Improve design and implementation of pg_file_settings view.

As first committed, this view reported on the file contents as they were
at the last SIGHUP event.  That's not as useful as reporting on the current
contents, and what's more, it didn't work right on Windows unless the
current session had serviced at least one SIGHUP.  Therefore, arrange to
re-read the files when pg_show_all_settings() is called.  This requires
only minor refactoring so that we can pass changeVal = false to
set_config_option() so that it won't actually apply any changes locally.

In addition, add error reporting so that errors that would prevent the
configuration files from being loaded, or would prevent individual settings
from being applied, are visible directly in the view.  This makes the view
usable for pre-testing whether edits made in the config files will have the
desired effect, before one actually issues a SIGHUP.

I also added an "applied" column so that it's easy to identify entries that
are superseded by later entries; this was the main use-case for the original
design, but it seemed unnecessarily hard to use for that.

Also fix a 9.4.1 regression that allowed multiple entries for a
PGC_POSTMASTER variable to cause bogus complaints in the postmaster log.
(The issue here was that commit bf007a27acd7b2fb unintentionally reverted
3e3f65973a3c94a6, which suppressed any duplicate entries within
ParseConfigFp.  However, since the original coding of the pg_file_settings
view depended on such suppression *not* happening, we couldn't have fixed
this issue now without first doing something with pg_file_settings.
Now we suppress duplicates by marking them "ignored" within
ProcessConfigFileInternal, which doesn't hide them in the view.)

Lesser changes include:

Drive the view directly off the ConfigVariable list, instead of making a
basically-equivalent second copy of the data.  There's no longer any need
to hang onto the data permanently, anyway.

Convert show_all_file_settings() to do its work in one call and return a
tuplestore; this avoids risks associated with assuming that the GUC state
will hold still over the course of query execution.  (I think there were
probably latent bugs here, though you might need something like a cursor
on the view to expose them.)

Arrange to run SIGHUP processing in a short-lived memory context, to
forestall process-lifespan memory leaks.  (There is one known leak in this
code, in ProcessConfigDirectory; it seems minor enough to not be worth
back-patching a specific fix for.)

Remove mistaken assignment to ConfigFileLineno that caused line counting
after an include_dir directive to be completely wrong.

Add missed failure check in AlterSystemSetConfigFile().  We don't really
expect ParseConfigFp() to fail, but that's not an excuse for not checking.

3 files changed, 17 insertions, 7 deletions

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 3515b6436ae..965a53cbfda 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201506281
+#define CATALOG_VERSION_NO	201506282
 
 #endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index d1cc8907d7c..3a40fa69c0a 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -3071,7 +3071,7 @@ DATA(insert OID = 2078 (  set_config		PGNSP PGUID 12 1 0 0 0 f f f f f f v 3 0 2
 DESCR("SET X as a function");
 DATA(insert OID = 2084 (  pg_show_all_settings	PGNSP PGUID 12 1 1000 0 0 f f f f t t s 0 0 2249 "" "{25,25,25,25,25,25,25,25,25,25,25,1009,25,25,25,23,16}" "{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}" "{name,setting,unit,category,short_desc,extra_desc,context,vartype,source,min_val,max_val,enumvals,boot_val,reset_val,sourcefile,sourceline,pending_restart}" _null_ _null_ show_all_settings _null_ _null_ _null_ ));
 DESCR("SHOW ALL as a function");
-DATA(insert OID = 3329 (  pg_show_all_file_settings PGNSP PGUID 12 1 1000 0 0 f f f f t t s 0 0 2249 "" "{25,23,23,25,25}" "{o,o,o,o,o}" "{sourcefile,sourceline,seqno,name,setting}" _null_ _null_ show_all_file_settings _null_ _null_ _null_ ));
+DATA(insert OID = 3329 (  pg_show_all_file_settings PGNSP PGUID 12 1 1000 0 0 f f f f t t v 0 0 2249 "" "{25,23,23,25,25,16,25}" "{o,o,o,o,o,o,o}" "{sourcefile,sourceline,seqno,name,setting,applied,error}" _null_ _null_ show_all_file_settings _null_ _null_ _null_ ));
 DESCR("show config file settings");
 DATA(insert OID = 1371 (  pg_lock_status   PGNSP PGUID 12 1 1000 0 0 f f f f t t v 0 0 2249 "" "{25,26,26,23,21,25,28,26,26,21,25,23,25,16,16}" "{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}" "{locktype,database,relation,page,tuple,virtualxid,transactionid,classid,objid,objsubid,virtualtransaction,pid,mode,granted,fastpath}" _null_ _null_ pg_lock_status _null_ _null_ _null_ ));
 DESCR("view system lock information");
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index ffe1168ccc1..49ec3840af3 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -121,26 +121,36 @@ typedef enum
 } GucSource;
 
 /*
- * Parsing the configuration file will return a list of name-value pairs
- * with source location info.
+ * Parsing the configuration file(s) will return a list of name-value pairs
+ * with source location info.  We also abuse this data structure to carry
+ * error reports about the config files.  An entry reporting an error will
+ * have errmsg != NULL, and might have NULLs for name, value, and/or filename.
+ *
+ * If "ignore" is true, don't attempt to apply the item (it might be an error
+ * report, or an item we determined to be duplicate).  "applied" is set true
+ * if we successfully applied, or could have applied, the setting.
  */
 typedef struct ConfigVariable
 {
 	char	   *name;
 	char	   *value;
+	char	   *errmsg;
 	char	   *filename;
 	int			sourceline;
+	bool		ignore;
+	bool		applied;
 	struct ConfigVariable *next;
 } ConfigVariable;
 
-extern bool ParseConfigFile(const char *config_file, const char *calling_file,
-				bool strict, int depth, int elevel,
+extern bool ParseConfigFile(const char *config_file, bool strict,
+				const char *calling_file, int calling_lineno,
+				int depth, int elevel,
 				ConfigVariable **head_p, ConfigVariable **tail_p);
 extern bool ParseConfigFp(FILE *fp, const char *config_file,
 			  int depth, int elevel,
 			  ConfigVariable **head_p, ConfigVariable **tail_p);
 extern bool ParseConfigDirectory(const char *includedir,
-					 const char *calling_file,
+					 const char *calling_file, int calling_lineno,
 					 int depth, int elevel,
 					 ConfigVariable **head_p,
 					 ConfigVariable **tail_p);