNode) {
+    let result = [];
+    for (let member of node.bodyNode.memberNodes) {
+        if (member.type === g.SyntaxType.MethodDefinition) {
+            result.push(member.nameNode.text);
+        } else {
+            result.push(member.propertyNode.text);
+        }
+    }
+    return result;
+}
+```
+
+Observe TypeScript do its magic: the type check in the `if` promotes the type of `member` to a `MethodDefinitionNode`
+in the 'then' branch, and to `PublicFieldDefinitionNode` in the 'else' branch.
+
+## Typed Tree Cursors
+
+Tree sitter's `TreeCursor` allows fast traversal of an AST, and has two properties with correlated types: `nodeType`, and `currentNode`.
+Once you've checked `nodeType`, it's annoying to have to cast `currentNode` to the correponding type right afterwards:
+```ts
+if (cursor.nodeType === g.SyntaxType.Function) {
+  let node = cursor.currentNode as g.Function; // annoying cast
+}
+```
+
+There's another way, which is handy in large switches: Cast the cursor itself to a `TypedTreeCursor` before switching on `nodeType`.
+Then the guarded use of `currentNode` has the expected type. For example:
+```ts
+function printDeclaredNames() {
+    let cursor = tree.walk();
+    do {
+        const c = cursor as g.TypedTreeCursor;
+        switch (c.nodeType) {
+            case g.SyntaxType.ClassDeclaration:
+            case g.SyntaxType.FunctionDeclaration:
+            case g.SyntaxType.VariableDeclarator: {
+                let node = c.currentNode;
+                console.log(node.nameNode.text);
+                break;
+            }
+        }
+    } while(gotoPreorderSucc(cursor));
+}
+```
+- `node` gets the type `ClassDeclarationNode | FunctionDeclarationNode | VariableDeclaratorNode`.
+- This allows safe access to `node.nameNode`, since each of those types have a `name` field.
+- We don't pay the cost of invoking `currentNode` for other types of nodes.
+
+## Trouble-shooting
+
+### I get an error about "excessive stack depth" during compilation
+
+This happens if you compare types from the general `tree-sitter.d.ts` file with those from the generated `.d.ts` file.
+Every type from `tree-sitter.d.ts` has a stronger version in the generated file; make sure you don't mix and match.
+
+
+### I get `UnnamedNode` types in places where I don't expect them
+
+This can happen if the grammar contains rules and literals with the same name. For example this grammar rule,
+```js
+  func: $ => seq('func', $.name, $.body)
+```
+will produce a named node with type `func`, while the `'func'` literal will produce an unnamed node with type `func` as well.
+
+This means a check like `node.type === 'func'` is not an exact type check, and the type of `node` will only be restricted to `FuncNode | UnnamedNode<'func'>`. This is _not_ a bug in the generated `.d.ts` file: there really are two kinds of nodes you need to handle after that check.
+
+Some possible solutions are:
+- Change the grammar to avoid rules with the same name as a keyword.
+- Write the check as `node.isNamed && node.type === 'func'`.
+- Change the declared type of `node` from `SyntaxNode` to `NamedNode`.