SourceMgr: simplify API, keep file contents in memory, faster SrcLoc conversion

- add `string_buffer.Buf.detach()` to get buffer with ownership
- add `File.detach()` to get buffer with ownership
- simplify `string_buffer.Buf.newline()`
- add `File.is_const` and `SourceMgr.addResource()` for static contents
- unify `File` contents as `File.data_`/`File.data_size`
- improve `CheckPoint` system (simpler and much faster)
- remove `Max_open_files`
- remove `close_oldest()`, all files stay in memory until `clear()` or `free()`.

Author: chqrlie

ast_utils/constants.c2

@@ -29,8 +29,6 @@ public const u32 MaxMultiDecl = (1 << MaxMultiDeclBits) - 1;
 
 public const u32 Max_path = 512;
 
-public const u32 Max_open_files = 200;
-
 public const char* output_dir = "output";
 
 public const char* recipe_name = "recipe.txt";

ast_utils/string_buffer.c2

@@ -73,6 +73,23 @@ public fn const u8* Buf.udata(const Buf* buf) {
     return (u8*)buf.data_;
 }
 
+public fn void* Buf.detach(Buf* buf, u32 *psize) {
+    *psize = buf.size_;
+    if (buf.own) {
+        // try and shrink allocated buffer
+        void* data = realloc(buf.data_, buf.size_ + 1);
+        if (!data) data = buf.data_;
+        buf.data_ = nil;
+        buf.size_ = 0;
+        buf.capacity = 0;
+        buf.own = false;
+        return data;
+    } else {
+        void* data = malloc(buf.size_ + 1);
+        return memcpy(data, buf.data_, buf.size_ + 1);
+    }
+}
+
 public fn void Buf.clear(Buf* buf) {
     buf.size_ = 0;
 }
@@ -97,7 +114,6 @@ public fn void Buf.add(Buf* buf, const char* text) {
     buf.add2(text, len);
 }
 
-// len = strlen(text)
 public fn void Buf.add2(Buf* buf, const char* text, u32 len) {
     if (buf.size_ + len + 1 > buf.capacity) {
         u32 new_cap = buf.capacity * 2;
@@ -109,21 +125,9 @@ public fn void Buf.add2(Buf* buf, const char* text, u32 len) {
     buf.data_[buf.size_] = '\0';
 }
 
-public fn void Buf.newline(Buf* buf) {
-    if (buf.size_ + 2 > buf.capacity) {
-        u32 new_cap = buf.capacity * 2;
-        while (buf.size_ + 2 > new_cap) new_cap *= 2;
-        buf.resize(new_cap);
-    }
-    buf.data_[buf.size_] = '\n';
-    buf.size_ += 1;
-    buf.data_[buf.size_] = 0;
-}
-
+public fn void Buf.newline(Buf* buf) { buf.add1('\n'); }
 public fn void Buf.space(Buf* buf) { buf.add1(' '); }
-
 public fn void Buf.lparen(Buf* buf) { buf.add1('('); }
-
 public fn void Buf.rparen(Buf* buf) { buf.add1(')'); }
 
 public fn void Buf.print(Buf* buf, const char* format @(printf_format), ...) {

common/file/reader.c2

@@ -111,7 +111,7 @@ public fn void Reader.close(Reader* file) {
     }
 }
 
-public fn bool Reader.isOpen(const Reader* file) {
+public fn bool Reader.isOpen(const Reader* file) @(unused) {
     return file.region != nil;
 }
 
@@ -145,3 +145,11 @@ public fn const char* Reader.getError(const Reader* file) @(unused) {
     }
     return msg;
 }
+
+public fn void* Reader.detach(Reader* file, u32 *psize) {
+    void* data = file.region;
+    *psize = file.size;
+    file.region = nil;
+    file.size = 0;
+    return data;
+}