Allow exprs in the source_file grammar rule

Summary:
Closes WhatsApp/tree-sitter-erlang#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)

X-link: WhatsApp/tree-sitter-erlang#9

Reviewed By: michalmuskala

Differential Revision: D69120163

Pulled By: alanz

fbshipit-source-id: 73f02ac6b61dbd0bec100d2dcfaa52b7694304cb

crates/syntax/src/ast/generated/nodes.rs

@@ -5615,6 +5615,9 @@ pub struct SourceFile {
     pub(crate) syntax: SyntaxNode,
 }
 impl SourceFile {
+    pub fn exprs(&self) -> AstChildren<Expr> {
+        support::children(&self.syntax)
+    }
     pub fn forms_only(&self) -> AstChildren<Form> {
         support::children(&self.syntax)
     }

crates/syntax/src/lib.rs

@@ -459,38 +459,42 @@ mod tests {
 
     #[test]
     fn error_nodes1() {
+        // Note: even though the FUN_DECL is in an ERROR node, we
+        // still lower it into something we can use.  See test
+        // body::tests::lowering_with_error_nodes
         check_node(
             "f(1a) -> ok begin 1 end.",
             expect![[r#"
                 [email protected]
-                  FUN_DECL@0..11
-                    FUNCTION_CLAUSE@0..11
-                      ATOM@0..1
-                        [email protected] "f"
-                      [email protected]
-                        ANON_LPAREN@1..2 "("
-                        [email protected]
-                          INTEGER@2..3
-                            [email protected] "1"
-                        [email protected]
-                          [email protected] "a"
-                        [email protected] ")"
-                      [email protected] " "
-                      [email protected]
-                        ANON_DASH_GT@6..8 "->"
-                        [email protected] " "
-                        [email protected]
-                          [email protected] "ok"
-                  [email protected] " "
-                  [email protected]
+                  ERROR@0..17
+                    FUN_DECL@0..11
+                      FUNCTION_CLAUSE@0..11
+                        [email protected]
+                          [email protected] "f"
+                        EXPR_ARGS@1..5
+                          [email protected] "("
+                          ERROR@2..3
+                            [email protected]
+                              [email protected] "1"
+                          [email protected]
+                            [email protected] "a"
+                          [email protected] ")"
+                        [email protected] " "
+                        CLAUSE_BODY@6..11
+                          [email protected] "->"
+                          [email protected] " "
+                          [email protected]
+                            [email protected] "ok"
+                    [email protected] " "
                     [email protected]
                       [email protected] "begin"
-                    [email protected] " "
-                    [email protected]
-                      [email protected] "1"
-                    [email protected] " "
-                    [email protected] "end"
-                    [email protected] ".""#]],
+                  [email protected] " "
+                  [email protected]
+                    [email protected] "1"
+                  [email protected] " "
+                  [email protected]
+                    [email protected] "end"
+                  [email protected] ".""#]],
         );
     }
 

crates/syntax/src/syntax_kind/generated.rs

@@ -56,7 +56,7 @@ pub enum SyntaxKind {
     CATCH_EXPR = 202u16,
     CHAR = 133u16,
     CLAUSE_BODY = 200u16,
-    ANON_COLON = 3u16,
+    ANON_COLON = 4u16,
     ANON_COLON_COLON = 62u16,
     ANON_COLON_EQ = 95u16,
     ANON_COMMA = 30u16,
@@ -78,7 +78,7 @@ pub enum SyntaxKind {
     DEPRECATED_WILDCARD = 57u16,
     DEPRECATION_DESC = 170u16,
     ANON_DIV = 106u16,
-    ANON_DOT = 4u16,
+    ANON_DOT = 2u16,
     ANON_DOT_DOT = 73u16,
     DOTDOTDOT = 74u16,
     ANON_ELIF = 26u16,
@@ -216,7 +216,7 @@ pub enum SyntaxKind {
     SOURCE_FILE = 138u16,
     SPEC = 180u16,
     ANON_SPEC = 65u16,
-    ANON_SSR = 2u16,
+    ANON_SSR = 3u16,
     SSR_DEFINITION = 140u16,
     ANON_SSR_MATCH = 5u16,
     SSR_REPLACEMENT = 141u16,