util: Add a string buffer implementation

Based on Vladislav Egorovs work on the preprocessor, but split
out to a util functionality that should be universal. Setup, teardown,
memory handling and general layout is modeled around the hash_table
and the set, to make it familiar for everyone.

A notable change is that this implementation is always null terminated.
The rationale is that it will be less error-prone, as one might
access the buffer directly, thereby reading a non-terminated string.
Also, vsnprintf and friends prints the null-terminator.

Signed-off-by: Thomas Helland <thomashelland90@gmail.com>
Tested-by: Dieter Nützel <Dieter at nuetzel-hh.de>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

V2: Address review feedback from Timothy and Grazvydas
   - Fix MINGW preprocessor check
   - Changed len from uint to int
   - Make string argument const in append function
   - Move to header and inline append function
   - Add crimp_to_fit function for resizing buffer

V3: Move include of ralloc to string_buffer.h

V4: Use u_string.h for a cross-platform working vsnprintf

V5: Remember to cast to char * in crimp function

V6: Address review feedback from Nicolai
   - Handle !str->buf in buffer_create
   - Ensure va_end is always called in buffer_append_all
   - Add overflow check in buffer_append_len
   - Do not expose buffer_space_left, just remove it
   - Clarify why a loop is used in vprintf, change to for-loop
   - Add a va_copy to buffer_vprintf to fix failure to append arguments
     when having to resize the buffer for vsnprintf.

V7: Address more review feedback from Nicolai
   - Add missing va_end corresponding to va_copy
   - Error check failure to allocate in crimp_to_fit

src/util/string_buffer.h

@@ -0,0 +1,104 @@
+/*
+ * Copyright © 2017 Thomas Helland
+ *
+ * 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 (including the next
+ * paragraph) 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.
+ *
+ */
+#ifndef _STRING_BUFFER_H
+#define _STRING_BUFFER_H
+
+#include "ralloc.h"
+#include "u_string.h"
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct _mesa_string_buffer {
+   char *buf;
+   uint32_t length;
+   uint32_t capacity;
+};
+
+struct _mesa_string_buffer *
+_mesa_string_buffer_create(void *mem_ctx, uint32_t initial_capacity);
+
+static inline void
+_mesa_string_buffer_destroy(struct _mesa_string_buffer *str)
+{
+   ralloc_free(str);
+}
+
+bool
+_mesa_string_buffer_append_all(struct _mesa_string_buffer *str,
+                               uint32_t num_args, ...);
+bool
+_mesa_string_buffer_append_len(struct _mesa_string_buffer *str,
+                               const char *c, uint32_t len);
+
+static inline bool
+_mesa_string_buffer_append_char(struct _mesa_string_buffer *str, char c)
+{
+   return _mesa_string_buffer_append_len(str, &c, 1);
+}
+
+static inline bool
+_mesa_string_buffer_append(struct _mesa_string_buffer *str, const char *c)
+{
+   return _mesa_string_buffer_append_len(str, c, strlen(c));
+}
+
+static inline void
+_mesa_string_buffer_clear(struct _mesa_string_buffer *str)
+{
+   str->length = 0;
+   str->buf[str->length] = '\0';
+}
+
+static inline void
+_mesa_string_buffer_crimp_to_fit(struct _mesa_string_buffer *str)
+{
+    char *crimped =
+       (char *) reralloc_array_size(str, str->buf, sizeof(char),
+                                    str->capacity);
+    if (!crimped)
+       return;
+
+    str->capacity = str->length + 1;
+    str->buf = crimped;
+}
+
+bool
+_mesa_string_buffer_vprintf(struct _mesa_string_buffer *str,
+                            const char *format, va_list args);
+
+bool
+_mesa_string_buffer_printf(struct _mesa_string_buffer *str,
+                            const char *format, ...);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* _STRING_BUFFER_H */