Do not treat balance assignments with 0 diff as a null posting

Ledger is treating balance assignments that have a 0 diff as having
a null posting, leading to the posting being auto-balanced and
therefore causing incorrect values to be returned for the transaction.

I fixed this by just making the posting equal to amt - amt (0 in the
right commodity).

Fixes #1942

5 files changed, 117 insertions, 1 deletions

diff --git a/src/textual.cc b/src/textual.cc
index b4e51fbe..70bf4129 100644
--- a/src/textual.cc
+++ b/src/textual.cc
@@ -1705,7 +1705,11 @@ post_t * instance_t::parse_post(char *          line,
           // as amount cannot store more than 1 commodity.
           post->amount = diff.to_amount();
           DEBUG("textual.parse", "line " << context.linenum << ": "
-                << "Overwrite null posting");
+                << "Overwrite null posting with " << diff.to_amount());
+        } else {
+          post->amount = amt - amt;  // this is '0' with the correct commodity.
+          DEBUG("textual.parse", "line " << context.linenum << ": "
+                << "Overwrite null posting with zero diff with " << amt - amt);
         }
       } else {
         // balance assertion
diff --git a/test/regress/1942_a.test b/test/regress/1942_a.test
new file mode 100644
index 00000000..4d57f2ba
--- /dev/null
+++ b/test/regress/1942_a.test
@@ -0,0 +1,28 @@
+2018/01/01 * Opening Balance
+    Assets:Checking                             $1000.00
+    Equity:Opening Balances                    -$1000.00
+
+2018/01/01 * Budget
+    [Assets:Budget:Rent]                         $100.00
+    [Assets:Budget:Emergency]                    $200.00
+    [Assets:Checking]                           -$300.00
+
+2018/01/01 * Budget
+    [Assets:Budget:Rent]                       = $100.00
+    [Assets:Budget:Emergency]                  = $400.00
+    [Assets:Bank]                               -$500.00
+
+test bal Assets -> 1
+__ERROR__
+While parsing file "$FILE", line 13:
+While balancing transaction from "$FILE", lines 10-13:
+> 2018/01/01 * Budget
+>     [Assets:Budget:Rent]                       = $100.00
+>     [Assets:Budget:Emergency]                  = $400.00
+>     [Assets:Bank]                               -$500.00
+Unbalanced remainder is:
+            $-300.00
+Amount to balance against:
+             $200.00
+Error: Transaction does not balance
+end test
diff --git a/test/regress/1942_b.test b/test/regress/1942_b.test
new file mode 100644
index 00000000..03dd71a3
--- /dev/null
+++ b/test/regress/1942_b.test
@@ -0,0 +1,28 @@
+2018/01/01 * Opening Balance
+    Assets:Checking                             $1000.00
+    Equity:Opening Balances                    -$1000.00
+
+2018/01/01 * Budget
+    [Assets:Budget:Rent]                         $100.00
+    [Assets:Budget:Emergency]                    $200.00
+    [Assets:Checking]                           -$300.00
+
+2018/01/01 * Budget
+    [Assets:Budget:Rent]                    $0 = $100.00
+    [Assets:Budget:Emergency]                  = $400.00
+    [Assets:Bank]                               -$500.00
+
+test bal Assets -> 1
+__ERROR__
+While parsing file "$FILE", line 13:
+While balancing transaction from "$FILE", lines 10-13:
+> 2018/01/01 * Budget
+>     [Assets:Budget:Rent]                    $0 = $100.00
+>     [Assets:Budget:Emergency]                  = $400.00
+>     [Assets:Bank]                               -$500.00
+Unbalanced remainder is:
+            $-300.00
+Amount to balance against:
+             $200.00
+Error: Transaction does not balance
+end test
diff --git a/test/regress/1942_c.test b/test/regress/1942_c.test
new file mode 100644
index 00000000..a36099bd
--- /dev/null
+++ b/test/regress/1942_c.test
@@ -0,0 +1,28 @@
+2018/01/01 * Opening Balance
+    Assets:Checking                             $1000.00
+    Equity:Opening Balances                    -$1000.00
+
+2018/01/01 * Budget
+    Assets:Budget:Rent                           $100.00
+    Assets:Budget:Emergency                      $200.00
+    Assets:Checking                             -$300.00
+
+2018/01/01 * Budget
+    Assets:Budget:Rent                         = $100.00
+    Assets:Budget:Emergency                    = $400.00
+    Assets:Bank                                 -$500.00
+
+test bal Assets -> 1
+__ERROR__
+While parsing file "$FILE", line 13:
+While balancing transaction from "$FILE", lines 10-13:
+> 2018/01/01 * Budget
+>     Assets:Budget:Rent                         = $100.00
+>     Assets:Budget:Emergency                    = $400.00
+>     Assets:Bank                                 -$500.00
+Unbalanced remainder is:
+            $-300.00
+Amount to balance against:
+             $200.00
+Error: Transaction does not balance
+end test
diff --git a/test/regress/1942_d.test b/test/regress/1942_d.test
new file mode 100644
index 00000000..11b40494
--- /dev/null
+++ b/test/regress/1942_d.test
@@ -0,0 +1,28 @@
+2018/01/01 * Opening Balance
+    Assets:Checking                             $1000.00
+    Equity:Opening Balances                    -$1000.00
+
+2018/01/01 * Budget
+    Assets:Budget:Rent                           $100.00
+    Assets:Budget:Emergency                      $200.00
+    Assets:Checking                             -$300.00
+
+2018/01/01 * Budget
+    Assets:Budget:Rent                                 $0
+    Assets:Budget:Emergency                     = $400.00
+    Assets:Bank                                  -$500.00
+
+test bal Assets -> 1
+__ERROR__
+While parsing file "$FILE", line 13:
+While balancing transaction from "$FILE", lines 10-13:
+> 2018/01/01 * Budget
+>     Assets:Budget:Rent                                 $0
+>     Assets:Budget:Emergency                     = $400.00
+>     Assets:Bank                                  -$500.00
+Unbalanced remainder is:
+            $-300.00
+Amount to balance against:
+             $200.00
+Error: Transaction does not balance
+end test