1 files changed, 118 insertions, 0 deletions
diff --git a/src/vdbetrace.c b/src/vdbetrace.c
index de123b5..c71a7c4 100644
--- a/src/vdbetrace.c
+++ b/src/vdbetrace.c
@@ -12,6 +12,8 @@
 **
 ** This file contains code used to insert the values of host parameters
 ** (aka "wildcards") into the SQL text output by sqlite3_trace().
+**
+** The Vdbe parse-tree explainer is also found here.
 */
 #include "sqliteInt.h"
 #include "vdbeInt.h"
@@ -152,3 +154,119 @@ char *sqlite3VdbeExpandSql(
 }
 
 #endif /* #ifndef SQLITE_OMIT_TRACE */
+
+/*****************************************************************************
+** The following code implements the data-structure explaining logic
+** for the Vdbe.
+*/
+
+#if defined(SQLITE_ENABLE_TREE_EXPLAIN)
+
+/*
+** Allocate a new Explain object
+*/
+void sqlite3ExplainBegin(Vdbe *pVdbe){
+  if( pVdbe ){
+    Explain *p;
+    sqlite3BeginBenignMalloc();
+    p = sqlite3_malloc( sizeof(Explain) );
+    if( p ){
+      memset(p, 0, sizeof(*p));
+      p->pVdbe = pVdbe;
+      sqlite3_free(pVdbe->pExplain);
+      pVdbe->pExplain = p;
+      sqlite3StrAccumInit(&p->str, p->zBase, sizeof(p->zBase),
+                          SQLITE_MAX_LENGTH);
+      p->str.useMalloc = 2;
+    }else{
+      sqlite3EndBenignMalloc();
+    }
+  }
+}
+
+/*
+** Return true if the Explain ends with a new-line.
+*/
+static int endsWithNL(Explain *p){
+  return p && p->str.zText && p->str.nChar
+           && p->str.zText[p->str.nChar-1]=='\n';
+}
+    
+/*
+** Append text to the indentation
+*/
+void sqlite3ExplainPrintf(Vdbe *pVdbe, const char *zFormat, ...){
+  Explain *p;
+  if( pVdbe && (p = pVdbe->pExplain)!=0 ){
+    va_list ap;
+    if( p->nIndent && endsWithNL(p) ){
+      int n = p->nIndent;
+      if( n>ArraySize(p->aIndent) ) n = ArraySize(p->aIndent);
+      sqlite3AppendSpace(&p->str, p->aIndent[n-1]);
+    }   
+    va_start(ap, zFormat);
+    sqlite3VXPrintf(&p->str, 1, zFormat, ap);
+    va_end(ap);
+  }
+}
+
+/*
+** Append a '\n' if there is not already one.
+*/
+void sqlite3ExplainNL(Vdbe *pVdbe){
+  Explain *p;
+  if( pVdbe && (p = pVdbe->pExplain)!=0 && !endsWithNL(p) ){
+    sqlite3StrAccumAppend(&p->str, "\n", 1);
+  }
+}
+
+/*
+** Push a new indentation level.  Subsequent lines will be indented
+** so that they begin at the current cursor position.
+*/
+void sqlite3ExplainPush(Vdbe *pVdbe){
+  Explain *p;
+  if( pVdbe && (p = pVdbe->pExplain)!=0 ){
+    if( p->str.zText && p->nIndent<ArraySize(p->aIndent) ){
+      const char *z = p->str.zText;
+      int i = p->str.nChar-1;
+      int x;
+      while( i>=0 && z[i]!='\n' ){ i--; }
+      x = (p->str.nChar - 1) - i;
+      if( p->nIndent && x<p->aIndent[p->nIndent-1] ){
+        x = p->aIndent[p->nIndent-1];
+      }
+      p->aIndent[p->nIndent] = x;
+    }
+    p->nIndent++;
+  }
+}
+
+/*
+** Pop the indentation stack by one level.
+*/
+void sqlite3ExplainPop(Vdbe *p){
+  if( p && p->pExplain ) p->pExplain->nIndent--;
+}
+
+/*
+** Free the indentation structure
+*/
+void sqlite3ExplainFinish(Vdbe *pVdbe){
+  if( pVdbe && pVdbe->pExplain ){
+    sqlite3_free(pVdbe->zExplain);
+    sqlite3ExplainNL(pVdbe);
+    pVdbe->zExplain = sqlite3StrAccumFinish(&pVdbe->pExplain->str);
+    sqlite3_free(pVdbe->pExplain);
+    pVdbe->pExplain = 0;
+    sqlite3EndBenignMalloc();
+  }
+}
+
+/*
+** Return the explanation of a virtual machine.
+*/
+const char *sqlite3VdbeExplanation(Vdbe *pVdbe){
+  return (pVdbe && pVdbe->zExplain) ? pVdbe->zExplain : 0;
+}
+#endif /* defined(SQLITE_DEBUG) */