[First Draft] postgre: add more error information to an error message (position, line number, partial SQL)

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/lib/pq v1.9.0
 	github.com/mattn/go-sqlite3 v1.14.6
 	github.com/pierrec/lz4 v2.6.0+incompatible // indirect
+	github.com/pkg/errors v0.9.1
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/stretchr/testify v1.7.0
 	github.com/urfave/cli/v2 v2.3.0

go.sum

@@ -35,6 +35,8 @@ github.com/mattn/go-sqlite3 v1.14.6/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
 github.com/pierrec/lz4 v2.6.0+incompatible h1:Ix9yFKn1nSPBLFl/yZknTp8TU5G4Ps0JDmguYK6iH1A=
 github.com/pierrec/lz4 v2.6.0+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/russross/blackfriday/v2 v2.0.1/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=

pkg/dbmate/db.go

@@ -2,7 +2,6 @@ package dbmate
 
 import (
 	"database/sql"
-	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -11,9 +10,13 @@ import (
 	"path/filepath"
 	"regexp"
 	"sort"
+	"strconv"
 	"time"
 
 	"github.com/amacneil/dbmate/pkg/dbutil"
+
+	"github.com/lib/pq"
+	"github.com/pkg/errors"
 )
 
 // DefaultMigrationsDir specifies default directory to find migration files
@@ -360,6 +363,38 @@ func (db *DB) migrate(drv Driver) error {
 			// run actual migration
 			result, err := tx.Exec(up.Contents)
 			if err != nil {
+				if pqErr, ok := err.(*pq.Error); ok {
+					pos, posErr := strconv.Atoi(pqErr.Position)
+					if posErr != nil {
+						// if unable to parse position as number
+						// pq must be giving us a bad number string or number
+						// is too big to fit in an int
+						return errors.Wrapf(err, "pos: %v", pqErr.Position)
+					}
+					// compute line number manually as pq driver does not provide it
+					column := 0
+					lineCount := 0
+					itColumn := 0
+					for _, c := range up.Contents[:pos] {
+						itColumn++
+						if c == '\n' {
+							column = itColumn
+							itColumn = 0
+							lineCount++
+						}
+					}
+					const fuzzyRange = 50
+					minPos := pos - fuzzyRange
+					if minPos < 0 {
+						minPos = 0
+					}
+					maxPos := pos + fuzzyRange
+					if maxPos >= len(up.Contents) {
+						maxPos = len(up.Contents) - 1
+					}
+					areaOfFailure := up.Contents[minPos:maxPos]
+					return errors.Wrapf(err, "position: %v, line: %v, column: %v, sql: %s\n", pqErr.Position, lineCount, column, areaOfFailure)
+				}
 				return err
 			} else if db.Verbose {
 				db.printVerbose(result)