From 2a5409feab5ada09a8cce7a1fbcf74d6b9a76fd6 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Wed, 13 Mar 2019 09:22:09 -0700
Subject: [PATCH] Indicate in C API that highlight method doesn't mutate
 Highlighter

---
 highlight/include/tree_sitter/highlight.h |  2 +-
 highlight/src/c_lib.rs                    | 27 +++++++++++++++--------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/highlight/include/tree_sitter/highlight.h b/highlight/include/tree_sitter/highlight.h
index dd2f99c3..7b34aef9 100644
--- a/highlight/include/tree_sitter/highlight.h
+++ b/highlight/include/tree_sitter/highlight.h
@@ -75,7 +75,7 @@ int ts_highlighter_add_language(
 // Compute syntax highlighting for a given document. You must first
 // create a `TSHighlightBuffer` to hold the output.
 int ts_highlighter_highlight(
-  TSHighlighter *self,
+  const TSHighlighter *self,
   const char *scope_name,
   const char *source_code,
   uint32_t source_code_len,
diff --git a/highlight/src/c_lib.rs b/highlight/src/c_lib.rs
index 919da8c5..ce9f3936 100644
--- a/highlight/src/c_lib.rs
+++ b/highlight/src/c_lib.rs
@@ -31,7 +31,9 @@ pub enum ErrorCode {
 }
 
 #[no_mangle]
-pub extern "C" fn ts_highlighter_new(attribute_strings: *const *const c_char) -> *mut TSHighlighter {
+pub extern "C" fn ts_highlighter_new(
+    attribute_strings: *const *const c_char,
+) -> *mut TSHighlighter {
     let attribute_strings =
         unsafe { slice::from_raw_parts(attribute_strings, Scope::Unknown as usize + 1) };
     let attribute_strings = attribute_strings
@@ -69,25 +71,25 @@ pub extern "C" fn ts_highlight_buffer_delete(this: *mut TSHighlightBuffer) {
 }
 
 #[no_mangle]
-pub extern "C" fn ts_highlight_buffer_content(this: *mut TSHighlightBuffer) -> *const u8 {
+pub extern "C" fn ts_highlight_buffer_content(this: *const TSHighlightBuffer) -> *const u8 {
     let this = unwrap_ptr(this);
     this.html.as_slice().as_ptr()
 }
 
 #[no_mangle]
-pub extern "C" fn ts_highlight_buffer_line_offsets(this: *mut TSHighlightBuffer) -> *const u32 {
+pub extern "C" fn ts_highlight_buffer_line_offsets(this: *const TSHighlightBuffer) -> *const u32 {
     let this = unwrap_ptr(this);
     this.line_offsets.as_slice().as_ptr()
 }
 
 #[no_mangle]
-pub extern "C" fn ts_highlight_buffer_len(this: *mut TSHighlightBuffer) -> u32 {
+pub extern "C" fn ts_highlight_buffer_len(this: *const TSHighlightBuffer) -> u32 {
     let this = unwrap_ptr(this);
     this.html.len() as u32
 }
 
 #[no_mangle]
-pub extern "C" fn ts_highlight_buffer_line_count(this: *mut TSHighlightBuffer) -> u32 {
+pub extern "C" fn ts_highlight_buffer_line_count(this: *const TSHighlightBuffer) -> u32 {
     let this = unwrap_ptr(this);
     this.line_offsets.len() as u32
 }
@@ -100,7 +102,7 @@ pub extern "C" fn ts_highlighter_add_language(
     property_sheet_json: *const c_char,
     injection_regex: *const c_char,
 ) -> ErrorCode {
-    let this = unwrap_ptr(this);
+    let this = unwrap_mut_ptr(this);
     let scope_name = unsafe { CStr::from_ptr(scope_name) };
     let scope_name = unwrap(scope_name.to_str()).to_string();
     let property_sheet_json = unsafe { CStr::from_ptr(property_sheet_json) };
@@ -128,14 +130,14 @@ pub extern "C" fn ts_highlighter_add_language(
 
 #[no_mangle]
 pub extern "C" fn ts_highlighter_highlight(
-    this: *mut TSHighlighter,
+    this: *const TSHighlighter,
     scope_name: *const c_char,
     source_code: *const c_char,
     source_code_len: u32,
     output: *mut TSHighlightBuffer,
 ) -> ErrorCode {
     let this = unwrap_ptr(this);
-    let output = unwrap_ptr(output);
+    let output = unwrap_mut_ptr(output);
     let scope_name = unwrap(unsafe { CStr::from_ptr(scope_name).to_str() });
     let source_code =
         unsafe { slice::from_raw_parts(source_code as *const u8, source_code_len as usize) };
@@ -233,7 +235,14 @@ impl TSHighlightBuffer {
     }
 }
 
-fn unwrap_ptr<'a, T>(result: *mut T) -> &'a mut T {
+fn unwrap_ptr<'a, T>(result: *const T) -> &'a T {
+    unsafe { result.as_ref() }.unwrap_or_else(|| {
+        eprintln!("{}:{} - pointer must not be null", file!(), line!());
+        abort();
+    })
+}
+
+fn unwrap_mut_ptr<'a, T>(result: *mut T) -> &'a mut T {
     unsafe { result.as_mut() }.unwrap_or_else(|| {
         eprintln!("{}:{} - pointer must not be null", file!(), line!());
         abort();