From: Ronan Dunklau <ronan.dunklau@aiven.io>
Date: Fri, 13 Aug 2021 15:03:18 +0200
Subject: [PATCH v6 1/5] Add ErrorTag support

---
 src/backend/utils/error/elog.c | 48 ++++++++++++++++++++++++++++++++++
 src/include/utils/elog.h       | 10 +++++++
 2 files changed, 58 insertions(+)

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 7402696986..4fb4c67c3f 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -460,6 +460,7 @@ errstart(int elevel, const char *domain)
 		edata->sqlerrcode = ERRCODE_SUCCESSFUL_COMPLETION;
 	/* errno is saved here so that error parameter eval can't change it */
 	edata->saved_errno = errno;
+	edata->tags = NIL;
 
 	/*
 	 * Any allocations for this error state level should go into ErrorContext
@@ -511,6 +512,7 @@ errfinish(const char *filename, int lineno, const char *funcname)
 	int			elevel;
 	MemoryContext oldcontext;
 	ErrorContextCallback *econtext;
+	ListCell   *lc;
 
 	recursion_depth++;
 	CHECK_STACK_DEPTH();
@@ -616,7 +618,18 @@ errfinish(const char *filename, int lineno, const char *funcname)
 		pfree(edata->constraint_name);
 	if (edata->internalquery)
 		pfree(edata->internalquery);
+	/* Every tag should have been palloc'ed */
+	if (edata->tags != NIL)
+	{
+		foreach(lc, edata->tags)
+		{
+			ErrorTag   *tag = (ErrorTag *) lfirst(lc);
 
+			pfree(tag->tagvalue);
+			pfree(tag);
+		}
+		pfree(edata->tags);
+	}
 	errordata_stack_depth--;
 
 	/* Exit error-handling context */
@@ -1187,6 +1200,41 @@ errhint_plural(const char *fmt_singular, const char *fmt_plural,
 	return 0;					/* return value does not matter */
 }
 
+int
+errtag(const char *tag, const char *fmt_value,...)
+{
+	ErrorData  *edata = &errordata[errordata_stack_depth];
+	ErrorTag   *etag;
+	MemoryContext oldcontext;
+	StringInfoData buf;
+
+	recursion_depth++;
+	CHECK_STACK_DEPTH();
+	oldcontext = MemoryContextSwitchTo(edata->assoc_context);
+	etag = palloc(sizeof(ErrorTag));
+	etag->tagname = tag;
+	initStringInfo(&buf);
+	for (;;)
+	{
+		va_list		args;
+		int			needed;
+
+		errno = edata->saved_errno;
+		va_start(args, fmt_value);
+		needed = appendStringInfoVA(&buf, fmt_value, args);
+		va_end(args);
+		if (needed == 0)
+			break;
+		enlargeStringInfo(&buf, needed);
+	}
+	etag->tagvalue = pstrdup(buf.data);
+	edata->tags = lappend(edata->tags, etag);
+	pfree(buf.data);
+	MemoryContextSwitchTo(oldcontext);
+	recursion_depth--;
+	return 0;
+}
+
 
 /*
  * errcontext_msg --- add a context error message text to the current error
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.h
index 3eb8de3966..615fae47ef 100644
--- a/src/include/utils/elog.h
+++ b/src/include/utils/elog.h
@@ -15,6 +15,7 @@
 #define ELOG_H
 
 #include <setjmp.h>
+#include "nodes/pg_list.h"
 
 /* Error level codes */
 #define DEBUG5		10			/* Debugging messages, in categories of
@@ -193,6 +194,8 @@ extern int	errhint(const char *fmt,...) pg_attribute_printf(1, 2);
 extern int	errhint_plural(const char *fmt_singular, const char *fmt_plural,
 						   unsigned long n,...) pg_attribute_printf(1, 4) pg_attribute_printf(2, 4);
 
+extern int	errtag(const char *tag, const char *fmt_value,...) pg_attribute_printf(2, 3);
+
 /*
  * errcontext() is typically called in error context callback functions, not
  * within an ereport() invocation. The callback function can be in a different
@@ -395,11 +398,18 @@ typedef struct ErrorData
 	int			internalpos;	/* cursor index into internalquery */
 	char	   *internalquery;	/* text of internally-generated query */
 	int			saved_errno;	/* errno at entry */
+	List	   *tags;			/* List of error tags */
 
 	/* context containing associated non-constant strings */
 	struct MemoryContextData *assoc_context;
 } ErrorData;
 
+typedef struct ErrorTag
+{
+	const char *tagname;
+	char	   *tagvalue;
+} ErrorTag;
+
 extern void EmitErrorReport(void);
 extern ErrorData *CopyErrorData(void);
 extern void FreeErrorData(ErrorData *edata);
-- 
2.34.1


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