Allow exprs in the source_file grammar rule (#9)

Summary:
Closes #3.

Currently, only "top level" forms of a module are allowed at the beginning of the source_file rule, but this makes this tree-sitter not usable, for example, in Markdown code blocks.

Allowing any fragment of an expression makes this tree-sitter usable for other languages to inject Erlang code, for example, a new language in the Phoenix (Elixir) style, that embeeds Erlang code in HTML.

 ---

Notes:

1. The tree generated for fragmented code is `(source_file (...exprs))`. Maybe the tree as is today as `(source_file (...forms))` should be for a file/module structure and `(fragment (...exprs))` should be for fragmented parts of code
2. The term "fragment" is what comes to my mind, but could be any other
3. I'm not sure about the conflicts order introduced by this PR

 ---

## Before this PR

![tree-sitter-erlang-before](https://github.com/user-attachments/assets/b922e440-8ca0-432e-845d-82ad6c532299)

## After this PR

![tree-sitter-erlang-after](https://github.com/user-attachments/assets/0a835a76-1a90-4d7c-b171-9e46c9c47301)

Pull Request resolved: #9

Test Plan:
Imported from GitHub, without a `Test Plan:` line.

- CI
- cd tree-sitter-erlang
- make
Ensure all tests pass, and no generated files change
- cd ..
- cargo xtask codegen
Check that no checked in files change
- Compare lint output before and after

```
cargo run --bin elp -- lint --project ~/fbsource/whatsapp/server/erl --include-erlc-diagnostics --include-edoc-diagnostics --read-config --include-tests --include-ct-diagnostics &> /tmp/run-elp-lint.txt
```
Check out master
```
cargo run --bin elp -- lint --project ~/fbsource/whatsapp/server/erl --include-erlc-diagnostics --include-edoc-diagnostics --read-config --include-tests --include-ct-diagnostics &> /tmp/run-elp-lint-master.txt
```

`diff /tmp/run-elp-lint.txt /tmp/run-elp-lint-master.txt` should show no differences

Reviewed By: michalmuskala

Differential Revision: D69120163

Pulled By: alanz

fbshipit-source-id: 73f02ac6b61dbd0bec100d2dcfaa52b7694304cb

Author: williamthome

grammar.js

@@ -25,17 +25,16 @@ const PREC = {
     ADD_OP: 5, // add_op is left-associative
     DOTDOT: 6, // `..` in Type
     DARROW: 7, // `=>` in Type, Expr
-    CEQ: 8, // `:=` in Type, Expr
-    BANG: 13, // `:=` in Expr
-    ORELSE: 14, // `:=` in Expr
-    ANDALSO: 15, // `:=` in Expr
-    LIST_OP: 16, // `:=` in Expr
-    COMP_OP: 17, // `:=` in Expr
+    BANG: 13, // `!` in Expr
+    ORELSE: 14, // `orelse` in Expr
+    ANDALSO: 15, // `andalso` in Expr
+    LIST_OP: 16, // `++` / `--` in Expr
+    COMP_OP: 17, // Comparison operators in Expr
 
     // For remote vs binary :
-    CALL: 80,
     REMOTE: 1,
     BIT_EXPR: 2,
+    CALL: 80,
 
     COND_MATCH: 81, // `?=` in maybe expr. Should has lowest priority https://www.erlang.org/eeps/eep-0049#operator-priority
 
@@ -46,6 +45,12 @@ const PREC = {
     DYN_GUARD_AND: 4,
     DYN_EXPR_GUARD: 5,
     DYN_EXPR: 6,
+
+    // Distinguishing between top level forms and expressions.
+    // Given a form *has* to be at the top level (only), we give the
+    // form construct a higher precedence each time.
+    PP_IF: 20, // Conflict between `pp_if` and `_prefix_op`
+    ATTR_NAME: 20, // Conflict between `attr_name` and `_prefix_op`
 };
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -182,11 +187,19 @@ module.exports = grammar({
         [$._macro_def_replacement, $.replacement_guard_and, $.replacement_expr_guard],
         // Fun type vs regular function `fun()` vs `fun() -> ...`
         [$.fun_type, $.expr_args],
+        // Introduced by the exprs choice in the source_file
+        [$._expr, $._map_expr_base, $._record_expr_base],
+        [$._expr, $._map_expr_base],
+        [$._expr, $._record_expr_base],
+        [$._function_or_macro_clause, $._macro_body_expr],
     ],
 
     rules: {
 
-        source_file: $ => field('forms_only', repeat($._form)),
+        source_file: $ => choice(
+            field('forms_only', repeat($._form)),
+            field('exprs', repeat(seq($._expr, optional("."))))
+        ),
 
         // -------------------------------------------------------------
 
@@ -258,7 +271,7 @@ module.exports = grammar({
         pp_ifndef: $ => seq('-', atom_const('ifndef'), '(', field("name", $._macro_name), ')', '.'),
         pp_else: $ => seq('-', atom_const('else'), '.'),
         pp_endif: $ => seq('-', atom_const('endif'), '.'),
-        pp_if: $ => seq('-', atom_const('if'), field("cond", $._expr), '.'),
+        pp_if: $ => prec(PREC.PP_IF, seq('-', atom_const('if'), field("cond", $._expr), '.')),
         pp_elif: $ => seq('-', atom_const('elif'), field("cond", $._expr), '.'),
 
         pp_define: $ => seq(
@@ -436,7 +449,7 @@ module.exports = grammar({
 
         wild_attribute: $ => seq(field("name", $.attr_name), field("value", $._expr), '.'),
 
-        attr_name: $ => seq('-', field("name", $._name)),
+        attr_name: $ => prec(PREC.ATTR_NAME, seq('-', field("name", $._name))),
 
         fun_decl: $ => prec.right(seq(
             field("clause", $._function_or_macro_clause),

package.json

@@ -6,6 +6,7 @@
     "install": "node-gyp-build",
     "prestart": "tree-sitter build --wasm",
     "start": "tree-sitter playground",
+    "parse": "npx tree-sitter-cli parse",
     "test": "node --test bindings/node/*_test.js"
   },
   "authors": [